Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “evolution of cell shape”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 757 records · Page 42Linked to original sources
PubMed2002

The Scaphopoda.

The Scaphopoda are marine infaunal carnivores that feed on foraminiferans and other microorganisms selected and manipulated by their unique feeding tentacles or captacula. Their tusk-like shell is open at both ends; the burrowing foot and captacula protrude anteriorly, while respiratory currents pass through the posterior opening. Although the scaphopods comprise one of the smallest molluskan classes in terms of species diversity, they have a worldwide distribution ranging from intertidal to depths in excess of 6000 m. Despite detailed monographic work from the late nineteenth and early twentieth centuries, however, the biology of scaphopods is today among the least understood of mollusks. To some extent, this is related to a significant departure from more typical molluscan organization inferred from studies of the larger classes. For example, the mantle cavity is elongate and restricted in space, and several associated organs are lost, including the osphradium and ctenidia; the latter is associated with the loss of auricles from the scaphopod heart. There is also little record of ontogeny in the adult shell, as the older portion is periodically decollated to maintain the posterior aperture for passage of inhalant and exhalant currents. This and other constraints on scaphopod diversification are reflected in the range limits of shell shape within the class. In contrast, the "Dentalium" egg has been a model system for experimental embryology, particularly in studies of cell lineage and early morphogenesis. Later larval development and most organogenesis is nonetheless poorly known, although recent studies have considerably enhanced our knowledge in this area. Global biogeographic patterns of scaphopod diversity have been studied only preliminarily. A general decrease in diversity with depth is broken by small diversity peaks at bathyal depths. There is also evidence for a marked latitudinal diversity gradient in the world's oceans, near equatorial in the Pacific but at approximately 20 degrees N in the Atlantic. Scaphopods have a wide diversity of ecto- and endo-symbiotic associations with other organisms, including commensal bacteria and ciliates, mutualistic anemones and corals, and parasitic algae and platyhelminths. Other documented associations include predation by naticid gastropods and ratfish, and the inhabitation of empty scaphopod shells by a variety of sipunculans and hermit crabs. Phylogeny within the class is still unresolved, although significant progress has been made recently in documenting morphological variation among families, genera, and species for application in a cladistic context. The evolutionary relationships of Scaphopoda within Mollusca are farther from resolution, with every conchiferan class a proposed sister group among modern analyses. Molecular avenues should provide significant progress in scaphopod phylogenetics, as indicated by recent comparative sequence analysis and gene expression patterns. Scaphopods comprise the most recent class of mollusks to appear in the fossil record, dating at least from the Mississippian Carboniferous (362.5 My). They appear from first-order occurrence data to have a substantially documented fossil record, with several sharp extinction and radiation events evident during their comparatively short geologic history. The unresolved position of the Scaphopoda within molluscan phylogeny, and their relatively limited range of morphological disparity but substantial derivation from other conchiferans, renders the scaphopods an enigmatic group. They represent a significant evolutionary avenue within the Mollusca, but one that is poorly examined. Nonetheless, comprehensive phylogenetic analysis and documentation of diversity within this small, monophyletic, class-level taxon, well-preserved in the fossil record, is imminently tractable, and presents a singular opportunity in the study of molluscan evolution.

Animals↗
PubMed2026

Diversification of Cellulose Synthase (CESA) Genes in Mosses Suggests Both Ancient and Recent Gene duplications.

Cellulose is an important polysaccharide that constitutes all plant cell walls, giving them strength and stability. The plant cellulose synthase (CESA) gene family, which encodes the catalytic subunits of cellulose synthesis complexes (CSCs), has diversified independently in several plant lineages, providing an interesting model for understanding selection for gene duplication. Here we quantified the presence of CESA genes across mosses to understand how the process of gene family diversification occurred in this group and how it parallels diversification in other groups. We first examined the CESA gene family in eight species of mosses across seven families for which whole genome assemblies were available. We then identified CESA genes from additional species, for which only short-read sequence data was available, by using BLAST searches and targeted gene assemblies. We validated this approach by comparing the assembled paralogs from the short-read data to the genes identified from whole genome assemblies in the eight reference species. This approach allowed us to identify paralogs directly from short-read data and greatly expand our sample set. Results from the combined empirical data support the hypothesis that CESA genes diversified within the moss lineage at least as early as the mesozoic period, during or possibly even prior to the onset of moss diversification, but also continue to diversify within modern species. In addition, we found evidence for purifying selection as the dominant force shaping these genes and observed that different lineages experienced different levels of evolutionary constraint. Lastly, our approach to assemble paralogs has the potential to allow researchers to improve analyses of gene duplication events.

Physcomitrium patens↗
PubMed2006

Shaping leg muscles in Drosophila: role of ladybird, a conserved regulator of appendicular myogenesis.

