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PubMed1993

Giant and binucleate trophoblast cells of mammals.

The cellular origin, structure, and function of trophoblastic giant cells (GC) and binucleate cells (BNC) are reviewed. Mammals in which these cells have received the greatest attention include rodents, rabbits, and humans (GCs), and ruminants and equids (BNCs). In almost all cases these cells arise from the cytotrophoblast. All are large cells and contain either two diploid nuclei (BNCs), multiple nuclei (human placental bed GCs), or single nuclei with amplified DNA content (rodent and rabbit GCs). Giant and binucleate cells typically exhibit the capacity for migration or invasion, although the degree of migratory activity varies between species. While most end up within, or at the interface with, endometrial tissue, in some instances the GCs or BNCs contribute directly to the interhemal membrane of the placenta. Hormone production is a property which most GC-BNC populations have in common. Lactogen or gonadotropin has been documented in almost all cells of this type examined to date, and in some animals they are also steroidogenic (e.g., rats and sheep). In spite of some common features, both structural and functional differences remain and it is suggested that use of terms such as mononuclear giant cells, multinucleate giant cells, and binucleate cells be continued rather than assuming that these cells are all members of a single trophoblastic subtype.

Animals↗
PubMed2006

The tri-segmented limbs of therian mammals: kinematics, dynamics, and self-stabilization--a review.

The evolution of therian mammals is to a large degree marked by changes in their motion systems. One of the decisive transitions has been from the sprawled, bi-segmented to the parasagittal, tri-segmented limb. Here, we review aspects of the tri-segmented limb in locomotion which have been elucidated in our research groups in the last 10 years. First, we report the kinematics of the tri-segmented therian limb from mouse to elephant in order to explore general principles of the therian limb configuration and locomotion. Torques will be reported from a previous paper (Witte et al., 2002. J Exp Biol 205:1339-1353) for a better understanding of the anti-gravity work of all limb joints. The stability of a limb in z-configuration will be explained and its advantage with respect to other potential solutions from modeling will be discussed. Finally, we describe how the emerging concept of self-stability can be explained for a tri-segmented leg template and how it affects the design of the musculoskeletal system and the operation of legs during locomotion. While locomotion has been considered as mainly a control problem in various disciplines, we stress the necessity to reduce control as much as possible. Central control can be cheap if the limbs are "intelligent" by means of their design. Gravity-induced movements and self-stability seem to be energy-saving mechanisms.

Animals↗
PubMed1985

Use of the term "trophoblast" for tissues in therian mammals.

Use of the term "trophoblast" in descriptions of therian (marsupial and eutherian) mammals has caused confusion because of misinterpretations of blastular homologies and because of imprecise application in functional versus ontogenetic-phylogenetic senses. Marsupials follow the plan of early development characteristic of noneutherian amniotes. Eutherians, in contrast, are unique in the early determination of presumptive embryonic versus extraembryonic cells through formation of inner cell mass versus trophoblastic (or trophectodermal) tissues, respectively. No cellular unit of the eutherian blastula is recognizable unequivocally as the homologue of a specific part of the protodermal marsupial blastula; progressive deletion of innovative but phylogenetically older ontogenetic steps probably figured importantly in the evolution of eutherian early embryogenesis. Because of marked differences in mode of formation and in cellular fates, homology of the blastocoel between marsupials and eutherians is questioned. It is suggested that use of the term "trophoblast" be restricted to eutherians in discussions of ontogenesis or phylogenesis, and be deemphasized in the functional sense (i.e., fetal-maternal exchanges) for marsupials, in favor of the more appropriate tissue terms of "choriovitelline" and "chorioallantoic" membranes. Integral to the origin of the eutherian style of embryogenesis was the evolution during Cretaceous time of neomorphic, extraembryonic tissues (i.e., trophoblast) having physiological properties that allowed the unique combination of intimate apposition of fetal and maternal tissues and circulatory systems, along with sustained, active morphogenesis. Marsupials have not achieved such a combination.

Animals↗
PubMed1988

Trophoblast concept as applied to therian mammals.

