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PubMed1983

Segregation of germline granules in early embryos of Caenorhabditis elegans: an electron microscopic analysis.

Using an improved fixation method for electron microscopy, we have found germline granules in Caenorhabditis elegans embryos shortly after fertilization and prior to the first cleavage. They are localized in the egg cytoplasm which becomes segregated into the posterior blastomere at the first cleavage. In the following divisions, the granules continue this pattern of asymmetric segregation and are ultimately segregated into the germline precursor cell. The granules are then symmetrically segregated into the germline cells.

Animals↗
PubMed1994

Regulation of yeast chromosome segregation by Ipl1 protein kinase and type 1 protein phosphatase.

Chromosome segregation is a complicated process that involves the coordinated functioning of a large number of cellular components. In this process, many proteins are activated and inactivated in a strict temporal order. While much progress has been made recently in the identification of structural components that are involved in chromosome segregation, relatively little is known about their regulation. We have investigated the chromosome segregation process in the budding yeast Saccharomyces cerevisiae. Our results indicate that this process absolutely requires a functional Ipl1 protein kinase. Upon inactivation of this protein kinase, yeast cells missegregate chromosomes severely and die within a single cell cycle. Furthermore, the inviability caused by a partial reduction in Ipl1 function can be rescued by perturbations that reduce type 1 protein phosphatase activity, thus suggesting that type 1 protein phosphatase acts in opposition to the Ipl1 protein kinase to insure the high fidelity of chromosome segregation in yeast cells. The purpose of this article is to describe some of our ongoing efforts to characterize Ipl1 and PP1 functions.

Aurora Kinases↗
PubMed1993

Perceptual ranking versus visual evoked potentials for different local features in texture segregation.

PURPOSE: To validate recent reports of specific visual evoked potentials associated with preattentive texture segregation (tsVEPs) and to quantitatively compare perceptual segregation strength and tsVEP amplitudes across different local features. METHODS: Four local features were selected: crossed vs noncrossed, line segments differing in orientation by 90 degrees, U-shapes differing in orientation by 90 degrees, and U-shapes differing in orientation by 180 degrees. The two variants of each local feature were spatially arranged in a checkerboard pattern; for the first three features this led to pop-out of a "preattentive checkerboard." In seven subjects, perceptual segregation strength was assessed using ranking, and tsVEPs were recorded in these and three additional subjects. RESULTS: Statistically significant tsVEPs were obtained for the features crossed vs noncrossed and 90 degrees-line segments. Ranking results and tsVEP amplitudes were highly correlated (P < 0.001); the order of perceptual ranking and the order of tsVEP amplitudes were identical; 180 degrees-U-shapes had lowest ranking, mean tsVEP amplitude was 0.1 microV, close to noise. Line segments had maximal ranking, tsVEP amplitude was 1.5 microV. CONCLUSIONS: The results suggest that tsVEPs quantitatively reflect the activity of cortical mechanisms involved in texture segregation across various features.

Adult↗
PubMed1996

Within birth cohort segregation analyses support recessive inheritance of body mass index in white and African-American families.

OBJECTIVE: We conducted segregation analyses of body mass index within birth cohort to determine whether previously reported support for recessive major gene inheritance in white and African-American families could have been due to higher rates of obesity in offspring than in parents, which are caused by temporal increases in obesity in recent decades. DESIGN: Segregation analysis of family data. MEASUREMENT: The body mass index (BMI), adjusted for effects of gender, linear and non-linear effects of age, education and occupation of head of household, and clinic from which family was ascertained. RESULTS: Segregation analysis results support a recessive mode of major gene inheritance of body mass index, even though we restricted our analysis to siblings born within the same post-1945 cohort. We also found support for substantial polygenic heritability of body mass index, which is consistent with a multigenic heritability. There was no significant heterogeneity between white and African-American families in support for a recessive mixed model. However, some differences in particular parameters were found, with higher gene frequency, lower polygenic heritability and a larger variance associated with the major gene model in African-Americans. CONCLUSION: Our present segregation analysis shows that the recessive pattern, whether due to single or multiple genes, cannot be explained by inter-generational differences in obesity prevalence or family correlation. There was suggestive evidence of a higher major gene frequency and larger gene effect size in African-American families.