Legs are locomotor appendages used by a variety of evolutionarily distant vertebrates and invertebrates. The primary biological leg function, locomotion, requires the formation of a specialised appendicular musculature. Here we report evidence that ladybird, an orthologue of the Lbx1 gene recognised as a hallmark of appendicular myogenesis in vertebrates, is expressed in leg myoblasts, and regulates the shape, ultrastructure and functional properties of leg muscles in Drosophila. Ladybird expression is progressively activated in myoblasts associated with the imaginal leg disc and precedes that of the founder cell marker dumbfounded. The RNAi-mediated attenuation of ladybird expression alters properties of developing myotubes, impairing their ability to grow and interact with the internal tendons and epithelial attachment sites. It also affects sarcomeric ultrastructure, resulting in reduced leg muscle performance and impaired mobility in surviving flies. The over-expression of ladybird also results in an abnormal pattern of dorsally located leg muscles, indicating different requirements for ladybird in dorsal versus ventral muscles. This differential effect is consistent with the higher level of Ladybird in ventrally located myoblasts and with positive ladybird regulation by extrinsic Wingless signalling from the ventral epithelium. In addition, ladybird expression correlates with that of FGF receptor Heartless and the read-out of FGF signalling downstream of FGF. FGF signals regulate the number of leg disc associated myoblasts and are able to accelerate myogenic differentiation by activating ladybird, leading to ectopic muscle fibre formation. A key role for ladybird in leg myogenesis is further supported by its capacity to repress vestigial and to down-regulate the vestigial-governed flight muscle developmental programme. Thus in Drosophila like in vertebrates, appendicular muscles develop from a specialised pool of myoblasts expressing ladybird/Lbx1. The ladybird/Lbx1 gene family appears as a part of an ancient genetic circuitry determining leg-specific properties of myoblasts and making an appendage adapted for locomotion.

Animals↗
PubMed2006

Crystal structure of an archaeal actin homolog.

Prokaryotic homologs of the eukaryotic structural protein actin, such as MreB and ParM, have been implicated in determination of bacterial cell shape, and in the segregation of genomic and plasmid DNA. In contrast to these bacterial actin homologs, little is known about the archaeal counterparts. As a first step, we expressed a predicted actin homolog of the thermophilic archaeon Thermoplasma acidophilum, Ta0583, and determined its crystal structure at 2.1A resolution. Ta0583 is expressed as a soluble protein in T.acidophilum and is an active ATPase at physiological temperature. In vitro, Ta0583 forms sheets with spacings resembling the crystal lattice, indicating an inherent propensity to form filamentous structures. The fold of Ta0583 contains the core structure of actin and clearly belongs to the actin/Hsp70 superfamily of ATPases. Ta0583 is approximately equidistant from actin and MreB on the structural level, and combines features from both eubacterial actin homologs, MreB and ParM. The structure of Ta0583 co-crystallized with ADP indicates that the nucleotide binds at the interface between the subdomains of Ta0583 in a manner similar to that of actin. However, the conformation of the nucleotide observed in complex with Ta0583 clearly differs from that in complex with actin, but closely resembles the conformation of ParM-bound nucleotide. On the basis of sequence and structural homology, we suggest that Ta0583 derives from a ParM-like actin homolog that was once encoded by a plasmid and was transferred into a common ancestor of Thermoplasma and Ferroplasma. Intriguingly, both genera are characterized by the lack of a cell wall, and therefore Ta0583 could have a function in cellular organization.

Actins↗
PubMed2004

Continued colonization of the human genome by mitochondrial DNA.

Integration of mitochondrial DNA fragments into nuclear chromosomes (giving rise to nuclear DNA sequences of mitochondrial origin, or NUMTs) is an ongoing process that shapes nuclear genomes. In yeast this process depends on double-strand-break repair. Since NUMTs lack amplification and specific integration mechanisms, they represent the prototype of exogenous insertions in the nucleus. From sequence analysis of the genome of Homo sapiens, followed by sampling humans from different ethnic backgrounds, and chimpanzees, we have identified 27 NUMTs that are specific to humans and must have colonized human chromosomes in the last 4-6 million years. Thus, we measured the fixation rate of NUMTs in the human genome. Six such NUMTs show insertion polymorphism and provide a useful set of DNA markers for human population genetics. We also found that during recent human evolution, Chromosomes 18 and Y have been more susceptible to colonization by NUMTs. Surprisingly, 23 out of 27 human-specific NUMTs are inserted in known or predicted genes, mainly in introns. Some individuals carry a NUMT insertion in a tumor-suppressor gene and in a putative angiogenesis inhibitor. Therefore in humans, but not in yeast, NUMT integrations preferentially target coding or regulatory sequences. This is indeed the case for novel insertions associated with human diseases and those driven by environmental insults. We thus propose a mutagenic phenomenon that may be responsible for a variety of genetic diseases in humans and suggest that genetic or environmental factors that increase the frequency of chromosome breaks provide the impetus for the continued colonization of the human genome by mitochondrial DNA.

Algorithms↗
PubMed2002

The genomic sequence of the murine major vault protein and its promoter.

Vaults are ribonucleoproteins of unknown function, consisting of three different proteins and multiple copies of small untranslated RNA molecules. One of the protein subunits has been identified as TEP1, a protein that is also associated with the telomerase complex. Another protein appears to contain a functional PARP domain and is hence called VPARP. The third protein, major vault protein (MVP), is believed to make up 70% of the total mass of the vault complex and to be responsible for the typical barrel-shaped structure of vaults. We have isolated the murine MVP cDNA and compared the amino acid sequence with MVP from other species. Over 90% of sequence identity was found between mouse, human and rat, and a considerable degree of identity between mouse and MVPs from lower eukaryotes. We also found that the genomic structure of the murine MVP gene closely resembles the organization of the human MVP gene, both consisting of 15 exons of which most have exactly the same size. Finally we have isolated a genomic region upstream (and partially overlapping) the first untranslated exon, that displayed promoter activity in a luciferase reporter assay. Furthermore, we showed that the sequences from the first exon together with the 5'-end of the first intron enhance the promoter activity, implying the presence of essential promoter elements in this region. Alignment of the murine promoter region with the homologous sequences of the human gene revealed an identity of 58%. The apparent presence of conserved promoter elements suggests a similar regulation of human and murine MVP expression.