Available evidence provides little support for a recent proposal that the term "trophoblast" be applied solely to eutherian mammals. Arguments for such a restricted usage are based on a dichotomous interpretation of therian reproduction that underestimates the developmental, structural, and functional diversity of trophoblastic tissues occurring within the infraclass Eutherian. The occurrence of developmental patterns that are phenotypically intermediate between those of commonly studied eutherians and metatherians suggests that blastocyst development is not fundamentally different in marsupials and eutherians. The trophoblast of marsupials accomplishes most or all of the major functions of the eutherian trophoblast, including maternal-fetal physiological exchange, implantation, contribution to placental membranes, steroid metabolism, and possibly, immunological protection of the conceptus. Furthermore, application of the term "trophoblast" to marsupials is consistent with present and past usage, as well as with the original definition and etymological derivation of the term. Therefore, we recommend that the term "trophoblast" continue to be applied in a functional-morphological sense to the appropriate extraembryonic tissues of marsupials. Such use of functional (rather than taxonomic) criteria for application of this term avoids biasing interpretations of mammalian reproductive evolution.

Animals↗
PubMed2002

Protamine 1: protamine 2 stoichiometry in the sperm of eutherian mammals.

We have compared the relative proportion of protamine 1 (P1) and protamine 2 (P2) bound to DNA in the sperm of a variety of eutherian mammals to obtain insight into how these two proteins interact in sperm chromatin. Gel electrophoresis (combined with microdensitometry) and high performance liquid chromatography (HPLC) were used to determine the content of the two protamines, and the identity of each protein was confirmed by amino-terminal sequencing or amino acid analysis. The sperm of all species examined contained P1, but P2 was found to be present only in certain species. Unlike the fixed ratio of core histones that package DNA into nucleosomes in all somatic cells, the proportion of P2 present in mature sperm was found to be continuously variable from 0 to nearly 80%. These results show that P1 and P2 do not interact with each other or DNA to form a discrete complex or subunit structure that is dependent upon particular P1/P2 stoichiometries. Data obtained from a number of closely and distantly related species also indicate that while the P2 content of sperm chromatin is allowed to vary over a wide range during the course of evolution, the relative proportion of P1 and P2 are tightly regulated within a genus.

Animals↗
PubMed1990

Conformational flexibility of a scorpion toxin active on mammals and insects: a circular dichroism study.

Three scorpion toxins have been analyzed by circular dichroism in water and in 2,2,2-trifluoroethanol (TFE) solutions. These toxins were chosen because they are representative of three kinds of pharmacological activities: (1) toxin AaH IT2, an antiinsect toxin purified from the venom of Androctonus australis Hector, which is able to bind to insect nervous system preparation, (2) toxin Css II, from the venom of Centruroides suffusus suffusus, which is a beta-type antimammal toxin capable of binding to mammal nervous system preparation, and (3) the toxin Ts VII from the venom of Tityus serrulatus, which is able to bind to both types of nervous systems. In order to minimize bias, CD data were analyzed by a predictive algorithm to assess secondary structure content. Among the three molecules, Ts VII presented the most unordered secondary structure in water, but it gained in ordered forms when solubilized in TFE. These results indicated that the Ts VII backbone is the most flexible, which might result in a more pronounced tendency for this toxin molecule to undergo conformational changes. This is consistent with the fact that it competes with both antiinsect and beta-type antimammal toxins for the binding to the sodium channel.

Amino Acid Sequence↗
PubMed1991

Review of drug-induced limb defects in mammals.

The objective of this paper was to illustrate the spectrum of possible limb malformations in mammals resulting from drug exposure. A bibliography of 171 papers from 20 journals was generated from which pertinent data (drug used, limb defects reported, predominant defect location) were tabulated. These data should provide a basis for predictions about types of defects that might be expected in further studies and for judging postulated drug-induced human limb defects. However, direct extrapolation to humans is inappropriate. The following trends were observed: 1) Distal limb defects (autopod) are almost twice as common as proximal limb defects (stylopod and zygopod). 2) Ectrodactyly is the single most common type of limb defect, accounting for over half of the autopod defects. 3) Ectrodactyly is almost twice as common in the hindlimb as in the forelimb. 4) Postaxial ectrodactyly is over twice as common as preaxial ectrodactyly in the forelimb, but preaxial ectrodactyly is four times more common in the hindlimbs. 5) Polydactyly occurs with approximately equal frequency in forelimbs and hindlimbs, and preaxial polydactyly is most common in both fore and hindlimbs. 6) Polymelia (supernumerary limbs) occurred in one case, and may have been a spurious result. 7) Either transverse hemimelia is greatly underreported in teratology studies or it essentially does not occur. We have concluded that, at least in some cases, acetazolamide, adenine, 1,7-dimethylxanthine, and xanthine derivative aminophylline, retinoic acid, acetoxy-methyl-methylnitrosamine, aspirin, and cadmium can all cause unilateral defects.