Black People↗
PubMedDate not supplied

The meiotic segregation pattern of a reciprocal translocation t(10;12)(q26.1;p13.3) by fluorescence in situ hybridization sperm analysis.

The meiotic segregation of chromosomes 10 and 12 was analyzed in a male heterozygous for a reciprocal translocation, t(10;12)(q26.1;p13.3), using fluorescence in situ hybridization (FISH). Centromeric specific probes that detect alpha satellite sequences of chromosomes 10 and 12 were used. A total of 10,049 spermatozoa were analyzed. The frequencies of alternate/adjacent 1, adjacent 2, and 3:1 modes of segregation were: 84.25, 10.95%, and 4.42%, respectively. Diploidy was present in 0.23% of spermatozoa. Similar segregation patterns have been reported for this donor by direct karyotyping of sperm cells. FISH is a valuable technique for studying meiotic segregation patterns in that larger samples can be studied in a relatively short time. However, it does not provide information on the full chromosome complement of the spermatozoon.

Chromosomes, Human, Pair 10↗
PubMed1997

Effects of some cytoskeleton inhibitors on ooplasmic segregation in the Nereis virens egg.

The ooplasmic segregation in the Nereis virens egg starts after completion of cortical reaction. During ooplasmic segregation the radial symmetrical pattern of the oocyte transforms into polarized stratified structure with different kinds of cytoplasm regularly distributed along the animal-vegetal axis. The beginning of oocyte polarization is associated with the generation of the mitotic spindle and is sensitive to microtubule inhibitors. By analyzing the effect of colchicine, taxol, nocodazole and cytochalasin B, we show that the mechanisms of ooplasmic segregation have an integrated complex nature and include interactions of microtubules and microfilaments. The inhibition of any of these elements delays or disturbs the ooplasmic segregation and simultaneous disruption of microtubules and microfilaments functions leads to total cessation of the process.

Actins↗
PubMed1998

Revisiting occupational sex segregation in the United States, 1910-1990: results from a log-linear approach.

I reexamine trends in the strength and structure of occupational sex segregation in the United States from 1910 to 1990. Log-multiplicative models show significant change in the association between gender and occupation. Contrary to conventional characterizations, a substantial proportion of this change occurred before 1970. Likewise, a margin-free index shows more integration over the century than do conventional indices. These discrepancies arise from occupation-specific variations in the trajectory of sex segregation: Highly segregated occupations were especially likely to integrate between 1930 and 1940. I identify regions of the occupational structure and pivotal periods in which shifts in segregation occurred and compare these results with conventional historical accounts.

Censuses↗
PubMed1998

Marker segregation information in breast/ovarian cancer genetic counseling: is it still useful? Groupe Génétique et Cancer de la Fédération Nationale des Centres de Lutte Contre le Cancer.

The use of mutation screening of BRCA1 and BRCA2 genes as a genetic test is still to a certain extent limited and the oncogeneticist may want to use complementary approaches to identify at-risk individuals. In a series of 23 families with at least three breast or ovarian cancer cases, screened for mutations at BRCA1 and BRCA2 and typed for markers at both loci, we investigated the usefulness of marker segregation information at two levels: 1) to what extent can the indirect approach identify the mutation carrier status of screened cases and their first-degree relatives, and 2) in what way does it help to identify the gene implicated in a family in which neither BRCA1 nor BRCA2 mutation has been detected? Using the indirect approach, the carrier status of the screened case could be determined with quasi certainty in three families and with a high probability in eight families. This status could be inferred in unaffected first-degree relatives as almost certain in one family and as highly probable in six families. Fourteen mutations were found concurrently in our series. Among the nine mutation-negative families, we were able to conclude that a BRCA1 mutation most probably segregated in one and that a mutation other than BRCA1 and BRCA2 was probably involved in two families. Our results show that, in small families, little help is to be expected from linkage data and mutation screening is the only way of identifying the origin of a genetic predisposition in a family. Marker segregation information may be useful in some large breast/ovarian cancer families in which no BRCA1 or BRCA2 mutation has been detected.

BRCA1 Protein↗
PubMed2001

Segregation analyses of asthma and respiratory allergy: the Humboldt family study.