Animals↗
PubMed1998

Assembly and architecture of invertebrate cytoplasmic intermediate filaments reconcile features of vertebrate cytoplasmic and nuclear lamin-type intermediate filaments.

The two major intermediate filament (IF) proteins from the esophagus epithelium of the snail Helix pomatia and the two major IF proteins from muscle tissue of the nematode Ascaris suum were investigated under a variety of assembly conditions. The lowest-order complexes from each of the four protostomic invertebrate (p-INV) IF proteins are parallel, unstaggered dimers involving two-stranded alpha-helical coiled coil formation of their approximately 350 amino acid residue central rod domain (i.e. long-rod). In the electron microscope these are readily recognized by their distinct approximately 56 nm long rod with two globular domains (i.e. representing the non-helical carboxy-terminal tail domain of the p-INV IF proteins) attached at one end, closely resembling vertebrate lamin dimers. The next-higher-order oligomers are tetramers, which are easily recognized by their two pairs of globular tail domains attached at either end of a approximately 72 nm long central rod portion. According to their size and shape, these tetramers are built from two dimers associated laterally in an antiparallel, approximately half-staggered fashion via the amino-terminal halves of their rod domains. This is similar to the NN-type tetramers found as the most abundant oligomer species in all types of vertebrate cytoplasmic IF proteins, which contain a approximately 310 amino acid residue central rod domain (i.e. short-rod). As a first step toward filament formation, the p-INV IF tetramers anneal longitudinally into protofilaments by antiparallel CC-type association of the carboxy-terminal halves of their dimer rods. The next step involves radial growth, occurring initially through lateral association of two four-chain protofilaments into octameric subfibrils, which then further associate into mature, full-width filaments. Head-to-tail polymers of dimers and paracrystalline fibers commonly observed with vertebrate lamins were only rarely seen with p-INV IF proteins. The globular domains residing at the carboxy-terminal end of p-INV IF dimers were studding the surface of the filaments at regular, approximately 24.5 nm intervals, thereby giving them a "beaded" appearance with an axial periodicity of about 24.5 nm, which is approximately 3 nm longer than the corresponding approximately 21.5 nm repeat pattern exhibited by short-rod vertebrate IFs.

Animals↗
PubMed2005

Identification and characterization of human archaemetzincin-1 and -2, two novel members of a family of metalloproteases widely distributed in Archaea.

Systematic analysis of degradomes, the complete protease repertoires of organisms, has demonstrated the large and growing complexity of proteolytic systems operating in all cells and tissues. We report here the identification of two new human metalloproteases that have been called archaemetzincin-1 (AMZ1) and archaemetzincin-2 (AMZ2) to emphasize their close relationship to putative proteases predicted by bioinformatic analysis of archaeal genomes. Both human proteins contain a catalytic domain with a core motif (HEXXHXXGX3CX4CXMX17CXXC) that includes an archetypal zinc-binding site, the methionine residue characteristic of metzincins, and four conserved cysteine residues that are not present at the equivalent positions of other human metalloproteases. Analysis of genome sequence databases revealed that AMZs are widely distributed in Archaea and vertebrates and contribute to the defining of a new metalloprotease family that has been called archaemetzincin. However, AMZ-like sequences are absent in a number of model organisms from bacteria to nematodes. Phylogenetic analysis showed that these enzymes have undergone a complex evolutionary process involving a series of lateral gene transfer, gene loss, and genetic duplication events that have shaped this novel family of metalloproteases. Northern blot analysis showed that AMZ1 and AMZ2 exhibit distinct expression patterns in human tissues. AMZ1 is mainly detected in liver and heart whereas AMZ2 is predominantly expressed in testis and heart, although both are also detectable at lower levels in other tissues. Both human enzymes were produced in Escherichia coli, and the purified recombinant proteins hydrolyzed synthetic substrates and bioactive peptides, demonstrating that they are functional proteases. Finally, these activities were abolished by inhibitors of metalloproteases, providing further evidence that AMZs belong to this catalytic class of proteolytic enzymes.

Amino Acid Motifs↗
PubMed1996

The fission yeast sts5+ gene is required for maintenance of growth polarity and functionally interacts with protein kinase C and an osmosensing MAP-kinase pathway.

Cell morphogenesis is a fundamental phenomenon that involves understanding a number of biological processes including the developmental program, polarity and cell division. Fission yeast sts5 mutant cells are round rather than cylindrical with cortical actin randomly dispersed. Genetic analyses demonstrate that the sts5+ gene is required for maintenance of cell shape during interphase when the cell normally exhibits polarised growth. The sts5 mutant is not defective in cell wall integrity. Deletion of ppe1+, which encodes a type 2A-like protein phosphatase, shows similar phenotypes to the sts5 mutant and these two mutations are synthetically lethal. Multicopy plasmids containing either the protein kinase C-like gene pck1+ or the protein tyrosine phosphatase pyp1+, an inhibitor of an osmosensing Sty1/Spc1 MAP-kinase, are capable of suppressing the sts5 mutation. Consistent with this, we have found that the wis1 mutation, which is defective in a MAP-kinase kinase of the pathway, suppresses the sts5 mutation. The predicted sts5+ gene product exhibits sequence similarity to two yeast proteins, Dis3 and Ssd1 and a nematode protein, F46E8.6, where the former two yeast proteins have been shown to be involved in cell cycle control and cell morphogenesis. The sts5+ gene is not essential for cell viability, but is absolutely required for polarised growth as the gene disruption showed the same phenotypes as those of the original mutants. Overexpression of the sts5+ gene resulted in altered cell morphology and, cortical actin in these overproducing cells was also abnormal, fainter and often dispersed. Anti-Sts5 antibody specifically detected a 130 kDa protein by western blotting. A green fluorescent protein-Sts5 fusion protein localised in the cytoplasm with a discrete punctate pattern, suggesting that the Sts5 protein is a component of a novel structure. These results have indicated that the Sts5 protein is a crucial determinant of polarised growth and that it functionally interacts with the serine/threonine phosphatase, protein kinase C, and an osmosensing MAP-kinase to maintain cell morphology.