Abnormalities, Drug-Induced↗
PubMed1998

Genomic organization of a receptor from sea anemones, structurally and evolutionarily related to glycoprotein hormone receptors from mammals.

Cnidarians (e.g., sea anemones and corals) are the lowest animal group having a nervous system. Previously, we cloned a receptor from sea anemones that showed a strong structural similarity to the glycoprotein hormone (TSH, FSH, LH/CG) receptors from mammals. Here, we determine the genomic organization of this sea anemone receptor. The receptor gene contains eight introns that are all localized within a region coding for the large extracellular N terminus. These introns occur at the same positions and have the same intron phasing as eight introns in the genes coding for the mammalian glycoprotein hormone receptors, indicating that the cnidarian and mammalian receptor genes are evolutionarily related. As with the mammalian receptor genes, the sea anemone receptor gene does not contain introns in the region coding for the transmembrane and intracellular domains. Southern blot analyses show that the cnidarian receptor is coded for by a single gene.

Animals↗
PubMed1996

Relationship between the monosomy X phenotype and Y-linked ribosomal protein S4 (Rps4) in several species of mammals: a molecular evolutionary analysis of Rps4 homologs.

Two isoforms of the human ribosomal protein S4 gene, RPS4X and RPS4Y, are located on the X and Y chromosomes. It has been postulated that haploinsufficiency of these genes may contribute to Turner syndrome. We show here that several animal species that show the Turner-like phenotype on monosomy X have no Y-linked Rps4 homolog. There may be another gene(s) that contributes to abnormal phenotypes of monosomy X. Molecular evolutionary analysis shows that the Y-linked and RPS4X-related homologs diverged prior to the radiation of placental mammals and evolved independently. Furthermore, the functional constraints against the RPS4X-related homologs are much stronger than those against the Y-linked homologs.

Animals↗
PubMedDate not supplied

Mammals and rainfall: paleoecology of the middle Miocene at La Venta (Colombia, South America).

A comparison of the species richness and macroniche composition of diet, locomotor and body-size classes among 16 nonvolant mammalian faunas in tropical South America reveals numerous significant positive correlations with rainfall. In particular, significant and strong positive correlations with rainfall are found in 18 attributes, including the number of nonvolant mammal species, number of primate species, number of frugivores, primary consumers, arborealists, and the number of species between 100 g to 10 kg in body weight. Estimates of annual rainfall derived from least-squares and polynomial regressions and principal components analysis yield a modal estimate of between 1500 and 2000 mm annual rainfall for the Monkey Beds assemblage at La Venta. This level of rainfall is associated today with the transition between savanna and forest environments in lowland equatorial South America. Paleontological evidence strongly suggests the presence of forest biotopes at La Venta. Paleontologic and sedimentologic evidence together indicate a dynamic and heterogeneous riparian mosaic associated with the shifting course of meandering rivers. Faunal evidence also suggests that habitat heterogeneity and canopy discontinuity extended into the interfluvial area. Seasonal rainfall was probably only of secondary importance in shaping the structural and spatial configuration of the dominantly forested mosaic habitat at La Venta. The fossil record is not consistent with the presence of extensive primary or undisturbed, continuous-canopy, evergreen tropical rainforest. The reconstructed middle Miocene environment at La Venta differs significantly from modern environments of similar geography on the piedmont east of the Andes at the same latitude. This in turn suggests that the extensive evergreen rainforests of the upper Amazonian piedmont that today receive more than 4000 mm of rainfall may post-date the initiation of Andean uplift.

Animals↗
PubMed2000

Evolutionary inventions and continuity of CORE-SINEs in mammals.

We characterized short interspersed elements (SINEs), of the CORE-suprafamily in egg-laying (monotremes), pouched (marsupials) and placental mammals. Five families of these repeats distinguished by the presence of distinct LINE-related 3'-segments shared tRNA-like promoter and the central core region. The putative active elements were reconstructed from the alignment of genomic repeats representing molecular fossils of sequences that amplified in the past and since then underwent multiple mutations. Their mode of proliferation by retroposition was indicated by the presence of: (1) internal RNA PolIII promoter; (2) simple sequence repeated tail; (3) direct repeats; and (4) subfamilies recording the evolution of elements. The copy number of CORE-SINEs in placental genomes was estimated at about 300,000; they were highly divergent and apparently ceased to amplify before radiation of these lineages. On the other hand, among almost half a million fossil elements present in marsupials and monotremes, the youngest subfamilies could still be retropositionally active. CORE-SINEs terminate in sequence repeats of a few nucleotides similar to their 3'-segment LINE-homologues, CR1, L2 and Bov-B. These three LINE elements fall into clades distinct from that of L1 elements which, similar to their co-amplifying SINEs, end in a poly(A) tail. We propose a model in which new CORE-families, with distinct 3'-segments, are created at the RNA level due to template switching between LINE and CORE-RNA during reverse transcription. The proposed mechanism suggests that such an adaptation to the changing amplification machinery facilitated the survival and prosperity of CORE-elements over long evolutionary periods in different lineages.