We performed segregation analyses of asthma and respiratory allergy based on data from 309 nuclear families comprising 1,053 individuals living in the town of Humboldt, Saskatchewan, in 1993, using the REGD program of the S.A.G.E. program package. For adults, information on asthma and history of respiratory allergy was provided by the subjects themselves, and for children by their parents. When asthma was considered as the trait in segregation analysis, models of no major effect, with or without familial effects, were rejected, but they were not rejected after adjusting for history of respiratory allergy. The major gene hypothesis was not rejected before adjusting for history of respiratory allergy. When respiratory allergy was analyzed as the trait, both major gene and multifactorial models fitted the data well, regardless of whether there was adjustment for asthma or not. Other covariates adjusted for in the segregation analyses were age, sex, number of household smokers, current smoking, number of household members, generation, and house type. The data suggest that a major gene related to respiratory allergy may explain the familial aggregation of asthma.

Adolescent↗
PubMed2004

Joubert syndrome: a haplotype segregation strategy and exclusion of the zinc finger protein of cerebellum 1 (ZIC1) gene.

Joubert syndrome (JS) is a rare autosomal recessive malformation syndrome, involving dysgenesis of the cerebellar vermis with accompanying brainstem malformations (comprising the molar tooth sign). JS is characterized by hypotonia, developmental delay, intermittent hyperpnea and apnea, and abnormal eye movements. A single locus for JS was previously identified on 9q34 in a consanguineous family of Arabian origin. However, linkage to this locus has subsequently been shown to be rare. We have ascertained 35 JS pedigrees for haplotype segregation analysis of genetic loci for genes with a putative role in cerebellar development. We examined the ZIC1 gene as a functional candidate for JS as Zic1(-/-) null mice have a phenotype reminiscent of JS. We undertook mutational analysis of ZIC1 by standard mutational analysis (dideoxy-fingerprinting (ddf)) of 47 JS probands, and fully sequenced the coding region in five of these probands. By these means, ZIC1 was excluded from playing a causal role in most cases of JS as no disease-associated mutations were identified. Further, linkage to the ZIC1 genetic locus (3q24) was excluded in 21 of 35 pedigrees by haplotype segregation analysis of closely spaced markers. The remaining 14 of 35 pedigrees were consistent with linkage. However, this number does not significantly depart from that expected by random chance (16.5) for this cohort. Therefore, this systematic approach has been validated as a means to prioritize functional candidate genes and enables us to confine mutational analysis to only those probands whose segregation is consistent with linkage to any given locus.

Abnormalities, Multiple↗
PubMed2004

A study of reciprocal translocations and inversions detected by light microscopy with special reference to origin, segregation, and recurrent abnormalities.

We analyzed 448 independently ascertained reciprocal translocations and 220 inversions referred to our diagnostic laboratory. Twenty-eight percent of the translocations and 8.5% of the inversions arose de novo, the proportion being influenced by the method of ascertainment. It was highest, 47%, among translocations ascertained through an abnormal phenotype. With the exception of the 3:1 unbalanced segregants, the remainders were equally likely to have been paternally or maternally inherited. The segregation from balanced translocation and inversion carriers showed an equal number of offspring with a normal chromosome constitution and with a balanced rearrangement. The number of unbalanced segregants among the translocations was 2.7% where the proband was balanced, and 19.2% where the proband was unbalanced. There was only a single unbalanced inversion. A search for recurring translocations showed only the well documented t(11;22) to occur with unusual frequency in our series and those of others, and we concluded that the few other translocations that were seen on more than one occasion were likely to be identical by descent (IBD). Similarly the majority of the recurring inversions, with the exception of "common variants," seemed likely to be IBD. However, eight inversions recurred in our data and in most other series and may well be genuine independent rearrangements. A search of the known olfactory receptor (OR) loci and duplicons suggested that such sequences did not form an important contribution to the breakpoints of recurring rearrangements detected by light microscopy.

Chromosome Aberrations↗
PubMed2006

Meiotic segregation analysis of reciprocal translocations both in sperms and blastomeres.