Amino Acid Sequence↗
PubMedDate not supplied

[The organization of germinal material and dynamics of mother sporocyst reproduction in the genus Echinostoma (Trematoda: Echinostomatidae)].

The reproduction in the first parthenogenetic generation--mother sporocyst (MS) in two species of echinostomes (E. caproni, E. paraensei) is investigated. A group of densely packed cells, which noticeably differ from others, occupies the posterior part of the miracidium. They are characterized by large sizes and a large bubble-shaped nucleus with heterogeneous nucleolus and strong dispersed chromatin. The use of histological and electron microscopic methods has shown that with observed similarity these cells are classified in two tyoes and have a completely different origin. First of all, large secretory cells stand out. In E. caproni miracidia their number averages 6.8 +/- 0.2 and linear sizes is 10-12 microns. Secretory cells possess a large bubble-shaped nucleus. The caryoplasm looks optically empty because of strong dispersion of chromatin. A large nucleolus occupies a bit eccentric position. Eosinophilic cytoplasm contains poorly noticeable at light-optical level accumulation of small granules. The second group of cells is represented by typical germinal cells (GC). The number of GC does not exceed six. Their polymorphy is well above that of secretory cells. The sizes of GC vary from 5.4 to 9 microns. The largest cells (8.1-9 microns) occupy the front position and usually are located between secretory cells. Intensively basophilic cytoplasm surrounds bubble-shaped nucleus with a large nucleolus like border with uniforming thickness. The heterochromatin is evenly distributed over the caryoplasm. Its content of nuclei is more than that in nuclei of secretory cells. That is why they do not look optically empty. So, it is "mature" germinal cells. Four or five cells are located directly behind "mature" cells. Their sizes are gradually decrease towards the posterior of the miracidium (the diameter of the smallest cells reaches 5.4 microns). Nuclei with a centrally located nucleolus are characterized by larger amount and more condensation of the heterochromatin than those in "mature" cells. Meanwhile, they concern to nuclei of bubble-shaped type. In general, all cells of second type represent the primary germinal cells distinguished by the stage of their differentiation. Also, 2-3 undifferentiated cells occupy the most posterior part of the miracidium. Their sizes average 5.55 +/- 0.18 microns. The nucleus contains a lot of densely packed heterochromatin. On parasitic phase of MS development undifferentiated cells give rise to secondary GC. Electron microscopic data in details confirm the situation described above. The essentially similar results were received during the investigation of E. Paraensei miracidia. The differences are observed in parameterical characteristics of germinal material and in small variability of the extent of germinal material development. With E. paraensei, germinal material may be represented by not only GC and undifferentiated cells, but one germ as well. So, our investigation has shown that germinal material of echinostomes represents typical germinal mass. The germinal material condition does not change on parasitic phase of E. caproni MS development during the first day of post infection (PI). The activization of germinal material coincides in the time with the beginning of schizocoel formation in 2 Days PI. On the 3rd day of PI, the proliferation of undifferentiated cells begins and the first germs are free to float in enormous schizocoel. After 8 days of PI, MS release the first rediae. During the following 2-3 days the other rediae formed by primary GC left MS. The release of rediae derived from secondary GC was observed later. So, E. caproni MS give rise to 12-16 rediae which is much less than the number of GC formed in MS. The earlier release of the first E. paraensei rediae by MS is predetermined by the difference in the structure of germinal mass in E. paraensei miracidia. Therefore, Echinostomatidae is intermediate between two groups of trematodes. The first group has MS that completely realize reproductive function in the time of miracidial formation; but the second group includes higher trematodes characterized by the transfer of reproductive time on a parasitic phase of MS development. The question concerning to so-called "pedogenetic larvae of trematodes" is discussed.

Animals↗
PubMed2006

Combining expression and comparative evolutionary analysis. The COBRA gene family.

Plant cell shape is achieved through a combination of oriented cell division and cell expansion and is defined by the cell wall. One of the genes identified to influence cell expansion in the Arabidopsis (Arabidopsis thaliana) root is the COBRA (COB) gene that belongs to a multigene family. Three members of the AtCOB gene family have been shown to play a role in specific types of cell expansion or cell wall biosynthesis. Functional orthologs of one of these genes have been identified in maize (Zea mays) and rice (Oryza sativa; Schindelman et al., 2001; Li et al., 2003; Brown et al., 2005; Persson et al., 2005; Ching et al., 2006; Jones et al., 2006). We present the maize counterpart of the COB gene family and the COB gene superfamily phylogeny. Most of the genes belong to a family with two main clades as previously identified by analysis of the Arabidopsis family alone. Within these clades, however, clear differences between monocot and eudicot family members exist, and these are analyzed in the context of Type I and Type II cell walls in eudicots and monocots. In addition to changes at the sequence level, gene regulation of this family in a eudicot, Arabidopsis, and a monocot, maize, is also characterized. Gene expression is analyzed in a multivariate approach, using data from a number of sources, including massively parallel signature sequencing libraries, transcriptional reporter fusions, and microarray data. This analysis has revealed that the expression of Arabidopsis and maize COB gene family members is highly developmentally and spatially regulated at the tissue and cell type-specific level, that gene superfamily members show overlapping and unique expression patterns, and that only a subset of gene superfamily members act in response to environmental stimuli. Regulation of expression of the Arabidopsis COB gene family members has highly diversified in comparison to that of the maize COB gene superfamily members. We also identify BRITTLE STALK 2-LIKE 3 as a putative ortholog of AtCOB.

