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PubMed2003

An increased expression of nucleolin is associated with a physiological nucleolar segregation.

Nucleolar segregation is the most striking cellular phenotypic feature of cold-acclimatized carp and depicts the cyclical reprogramming that the physiology of the fish undergoes between summer and winter, where a clear differential expression of some nucleolar related genes occurs. We characterized carp nucleolin, a nucleolar protein involved in multiple steps of ribosome biogenesis, and evaluated its expression upon fish acclimatization. We show that the carp cDNA deduced amino acid sequence exhibits the same tripartite structural organization found in other species. Nevertheless, we observed that nucleolin mRNA expression was strongly induced in the cold-adapted carp as was the nuclear protein content, assessed by immunocytochemistry in liver sections. The physiological up-regulation of nucleolin in the cold-acclimatized carp, where rRNA transcription and processing are depressed concomitantly with the nucleolus segregation, is consistent with the notion that nucleolin plays a fundamental role in repressing rRNA synthesis.

Acclimatization↗

PubMed1994

An N-methyl-D-aspartate receptor antagonist does not prevent eye-specific segregation in the ferret retinogeniculate pathway.

Recent studies have shown that electrical activity, particularly that mediated by NMDA receptors, has a profound effect on the development of specific neuronal connections. Blocking NMDA receptors in the ferret's lateral geniculate nucleus prevents the segregation of retinal afferents into ON and OFF sublaminae. We have now examined the involvement of NMDA receptors in the separation of afferents from the two eyes that occurs in the lateral geniculate nucleus several weeks earlier in development. Blockade of NMDA receptor activity does not appear to interfere with this eye-specific segregation.

Animals↗

PubMed1997

Object segregation in 8-month-old infants.

Two experiments examined 8-month-old infants' use of configural and physical knowledge in segregating three-dimensional adjacent displays. The infants in Experiment I saw two identical yellow octagons standing side by side: in the test events, a hand grasped the right octagon and pulled it to the side. The infants looked reliably longer when the octagons moved apart than when they moved together, suggesting that the infants (a) perceived the octagons as a single unit and hence (b) expected them to move together and were surprised when they did not. The infants in Experiment 2 saw a yellow cylinder and a blue box: a hand grasped the cylinder and pulled it to the side. The infants looked reliably longer when the box moved with the cylinder than when the box remained in place, suggesting that they (a) viewed the cylinder and box as distinct units and thus (b) expected the cylinder to move alone and were surprised when it did not. These results indicate that, by 8 months of age, infants use configural knowledge when organizing adjacent displays: they expect similar parts to belong to the same unit and dissimilar parts to belong to distinct units. Additional results revealed that 8-month-old infants' interpretation of displays is affected not only by configural but also by physical consideration. Thus, infants in Experiment 1 who saw a thin blade lowered between the octagons viewed them as two rather than as one unit. Similarly, infants in Experiment 2 who saw the cylinder lying above instead of on the apparatus floor perceived the cylinder and box as one rather than two units. These results indicate that 8-month-old infants bring to bear their knowledge of impenetrability and support when parsing adjacent displays. Furthermore, when faced with two conflicting interpretations of a display, one suggested by their configural and one by their physical knowledge, infants allow the latter to supersede the former. Together, these findings suggest that, by 8 months of age infants approach to segregation is fundamentally similar to that of adults.

Adult↗

PubMed2003

Cadherin-mediated cell adhesion and tissue segregation: qualitative and quantitative determinants.

It is widely held that segregation of tissues expressing different cadherins results from cadherin-subtype-specific binding specificities. This belief is based largely upon assays in which cells expressing different cadherin subtypes aggregate separately when shaken in suspension. In various combinations of L cells expressing NCAM, E-, P-, N-, R-, or B-cadherin, coaggregation occurred when shear forces were low or absent but could be selectively inhibited by high shear forces. Cells expressing P- vs E-cadherin coaggregated and then demixed, one population enveloping the other completely. To distinguish whether this demixing was due to differences in cadherin affinities or expression levels, the latter were varied systematically. Cells expressing either cadherin at a lower level became the enveloping layer, as predicted by the Differential Adhesion Hypothesis. However, when cadherin expression levels were equalized, cells expressing P- vs E-cadherin remained intermixed. In this combination, "homocadherin" (E-E; P-P) and "heterocadherin" (E-P) adhesions must therefore be of similar strength. Cells expressing R- vs B-cadherin coaggregated but demixed to produce configurations of incomplete envelopment. This signifies that R- to B-cadherin adhesions must be weaker than either "homocadherin" adhesion. Together, cadherin quantity and affinity control tissue segregation and assembly through specification of the relative intensities of mature cell-cell adhesions.