Animals↗
PubMed1993

The time allometry of mammalian chewing movements: chewing frequency scales with body mass in mammals.

For a sample of 26 extant mammalian species, a significant relationship between body mass and chewing frequency was found, in which chewing frequency is proportional to body mass to the -0.128 power. This relationship is similar to previously published data relating stride frequency and body mass in quadrupedal mammals. It was also found that jaw length is proportional to body mass to the 0.312 power, which is consistent with geometric scaling of jaw length. The period of the chewing cycle was found to be proportional to jaw length to the 0.383 power. These results demonstrate that chewing frequency does not scale as metabolic rate, and support the suggestion that the natural frequency of the chewing rhythm may be derived from masses and lengths of the components of the masticatory apparatus alone.

Animals↗
PubMed1996

Genetic conflicts and the paradox of sex determination: three paths to the evolution of female intersexuality in a mammal.

That sex determining systems ever change is paradoxical but can be explained by noting that conflict between selfish elements and their modifiers will often cause a shift in sex determining strategy. The evolution of the novel sex determining system of moles (Talpa europaea and T. occidentalis) may, we argue, be an example of just such a process. Three different models for the evolution of female intersexuality are presented. These all attempt to account for (1) the fact that a few years ago populations of moles had high frequencies of sterile XX individuals that were either morphologically male or intersex (other XX individuals were normal females) and (2) that presently, the XX individuals in the same population are exclusively fertile intersexes that are functionally female; i.e. have follicle producing ovotestes. This case history is compared to that of the wood lemming and two similarities are discussed. First, in both cases it is noted that one end product could be approached from different routes. Second, selfish elements may be involved in the evolution of both systems. In general, it is suggested that XY sex determination, far from being resilient to evolutionary change, is vulnerable to take-over by selfish elements. This is particularly the case in mammals in which transplacental interactions could allow manipulation of sex determination in one foetus by another. This, we also suggest, is a good candidate explanation for the evolution of novel sex determination in Talpa.

Animals↗
PubMed1998

Molecular and morphological phylogenies of mammals: congruence with stratigraphic data.

Tests of a sample of 206 cladograms of mammals show that morphological data seem to predict phylogenies that match the known fossil record better than molecular trees. Three metrics that assess the rank order of branching points, the stratigraphic consistency of those nodes, and the ratio of ghost range to known range show a considerable diversity of values. Some published trees show excellent matching with fossil-record data; others show almost no correspondence whatsoever. Morphological trees are nearly twice as good as molecular trees in terms of matching of the rank orders of nodes and oldest fossils, while morphological trees are 10% better than molecular in terms of stratigraphic consistency of the nodes. The ratios of ghost range to known range are lower for molecular trees. Among the molecular trees, those based on gene data are considerably better than those based on protein sequences, at least in terms of the rank order of nodes and the stratigraphic consistency of nodes. Protein trees, however, were best of all in terms of minimizing the proportion of ghost range. These findings probably indicate real phenomena, but the match of molecular trees to the expectations of stratigraphy may improve as the study of molecular phylogeny matures.

Animals↗
PubMed1998

Highly congruent molecular support for a diverse superordinal clade of endemic African mammals.

A solution to higher level mammalian phylogeny is going to depend on the congruent establishment of superordinal groupings followed by a linking together of these clades. We present congruent and convincing evidence from four disparate nuclear protein coding genes and from a tandem alignment of the 12S-16S mitochondrial region, for a superordinal clade of endemic African mammals that includes elephant shrews, aardvarks, golden mole, elephants, sirenians, and hyraxes. Because of strong support for golden mole as part of this clade, the Insectivora are rendered paraphyletic or polyphyletic, with constrained monophyly of the insectivores judged significantly worse in the vast majority of tests. Branching arrangement within this clade remains highly uncertain; however, a tandem alignment of the protein coding genes suggests elephant shrew is the earliest African lineage. None of the individual data sets or combinations of data sets support the widely held view of a mirorder Tethytheria (Sirenia/Proboscidea), although only a tandem alignment of protein coding and mitochondrial loci significantly rejects this association. The majority of the data sets and analyses provide strong support for Caviomorpha as part of a monophyletic Rodentia.