Amino Acid Sequence↗
PubMed2004

Chronoastrobiology: proposal, nine conferences, heliogeomagnetics, transyears, near-weeks, near-decades, phylogenetic and ontogenetic memories.

"Chronoastrobiology: are we at the threshold of a new science? Is there a critical mass for scientific research?" A simple photograph of the planet earth from outer space was one of the greatest contributions of space exploration. It drove home in a glance that human survival depends upon the wobbly dynamics in a thin and fragile skin of water and gas that covers a small globe in a mostly cold and vast universe. This image raised the stakes in understanding our place in that universe, in finding out where we came from and in choosing a path for survival. Since that landmark photograph was taken, new astronomical and biomedical information and growing computer power have been revealing that organic life, including human life, is and has been connected to invisible (non-photic) forces, in that vast universe in some surprising ways. Every cell in our body is bathed in an external and internal environment of fluctuating magnetism. It is becoming clear that the fluctuations are primarily caused by an intimate and systematic interplay between forces within the bowels of the earth--which the great physician and father of magnetism William Gilbert called a 'small magnet'--and the thermonuclear turbulence within the sun, an enormously larger magnet than the earth, acting upon organisms, which are minuscule magnets. It follows and is also increasingly apparent that these external fluctuations in magnetic fields can affect virtually every circuit in the biological machinery to a lesser or greater degree, depending both on the particular biological system and on the particular properties of the magnetic fluctuations. The development of high technology instruments and computer power, already used to visualize the human heart and brain, is furthermore making it obvious that there is a statistically predictable time structure to the fluctuations in the sun's thermonuclear turbulence and thus to its magnetic interactions with the earth's own magnetic field and hence a time structure to the magnetic fields in organisms. Likewise in humans, and in at least those other species that have been studied, computer power has enabled us to discover statistically defined endogenous physiological rhythms and further direct effects that are associated with these invisible geo- and heliomagnetic cycles. Thus, what once might have been dismissed as noise in both magnetic and physiological data does in fact have structure. And we may be at the threshold of understanding the biological and medical meaning and consequences of these patterns and biological-astronomical linkages as well. Structures in time are called chronomes; their mapping in us and around us is called chronomics. The scientific study of chronomes is chronobiology. And the scientific study of all aspects of biology related to the cosmos has been called astrobiology. Hence we may dub the new study of time structures in biology with regard to influences from cosmo- helio- and geomagnetic rhythms chronoastrobiology. It has, of course, been understood for centuries that the movements of the earth in relation to the sun produce seasonal and daily cycles in light energy and that these have had profound effects on the evolution of life. It is now emerging that rhythmic events generated from within the sun itself, as a large turbulent magnet in its own right, can have direct effects upon life on earth. Moreover, comparative studies of diverse species indicate that there have also been ancient evolutionary effects shaping the endogenous chronomic physiological characteristics of life. Thus the rhythms of the sun can affect us not only directly, but also indirectly through the chronomic patterns that solar magnetic rhythms have created within our physiology in the remote past. For example, we can document the direct exogenous effects of given specific solar wind events upon human blood pressure and heart rate. We also have evidence of endogenous internal rhythms in blood pressure and heart rate that are close to but not identical to the period length of rhythms in the solar wind. These were installed genetically by natural selection at some time in the distant geological past. This interpretive model of the data makes the prediction that the internal and external influences on heart rate and blood pressure can reinforce or cancel each other out at different times. A study of extensive clinical and physiological data shows that the interpretive model is robust and that internal and external effects are indeed augmentative at a statistically significant level. Chronoastrobiological studies are contributing to basic science--that is, our understanding is being expanded as we recognize heretofore unelaborated linkages of life to the complex dynamics of the sun, and even to heretofore unelaborated evolutionary phenomena. Once, one might have thought of solar storms as mere transient 'perturbations' to biology, with no lasting importance. Now we are on the brink of understanding that solar turbulences have played a role in shaping endogenous physiological chronomes. There is even documentation for correlations between solar magnetic cycles and psychological swings, eras of belligerence and of certain expressions of sacred or religious feelings. Chronoastrobiology can surely contribute to practical applications as well as to basic science. It can help develop refinements in our ability to live safely in outer space, where for example at the distance of the moon the magnetic influences of the sun will have an effect upon humans unshielded by the earth's native magnetic field. We should be better able to understand these influences as physiological and mechanical challenges, and to improve our estimations of the effects of exposure. Chronoastrobiology moreover holds great promise in broadening our perspectives and powers in medicine and public health right here upon the surface of the earth. Even the potential relevance of chronoastrobiology for practical environmental and agricultural challenges cannot be ruled out at this early stage in our understanding of the apparently ubiquitous effects of magnetism and hence perhaps of solar magnetism on life. The evidence already mentioned that fluctuations in solar magnetism can influence gross clinical phenomena such as rates of strokes and heart attacks, and related cardiovascular variables such as blood pressure and heart rate, should illustrate the point that the door is open to broad studies of clinical implications. The medical value of better understanding magnetic fluctuations as sources of variability in human physiology falls into several categories: 1) The design of improved analytical and experimental controls in medical research. Epidemiological analyses require that the multiple sources causing variability in physiological functions and clinical phenomena be identified and understood as thoroughly as possible, in order to estimate systematic alterations of any one variable. 2) Preventive medicine and the individual patients'care. There are no flat 'baselines', only reference chronomes. Magnetic fluctuations can be shown statistically to exacerbate health problems in some cases. The next step should be to determine whether vulnerable individuals can be identified by individual monitoring. Such vulnerable patients may then discover that they have the option to avoid circumstances associated with anxiety during solar storms, and/or pay special attention to their medication or other treatments. Prehabilitation by self-help can hopefully complement and eventually replace much costly rehabilitation. 3) Basic understanding of human physiological mechanisms. The chronomic organization of physiology implies a much more subtle dynamic integration of functions than is generally appreciated. All three categories of medical value in turn pertain to the challenges for space science of exploring and colonizing the solar system. The earth's native magnetic field acts like an enormous umbrella that offers considerable protection on the surface from harsh solar winds of charged particles and magnetic fluxes. The umbrella becomes weaker with distance from the earth and will offer little protection for humans, other animals, and plants in colonies on the surface of the moon or beyond. Thus it is important before more distant colonization is planned or implemented to better understand those magnetism-related biological- solar interactions that now can be studied conveniently on earth. (ABSTRACT TRUNCATED)