Animals↗

PubMed2003

Membrane segregation and downregulation of raft markers during sarcolemmal differentiation in skeletal muscle cells.

Muscle contraction implies flexibility in combination with force resistance and requires a high degree of sarcolemmal organization. Smooth muscle cells differentiate largely from mesenchymal precursor cells and gradually assume a highly periodic sarcolemmal organization. Skeletal muscle undergoes an even more striking differentiation programme, leading to cell fusion and alignment into myofibrils. The lipid bilayer of each cell type is further segregated into raft and non-raft microdomains of distinct lipid composition. Considering the extent of developmental rearrangement in skeletal muscle, we investigated sarcolemmal microdomain organization in skeletal and smooth muscle cells. The rafts in both muscle types are characterized by marker proteins belonging to the annexin family which localize to the inner membrane leaflet, as well as glycosyl-phosphatidyl-inositol (GPI)-anchored enzymes attached to the outer leaflet. We demonstrate that the profound structural rearrangements that occur during skeletal muscle maturation coincide with a striking decrease in membrane lipid segregation, downregulation of annexins 2 and 6, and a significant decrease in raft-associated 5'-nucleotidase activity. The relative paucity of lipid rafts in mature skeletal in contrast to smooth muscle suggests that the organization of sarcolemmal microdomains contributes to the muscle-specific differences in stimulatory responses and contractile properties.

Annexins↗

PubMed1980

Lipid segregation from the maturing erythroid cell membrane.

Vesicles attached to the cell membrane of enucleating normoblasts and reticulocytes are considered indicative of the segregation of plasmalemmal components. The vesicles are obviously free from haemoglobin. They bind cationized ferritin and autologous immunoglobulin G. This segregation of plasmalemmal constituents is suggested to be one line of erythroid cell maturation.

Animals↗

PubMed1991

Segregation analysis and genetic counseling when both parents carry balanced chromosomal translocations.

OBJECTIVE: To assess the risk of chromosomally abnormal offspring and discuss counseling approach when both parents carry balanced translocations. DESIGN: Theoretical segregation analysis is performed and use of empiric data is used in genetic counseling. SETTING: Patients are referred to Division of Reproductive Genetics at the University of Tennessee, Memphis. PATIENTS, PARTICIPANTS: The mother, heterozygous for reciprocal translocation 46,XX, rcp(7;13)(p21;q22) and father, heterozygous for Robertsonian translocation 45,XY,rob(13q;14q) were referred for genetic counseling concerning risks of chromosomally abnormal offspring. INTERVENTIONS: Segregation analysis, genetic counseling, and chorionic villus sampling. MAIN OUTCOME MEASURE(S): A cumulative risk was derived to use for counseling purposes. Cytogenetics using GTG-banding was performed on cultured chorionic villus cells. RESULTS: Theoretical risk of this couple having chromosomally abnormal offspring was 40.5%. On the basis of empirical data and risk factors inherent in the specific translocations, the maternal contribution at midtrimester was 3.5%; the paternal contribution was 1% to 2%. The sum of these risks was used in counseling. CONCLUSIONS: The fetus was found to be 46,XY,rcp(7;13)(p21;q22).

Abortion, Habitual↗

PubMed2003

A sexual selection theory longitudinal analysis of sexual segregation and integration in early adolescence.

The three objectives in this longitudinal study were motivated by sexual selection theory. The theory specifies the role of sexually segregated groups and the effects of dominance in male groups and relational/indirect aggression in female groups for heterosexual relationships. Using a multi-method, multi-informant, longitudinal design we studied youngsters (N=138) across their first two years of middle school. First, we examined the nature of change in segregation and dating popularity across two years during early adolescence. Second, a model derived from sexual selection theory is tested to explain the ways in which boys and girls are nominated for hypothetical dates (dating popularity). Third, we examined the role of "poke and push courtship" behavior in boys' and girls' dating popularity. Results indicate that although groups did not become more integrated with time, changes in peer group sexual integration co-varied dynamically with dating popularity. Secondly, dominance-related strategies were more important for boys than girls in dating popularity whereas indirect, or relational, aggression strategies were more important for girls than boys. Third, "poke and push courtship" behaviors did not influence peer group integration or dating.

Adolescent↗

PubMed1990

Analysis of a model for minichromosome segregation in Escherichia coli.