Africa↗
PubMed2001

The initiation and regulation of Ca2+ signalling at fertilization in mammals.

The transition from oocyte to embryo in mammals is triggered by a series of calcium transients. There are two distinguishing features of this signal transduction pathway. First, it appears to be triggered by a cell fusion event between egg and sperm that allows the direct introduction of a factor that leads to the release of intracellular Ca2+. Second, it features a slow-frequency calcium oscillator (one transient every 10-20 min) that persists for 3-4 h. In this review I report on recent developments in our understanding of how the Ca2+ oscillations are started and on the regulation of the overall temporal organization. The review focuses on mammalian fertilization and (inevitably) it is fertilization in the mouse that will be predominantly discussed. Relevant and topical contributions from the excellent body of literature available on other species will be utilized where appropriate but extensive reviews can be found elsewhere [Stricker S A (1999) Comparative biology of calcium signaling during fertilization and egg activation in animals Dev Biol 211: 57-76; Jaffe et al., this issue].

Animals↗
PubMed2001

Photic entrainment of the circadian clock: from Drosophila to mammals.

Entrainment is as fundamental to an organism's circadian timing as are the molecular mechanisms involved in the functioning of the intracellular clock oscillator. In nature, one of the principle, although not the only, circadian entraining stimulus (Zeitgeber) is provided by the daily light--dark cycles. In animals, the visual processing apparatus alone is inadequate to accomplish the task of transducing circadian photic signals to the clockwork machinery. In fact, it is ever more appreciated by circadian biologists that organisms as divergent as plants and mammals have evolved a wonderfully complex array of partly redundant specializations which can guarantee the precise alignment of biological and environmental time. Research in circadian biology is cruising at such a rate that attempts to review the state of the art can only hope, at best, to provide a snapshot of the speeding cruiser from its wake. This paper will hopefully provide a reasonably sharp portrayal of what is at hand.

Animals↗
PubMed1985

Gene expression during oogenesis and oocyte development in mammals.

Mouse oocytes progress through early meiotic prophase during fetal life and reach the diplotene stage by birth. During prepubertal and reproductive life, oocytes are continuously selected to grow from the pool of small primordial oocytes. Growing oocytes reach full size in 2 weeks, and full-grown oocytes are present in rapidly enlarging follicles for about 5 days before meiotic maturation and ovulation. RNA synthesis during early meiotic prophase, as estimated from [3H]uridine incorporation followed by autoradiography and from electron microscopic analysis of nuclear components, proceeds at a moderate rate throughout except for a brief period in early pachytene when synthesis is low or absent. RNA synthesis continues in primordial oocytes at a moderate rate. Incorporation studies, electron microscopic analyses, and particularly measurements of ongoing RNA polymerase activity (completion of initiated chains as analysed in tissue sections) indicate a distinctly increased rate of synthesis during oocyte growth over that of primordial oocytes, followed by a decline in full-grown oocytes. During growth, this rate increases severalfold. The absolute rate of synthesis of heterogeneous nuclear RNA (using rRNA as a standard) during mid-growth is very rapid, but nevertheless still much lower than that in typical lampbrush chromosomes. Most of the hnRNA turns over with a half-life of about 20 min, as is typical in somatic cells. Newly synthesized mRNA-like RNA enters the cytoplasm at about one-half the rate of rRNA, and about one-third of the ribosomes and one-fourth of the mRNA appear in polysomes. In full-grown oocytes, the rate of synthesis falls distinctly, but a significant level of synthesis continues until it essentially ceases at breakdown of the germinal vesicle. During meiotic prophase, chromosomes are most compact at pachytene and unfold lateral projections as RNA synthesis increases in late pachytene-early diplotene. In primordial oocytes, the diplotene state of chromosomes is obvious in most mammals, but in rodents the chromosomes are more evenly dispersed and are said to be in a dictyate state, although they are still presumably in a diplotene configuration. The chromosome core, which is present in leptotene through early diplotene stages, apparently disappears in the dictyate stage.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