Chronobiology Phenomena↗
PubMed2003

Temperature effects on the rheological properties of current polyether and polysiloxane impression materials during setting.

STATEMENT OF PROBLEM: Rheological tests of elastomeric impression materials during setting have been most often conducted at room temperature rather than at intraoral temperature. Because temperature may affect properties and the setting kinetics, clinically relevant inferences may not be accurate with studies conducted at room temperature. PURPOSE: The purpose of this study was to determine the viscoelastic properties of new low- and medium-viscosity elastomeric impression materials during setting at 33 degrees C and to evaluate the medium-viscosity materials at 3 additional temperatures. MATERIAL AND METHODS: The impression materials investigated at 33 degrees C were 2 polyvinylsiloxanes (PVS) (Aquasil Deca and Aquasil LV) and 5 polyethers (PE) (Impregum Penta, Impregum Penta Soft H, Impregum Penta Soft L, Impregum Garant Soft L, and Permadyne Garant L). Three impression materials (Aquasil Deca, Impregum Penta, and Impregum Penta Soft H) were also investigated at 25 degrees, 29 degrees, and 37 degrees C. Time-dependent oscillatory rheometry was carried out on these materials (n=3) with a rheometer with a 25-mm diameter parallel plate cell. The storage modulus (G') and the loss tangent (tandelta) were determined as functions of time over a period from 0 seconds to 900 seconds, commencing 40 seconds after mixing. Induction time (t(ind)) or initial setting time and tandelta, the relative liquidlike behavior, were also computed. A single-factor analysis of variance (ANOVA) was used for the properties determined at 33 degrees C and a 2-factor ANOVA was used for the temperature studies, with hypothesis testing at alpha=.05. RESULTS: The G'(t) curves for all materials displayed the expected sigmoidal shape with time, with the solid-like behavior rising slowly, then more rapidly, and again slowly to final set. The initial setting time (t(ind)) was found to be approximately 2.8 minutes for the PVS materials and for Impregum Penta and Impregum Penta Soft H, but was significantly longer for the remaining 3 PE low viscosity materials. The solid-like behavior (G') at final set or shear modulus differed among all materials, ranging from 1.0 MPa for Aquasil Decca, 1.69 for Impregum Penta Soft H, and 1.8 MPa for Impregum Penta. G' for low-viscosity materials ranged from 0.66 MPa for Aquasil LV and 0.79 MPa for Permadyne Garant L to 1.2 MPa for Impregum Penta Soft L. The loss tangent at 40 seconds tandelta (t(0)) varied among medium and low viscosity materials, ranging from liquid-like behavior of 4.3 for Permadyne Garant and less than unity or significant solid-like behavior for Impregum Penta. All materials showed tandelta values less than unity at their setting times. The temperature studies revealed significant changes in the kinetics of setting, with the setting time decreasing more than 3-fold between 25 degrees and 37 degrees C for the Aquasil Deca and the Impregum Penta Soft H and more than 2-fold for the Impregum Penta. At room temperature of 25 degrees C, the storage modulus for Impregum Penta Soft H and Aquasil Deca was 1.1% and 37.5% lower than Impregum Penta, respectively. CONCLUSION: The development of the viscoelastic rheological properties with time for 3 medium- and 4 low-viscosity impression materials at 33 degrees C showed significant differences in the setting time and the magnitude of the storage modulus. Compared with Impregum Penta, the new Impregum Penta Soft H was 6% less stiff when set, compared with 44% lower stiffness for the medium viscosity addition silicone. Temperature studies between 25 degrees C and 37 degrees C revealed strong temperature sensitivity of the kinetics of setting and evolution with time of their rheological properties.

Analysis of Variance↗
PubMed2001

Gonococcal MinD affects cell division in Neisseria gonorrhoeae and Escherichia coli and exhibits a novel self-interaction.