The present article contains a theoretical, quantitative analysis of the implications of the Helmstetter-Leonard model (1987, J. molec. Biol. 197, 195-204.) for the segregation of chromosomal DNA in Escherichia coli, on the expected copy-number distribution of minichromosomes in a culture in steady-state exponential growth. According to the model, two determinants are involved in the mechanism of chromosome segregation: a partition system that assures the equal allotment of chromosomes between daughter cells at cell division, and a locus within the minimal oriC region that specifies the attachment site of the chromosomes to the cell envelope at initiation of replication. There are many parameters that must be taken into account in such a study, and since some of them are probabilistic in nature, a strictly analytical approach is not feasible and we had to resort to computer simulation. A wide range of parameter values was tested, in all combinations. The minichromosome copy-number distributions obtained all had a prominent mode equal to the number of oriC binding sites and their main features were determined essentially by that and very little by any of the other parameters of the model. In order to avoid the unrealistic situation in which this one feature completely dominates the results, the original model was modified so that each individual minichromosome is no longer required to replicate during every cell generation, by introducing a limit to the number of unsuccessful attempts to locate a suitable binding site. The copy-number distributions predicted by this version of the model are quantitatively and qualitatively very different and depend on all the components of the model. The simulation results are sufficiently well-behaved to allow consideration as to whether a particular empirical minichromosome copy-number distribution--when such data become available--could in fact be governed by the proposed model; it may even be possible to get a rough estimate for the different parameters involved.

Computer Simulation↗

PubMed1998

A global process in motion segregation.

Observers viewed sparse random dot cinematograms in which the moving dots were confined to eight windows. The motions in seven of the windows were consistent with a global flow pattern, while the direction of motion in the eighth window deviated from this pattern. The observer's task was to determine which of the eight windows contained the inconsistent motion. The task was performed on two types of global flow patterns: spirals, which appear rigid, and deformations, which appear highly non-rigid. Although these patterns produce qualitatively different global percepts, they are exactly matched in their local velocities and velocity differences. Observers were better able to locate an inconsistent motion in spiral patterns than in deformation patterns, indicating that they were using more than just local motion information to find the target. This result is taken as indirect support for a segregation process that involves fitting the stimulus with a global motion pattern and segregating motions inconsistent with this pattern.

Female↗

PubMed1998

Figure/ground segregation from temporal delay is best at high spatial frequencies.

Two experiments investigated the role of spatial frequency in performance of a figure/ground segregation task based on temporal cues. Figure orientation was much easier to judge when figure and ground portions of the target were defined exclusively by random texture composed entirely of high spatial frequencies. When target components were defined by low spatial frequencies only, the task was nearly impossible except with long temporal delay between figure and ground. These results are inconsistent with the hypothesis that M-cell activity is primarily responsible for figure/ground segregation from temporal delay. Instead, these results point to a distinction between temporal integration and temporal differentiation. Additionally, the present results can be related to recent work on the binding of spatial features over time.

Adult↗

PubMed2002

Biofilm development and bed segregation in a methanogenic fluidized bed reactor.

Bacterial biofilm growth on a pilot lab scale anaerobic fluidized bed bioreactor under mesophilic conditions is analyzed in this paper. Biolite was used as substratum and the system was fed with acetic acid as sole carbon source. Bed expansión was maintained around 40%. It was observed that the decrease of the expansion provoked a biomass increase in the reactor and the decrease of the removal rate of organic matter. This can be explained by a mass transfer limitation phenomenon. Volatile fatty acids accumulated within the system when the expansion of the fluidized bed was lower than 10%. An initial bed segregation was observed. Biomass adhesion and growth influenced bioparticle size and density, which contributed to further bed segregation. Biomass concentration in the bottom part of the bed showed higher values than in the upper levels. On the other hand, biofilm density increased towards the reactor bottom, wherein it showed the highest values. Methanogenic tests were conducted using acetic, propionic and butyric acids. These assays indicated that total activity was higher in bioparticle sampled from upper reactor levels. This was explained by the lower biofilm density values in this zone and mass transfer limitation phenomena. Moreover, biomass was unable to degrade acids different from acetic while performing the activity tests. This was probably due to the fact that acetic acid was the sole carbon source fed to the reactor.

Acetic Acid↗

PubMed1997

Chromosome and low copy plasmid segregation in E. coli: visual evidence for distinct mechanisms.

We have investigated DNA segregation in E. coli by inserting multiple lac operator sequences into the chromosome near the origin of replication (oriC), in the hisC gene, a terminus marker, and into plasmids P1 and F. Expression of a GFP-LacI fusion protein allowed visualization of lac operator localization. oriC was shown to be specifically localized at or near the cell poles, and when duplicated, one copy moved to the site of new pole formation near the site of cell division. In contrast, P1 and F localized to the cell center and on duplication appeared to move rapidly to the quarter positions in the cell. Our analysis suggests that different active processes are involved in movement and localization of the chromosome and of the two plasmids during segregation.