Balanced chromosomal rearrangements could lead to unbalanced segregation gametes during meiosis. In this study, sperm flourescence in situ hybridization (FISH) analysis of meiotic segregation products of four reciprocal translocations; 46,XY,t(7;10)(q21;q22), 46,XY,t(15;17)(q11;p12), 46,XY,t(6;13)(p21.1;q32), and 46,XY,t(1;13)(q24;q10) are presented. In three out of these four cases with t(15;17), t(6;13), and t(1;13) additional blastomere FISH analyses are also provided. Multi-color FISH analysis was applied using diverse probe combinations specific for translocated chromosome segments. The average frequency of sperm nuclei bearing unbalanced products for t(7;10), t(15;17), t(6;13), and t(1;13) were 48.7%, 59.5%, 60.5%, and 62.9%, respectively. Frequencies of blastomeres comprising unbalanced products in cases with t(15;17), t(6;13), and t(1;13) were 80% (12 of 15), 60% (3 of 5), and 50% (2 of 4), respectively. Chi-square test analysis showed significant differences in the meiotic segregation patterns due to the distribution and numbers of the chiasmatas that could depend on the size of the translocated segments (P < 0.001). In conclusion, FISH analysis of sperm and blastomere for reciprocal translocation carriers effectively estimates the approximate risk of unbalanced products and this result might ensure valuable genetic counseling.

Blastomeres↗
PubMed2003

Glycogen synthase kinase-3 regulates mouse oocyte homologue segregation.

Intracellular regulation of oocyte meiosis is not completely understood. However, reversible phosphorylation, which involves serine/threonine protein kinases and phosphatases (PP), is an important mediator. Glycogen synthase kinase-3 (GSK-3) is a highly conserved serine/threonine protein kinase. Currently no reports exist on presence or function of GSK-3 in mammalian oocytes. The aim of this study was to determine GSK-3 presence/absence, transcript and protein expression, intracellular protein distribution, and to investigate the functional importance of GSK-3 in mouse oocyte meiosis. Germinal vesicle-intact (GVI) oocytes contained both GSK-3 transcript and protein. Although GSK-3 beta-isoform is the only transcript identifiable in GVI oocytes, both alpha- and beta-isoforms were recognized by Western blot analysis. In growing, meiotic-incompetent oocytes GSK-3 was present, diffusely located throughout the cytoplasm and absent in the nucleus, whereas in meiotic-competent oocytes this cytoplasmic GSK-3 displays a predominant peri-oolemma staining. Treatment of mouse GVI oocytes with lithium chloride (LiCl), which inhibits both inositol monophosphatase (IMPase) and GSK-3, had no significant influence on oocyte viability, morphology, or development to metaphase II (MII). However, LiCl caused abnormal spindle formation and significantly increased incidence of abnormal homologue segregation during the first meiotic division. L690,330, which is a specific IMPase inhibitor, had no significant effect on oocyte viability, morphology, MII development, or homologue segregation. This is the first report of GSK-3 in mammalian oocytes. LiCl inhibition of mouse oocyte GSK-3 modified organization of microtubules and/or function of meiotic spindles thus compromising segregation of condensed bivalent chromosomes.

Animals↗
PubMed2006

Modeling segregation distortion for viability selection. I. Reconstruction of linkage maps with distorted markers.

Molecular markers have been widely used to map quantitative trait loci (QTL). The QTL mapping partly relies on accurate linkage maps. The non-Mendelian segregation of markers, which affects not only the estimation of genetic distance between two markers but also the order of markers on a same linkage group, is usually observed in QTL analysis. However, these distorted markers are often ignored in the real data analysis of QTL mapping so that some important information may be lost. In this paper, we developed a multipoint approach via Hidden Markov chain model to reconstruct the linkage maps given a specified gene order while simultaneously making use of distorted, dominant and missing markers in an F(2) population. The new method was compared with the methods in the MapManager and Mapmaker programs, respectively, and verified by a series of Monte Carlo simulation experiments along with a working example. Results showed that the adjusted linkage maps can be used for further QTL or segregation distortion locus (SDL) analysis unless there are strong evidences to prove that all markers show normal Mendelian segregation.

Chromosome Mapping↗
PubMed2006

Chromosome segregation in fission yeast with mutations in the tubulin folding cofactor D.