The Min proteins are involved in determining cell division sites in bacteria and have been studied extensively in rod-shaped bacteria. We have recently shown that the gram-negative coccus Neisseria gonorrhoeae contains a min operon, and the present study investigates the role of minD from this operon. A gonococcal minD insertional mutant, CJSD1, was constructed and exhibited both grossly abnormal cell division and morphology as well as altered cell viability. Western blot analysis verified the absence of MinD from N. gonorrhoeae (MinD(Ng)) in this mutant. Hence, MinD(Ng) is required for maintaining proper cell division and growth in N. gonorrhoeae. Immunoblotting of soluble and insoluble gonococcal cell fractions revealed that MinD(Ng) is both cytosolic and associated with the insoluble membrane fraction. The joint overexpression of MinC(Ng) and MinD(Ng) from a shuttle vector resulted in a significant enlargement of gonococcal cells, while cells transformed with plasmids encoding either MinC(Ng) or MinD(Ng) alone did not display noticeable morphological changes. These studies suggest that MinD(Ng) is involved in inhibiting gonococcal cell division, likely in conjunction with MinC(Ng). The alignment of MinD sequences from various bacteria showed that the proteins are highly conserved and share several regions of identity, including a conserved ATP-binding cassette. The overexpression of MinD(Ng) in wild-type Escherichia coli led to cell filamentation, while overexpression in an E. coli minD mutant restored a wild-type morphology to the majority of cells; therefore, gonococcal MinD is functional across species. Yeast two-hybrid studies and gel-filtration and sedimentation equilibrium analyses of purified His-tagged MinD(Ng) revealed a novel MinD(Ng) self-interaction. We have also shown by yeast two-hybrid analysis that MinD from E. coli interacts with itself and with MinD(Ng). These results indicate that MinD(Ng) is required for maintaining proper cell division and growth in N. gonorrhoeae and suggests that the self-interaction of MinD may be important for cell division site selection across species.

Adenosine Triphosphatases↗
PubMed2006

An experimental manipulation of life-history trajectories and resistance to oxidative stress.

Optimal investment into life-history traits depends on the environmental conditions that organisms are likely to experience during their life. Evolutionary theory tells us that optimal investment in reproduction versus maintenance is likely to shape the pattern of age-associated decline in performance, also known as aging. The currency that is traded against different vital functions is, however, still debated. Here, we took advantage of a phenotypic manipulation of individual quality in early life to explore (1) long-term consequences on life-history trajectories, and (2) the possible physiological mechanism underlying the life-history adjustments. We manipulated phenotypic quality of a cohort of captive zebra finches (Taeniopygia guttata) by assigning breeding pairs to either an enlarged or a reduced brood. Nestlings raised in enlarged broods were in poorer condition than nestlings raised in reduced broods. Interestingly, the effect of environmental conditions experienced during early life extended to the age at first reproduction. Birds from enlarged broods delayed reproduction. Birds that delayed reproduction produced less offspring but lived longer, although neither fecundity nor longevity were directly affected by the experimental brood size. Using the framework of the life-table response experiment modeling, we also explored the effect of early environmental condition on population growth rate and aging. Birds raised in reduced broods tended to have a higher population growth rate, and a steeper decrease of reproductive value with age than birds reared in enlarged broods. Metabolic resources necessary to fight off the damaging effect of reactive oxygen species (ROS) could be the mechanism underlying the observed results, as (1) birds that engaged in a higher number of breeding events had a weaker red blood cell resistance to oxidative stress, (2) red blood cell resistance to oxidative stress predicted short-term mortality (but not longevity), and (3) was related with a parabolic function to age. Overall, these results highlight that early condition can have long-term effects on life-history trajectories by affecting key life-history traits such as age at first reproduction, and suggest that the trade-off between reproduction and self-maintenance might be mediated by the cumulative deleterious effect of ROS.

Aging↗
PubMed2005

Different patterns of selection on the nuclear genes IRBP and DMP-1 affect the efficiency but not the outcome of phylogeny estimation for didelphid marsupials.

Selection at the protein-level can influence nucleotide substitution patterns for protein-coding genes, which in turn can affect their performance as phylogenetic characters. In this study, we compare two protein-coding nuclear genes that appear to have evolved under markedly different selective constraints and evaluate how selection has shaped their phylogenetic signal. We sequenced 1,100+ bp of exon 6 of the gene encoding dentin matrix protein 1 (DMP1) from most of the currently recognized genera of New World opossums (family: Didelphidae) and compared these data to an existing matrix of sequences from the interphotoreceptor retinoid-binding protein gene (IRBP) and morphological characters. In comparison to IRBP, DMP1 has far fewer sites under strong purifying selection and exhibits a number of sites under positive directional selection. Furthermore, selection on the DMP1 protein appears to conserve short, acidic, serine-rich domains rather than primary amino acid sequence; as a result, DMP1 has significantly different nucleotide substitution patterns from IRBP. Using Bayesian methods, we determined that DMP1 evolves almost 30% faster than IRBP, has 2.5 times more variable sites, has less among-site rate heterogeneity, is skewed toward A and away from CT (IRBP has relatively even base frequencies), and has a significantly lower rate of change between adenine and any other nucleotide. Despite these different nucleotide substitution patterns, estimates of didelphid relationships based on separate phylogenetic analyses of these genes are remarkably congruent whether patterns of nucleotide substitution are explicitly modeled or not. Nonetheless, DMP1 contains more phylogenetically informative characters per unit sequence and resolves more nodes with higher support than does IRBP. Thus, for these two genes, relaxed functional constraints and positive selection appear to improve the efficiency of phylogenetic estimation without compromising its accuracy.

Amino Acid Sequence↗
PubMed2000

Carcinoma Arising in Microglandular Adenosis: An Immunohistochemical Analysis of 20 Intraepithelial and Invasive Neoplasms.