Cell Cycle↗

PubMed1996

Chromatid segregation at anaphase requires the barren product, a novel chromosome-associated protein that interacts with Topoisomerase II.

We have isolated a Drosophila gene, barren (barr), required for sister-chromatid segregation in mitosis. barr encodes a novel protein that is present in proliferating cells and has homologs in yeast and human. Mitotic defects in barr embryos become apparent during cycle 16, resulting in a loss of PNS and CNS neurons. Centromeres move apart at the metaphase-anaphase transition and Cyclin B is degraded, but sister chromatids remain connected, resulting in chromatin bridging. This phenotype is similar to that described in TOP2 mutants in yeast. Barren protein localizes to chromatin throughout mitosis. Colocalization and biochemical experiments indicate that Barren associates with Topoisomerase II throughout mitosis and alters the activity of Topoisomerase II. We propose that this association is required for proper chromosomal segregation by facilitating the decatenation of chromatids at anaphase.

Anaphase↗

PubMed1980

Segregation of developmental potential in early embryos of Caenorhabditis elegans.

We have followed the appearance of differentiation markers in cleavage-inhibited and uninhibited early blastomeres of C. elegans and have compared the cleavage patterns of blastomeres in partial and complete embryos. The results indicate that at least some primary differentiation of embryonic cells is determined by internal factors that segregate in early cleavages, whereas patterns of cleavage are dictated by both internally segregating determinants and external cues.

Animals↗

PubMed1988

SPA1: a gene important for chromosome segregation and other mitotic functions in S. cerevisiae.

Human autoantibodies that recognize the spindle poles of mammals, plants, and insects were found to recognize two antigens in yeast. One of these proteins, called SPA1 (for Spindle Pole Antigen), is antigenically related to the spindle poles of a diverse set of organisms. The gene encoding SPA1 was cloned by immunoscreening a lambda gt11 yeast genomic DNA expression library with autoantibody probes. Mutational analysis of the SPA1 gene demonstrates that it is important for cell growth, chromosome segregation, and other cellular processes; spa1 mutants are viable but grow poorly at 30 degrees C, missegregate chromosomes at an increased frequency, and often contain deformed spindles. A significant fraction of spa1 mutant cells contain two or more nuclei, and others contain none; these abnormal cells may arise through a nuclear migration defect. Thus SPA1 represents a new fidelity gene that is important for chromosome segregation and other mitotic functions.

Autoantibodies↗

PubMed2000

Mitochondrial genotype segregation and effects during mammalian development: applications to biotechnology.

Mitochondria are endosymbiotic organelles responsible for energy production in practically every eukaryotic cell. Their uniparental fashion of inheritance, maternally inherited in mammals, and the homogeneity of mitochondrial DNA (mtDNA) within individuals and matrilineages, are biological phenomena that remain unexplained. This paper reviews some of the recent findings on mitochondrial influences on the manner in which embryos develop and how their genotypes are inherited in mammals, with particular emphasis on the genetic "bottleneck" effect. Animal models carrying a mix of mtDNAs (heteroplasmic) have been produced by karyoplast and cytoplast transplantation to analyze the segregation patterns at different stages during embryogenesis, in fetuses and offspring. Comparisons performed between murine and bovine reveal interesting changes in segregation and replication of transplanted mtDNAs. We have recently obtained Bos indicus and Bos taurus fetuses and calves from embryos reconstructed using enucleated polymorphic oocytes of Bos taurus origin. These and other findings on mitochondrial biology will have important implications in determining the cytoplasmic genotype of clones and in the preservation of endangered breeds and species.

Animals↗

PubMed2003

Identification of coronaviruses in dogs that segregate separately from the canine coronavirus genotype.

The genetic diversity of 16 canine coronavirus (CCoV) samples is described. Samples were obtained from pups infected naturally living in different areas. Sequence data were obtained from the M gene and pol1a and pol1b regions. The phylogenetic relationships among these sequences and sequences published previously were determined. The canine samples segregated in two separate clusters. Samples of the first cluster were intermingled with reference strains of CCoV genotype and therefore could be assigned to this genotype. The second cluster segregated separately from CCoV and feline coronavirus genotypes and therefore these samples may represent genetic outliers. The reliability of the classification results was confirmed by repeating the phylogenetic analysis with nucleotide and amino acid sequences from multiple genomic regions.

Amino Acid Sequence↗