Microglandular adenosis (MGA) of the breast is an uncommon, benign lesion that may mimic invasive carcinoma and has recently been recognized as having significant premalignant potential. When carcinomas arise in MGA, there is often a transition from ordinary MGA to atypical MGA (AMGA) to carcinoma. Nineteen cases of carcinoma arising in MGA are reported: 7 invasive carcinomas, 7 intraductal carcinomas (DCIS), and 5 with both invasive and intraductal carcinoma. A single case of AMGA without carcinoma is also reported. The 20 patients ranged in age from 36 to 81 years (mean 52). The most common clinical presentation was either a palpable mass (13 patients) or a mammographic abnormality (4 patients). All 20 cases contained AMGA, and in some cases AMGA was the predominant lesion. In 18 of the 19 cases with carcinoma, there was a clear transition from AMGA to the carcinoma. Twelve cases contained ordinary MGA, but in only 2 cases was MGA a prominent component of the lesion. In contrast to ordinary MGA, the glands of AMGA were more irregularly shaped, closely packed, and cytologically atypical and tended to lack secretions. A solid, occlusive proliferation of cells in the tubules was seen in 10 cases. All 12 examples of in situ carcinoma were either grade 2 or 3 and typically showed a solid proliferation of severely atypical cells within the glands; a cribrifrom pattern was also present in 1 case. The invasive carcinomas were morphologically diverse and included 2 with a basaloid morphology and 2 metaplastic carcinomas. Various immunostains were performed, and each lesion (AMGA, in situ, and invasive carcinoma) was separately assessed for immunoreactivity. As expected, S-100 was positive in the vast majority of AMGA and in situ carcinomas and in all 12 invasive carcinomas. S-100beta was also positive in the majority of cases although the staining was weaker. Laminin and type IV collagen highlighted the basement membrane around the AMGA and in situ carcinoma and are useful stains in difficult cases. Except for a single case, ER and PR were negative in all lesions. Cytokeratin 7 (CK 7) was positive, while cytokeratin 20 (CK 20) was negative in all cases. Immunostains for CK903 showed no reactivity in any of the invasive carcinomas, in situ carcinomas, or atypical MGA but was focally present in the associated MGA in 2 of the 8 cases studied. Immunostains for MIB-1 and p53 were semiquantitatively assessed and both were positive in AMGA but tended to show a more intense staining in the carcinomas. Five cases were also studied for immunoexpression of alpha-1 antitrypsin (AAT), alpha-1 antichymotrypsin (ACTP), lysozyme, and salivary gland amylase. All 5 invasive carcinomas were positive for ACTP, though the staining was very focal in about 10% of the cells in a basaloid carcinoma. The in situ carcinoma as well as the AMGA in 4 of the 5 cases were positive for ACTP. Three of the 5 invasive carcinomas were positive for AAT in 10% to 40% of the cells. The most intense positivity for AAT and ACTP was in cells with coarsely granular apocrine appearance evident in 2 of the 5 cases. Four of the 5 invasive carcinomas were positive for lysozyme in 10% to 50% of the cancer cells; the in situ carcinoma and the associated AMGA showed similar immunoreaction in each case. None of the 5 cases showed convincing positivity for salivary gland amylase. The MGA in all 5 cases was negative for AAT and ACTP; the MGA in 1 of the 5 cases was positive for lysozyme. This study confirms the potential of MGA to develop into an invasive carcinoma, more clearly defines the features of AMGA, highlights the importance of AMGA in the evolution of carcinoma from MGA, and expands our knowledge of the immunophenotype of AMGA and the carcinomas arising from it. The diagnostic criteria briefly noted previously for diagnosis of AMGA and carcinoma arising in MGA are expanded and formally proposed. Int J Surg Pathol 8(4):303-315, 2000

Journal Article↗
PubMed2005

Evolutionary clues to eukaryotic DNA clamp-loading mechanisms: analysis of the functional constraints imposed on replication factor C AAA+ ATPases.

Ring-shaped sliding clamps encircle DNA and bind to DNA polymerase, thereby preventing it from falling off during DNA replication. In eukaryotes, sliding clamps are loaded onto DNA by the replication factor C (RFC) complex, which consists of five distinct subunits (A-E), each of which contains an AAA+ module composed of a RecA-like alpha/beta ATPase domain followed by a helical domain. AAA+ ATPases mediate chaperone-like protein remodeling. Despite remarkable progress in our understanding of clamp loaders, it is still unclear how recognition of primed DNA by RFC triggers ATP hydrolysis and how hydrolysis leads to conformational changes that can load the clamp onto DNA. While these questions can, of course, only be resolved experimentally, the design of such experiments is itself non-trivial and requires that one first formulate the right hypotheses based on preliminary observations. The functional constraints imposed on protein sequences during evolution are potential sources of information in this regard, inasmuch as these presumably are due to and thus reflect underlying mechanisms. Here, rigorous statistical procedures are used to measure and compare the constraints imposed on various RFC clamp-loader subunits, each of which performs a related but somewhat different, specialized function. Visualization of these constraints, within the context of the RFC structure, provides clues regarding clamp-loader mechanisms--suggesting, for example, that RFC-A possesses a triggering component for DNA-dependent ATP hydrolysis. It also suggests that, starting with RFC-A, four RFC subunits (A-D) are sequentially activated through a propagated switching mechanism in which a conserved arginine swings away from a position that disrupts the catalytic Walker B region and into contact with DNA thread through the center of the RFC/clamp complex. Strong constraints near regions of interaction between subunits and with the clamp likewise provide clues regarding possible coupling of hydrolysis-driven conformational changes to the clamp's release and loading onto DNA.

Adenosine Triphosphatases↗