Faithful chromosome segregation requires the combined activities of the microtubule-based mitotic spindle and the multiple proteins that form mitotic kinetochores. Here, we show that the fission yeast mitotic mutant, tsm1-512, is an allele of the tubulin folding chaperone, cofactor D. Chromosome segregation in this and in an additional cofactor D mutant depends on growth conditions that are monitored specifically by the mitotic checkpoint proteins Mad1, 2, 3 and Bub3. The temperature-sensitive mutants we have used disrupt the function of cofactor D to different extents, but both strains form a mitotic spindle in which the poles separate in anaphase. However, chromosome segregation is often unequal, apparently due to a defect in kinetochore-microtubule interactions. Mutations in cofactor D render cells particularly sensitive to the expression levels of a CENP-B-like protein, Abp1p, which works as an allele-specific, high-copy suppressor of cofactor D. This and other genetic interactions between cofactor D mutants and specific kinetochore and spindle components suggest their critical role in establishing the normal kinetochore-microtubule interface.

Alleles↗
PubMed2003

Meiotic segregation of a homeologous chromosome pair.

During meiosis, the alignment of homologous chromosomes facilitates their subsequent migration away from one another to opposite spindle poles at anaphase I. Recombination is part of the mechanism by which chromosomes identify their homologous partners, and serves to link the homologs in a way that, in some organisms, has been shown to promote proper attachment to the meiotic spindle. We have built a diploid strain that contains a pair of homeologous chromosomes V': one is derived from Saccharomyces cerevisiae and one originates from S. carlsbergensis. Sequence analysis reveals that these chromosomes share 71% sequence identity. The homeologs experience high levels of meiotic double-stranded breaks. Despite their relatedness and their competence to initiate recombination, the meiotic segregation behavior of the homeologous chromosomes suggests that, in most meioses, they are partitioned by a meiotic segregation system that has been shown previously to partition non-exchange chromosomes and pairs with no homology. Though the homeologous chromosomes show a degree of meiotic segregation fidelity similar to that of other non-exchange pairs, our data provide evidence that their limited sequence homology may provide some bias in meiotic partner choice.

Base Sequence↗
PubMed2005

Unusual segregation products in sperm from a pericentric inversion 17 heterozygote.

Chromosome segregation and interchromosomal effect were studied in spermatozoa from a carrier of a pericentric chromosome 17 inversion, 46,XY,inv(17)(p13.1q25.3). Sperm chromosome segregation, lymphocytes of the inversion carrier, and cells from his offspring were analysed by multicolour fluorescence in situ hybridization. The frequency of balanced sperm was 73%. An unusual segregation of recombinants was observed, viz. deletion of the p arm (14.6%) or duplication of the p arm with the presence of one q arm (8.4%), instead of the expected recombinants, viz. duplication of one arm with deletion of the other and vice versa. These unusual recombinants were explained by the position of the 17q breakpoint, which was between the q arm telomere-associated repeats and the unique q subtelomere region. The offspring of the donor were found to have a 17p deletion including the Miller-Dieker critical region, similar to the most frequent recombinant sperm class. The disomy frequency was significantly increased for chromosome 17 compared with other autosomes, suggesting that pairing and recombination of the inversion may predispose to non-disjunction. There was no significant difference between the frequencies of aneuploidy for chromosomes 13, 21, X and Y in the chromosome inversion heterozygote compared with controls. Thus, this unique pericentric inversion of chromosome 17 produces unusual recombinant products; no evidence was apparent of an interchromosomal effect in any of the tested chromosomes.

Adult↗
PubMed2004

Anaphase spindle mechanics prevent mis-segregation of merotelically oriented chromosomes.

Merotelic kinetochore orientation is a kinetochore misattachment in which a single kinetochore is attached to microtubules from both spindle poles instead of just one. It can be favored in specific circumstances, is not detected by the mitotic checkpoint, and induces lagging chromosomes in anaphase. In mammalian cells, it occurs at high frequency in early mitosis, but few anaphase cells show lagging chromosomes. We developed live-cell imaging methods to determine whether and how the mitotic spindle prevents merotelic kinetochores from producing lagging chromosomes. We found that merotelic kinetochores entering anaphase never lost attachment to the spindle poles; they remained attached to both microtubule bundles, but this did not prevent them from segregating correctly. The two microtubule bundles usually showed different fluorescence intensities, the brighter bundle connecting the merotelic kinetochore to the correct pole. During anaphase, the dimmer bundle lengthened much more than the brighter bundle as spindle elongation occurred. This resulted in correct segregation of the merotelically oriented chromosome. We propose a model based on the ratios of microtubules to the correct versus incorrect pole for how anaphase spindle dynamics and microtubule polymerization at kinetochores prevent potential segregation errors deriving from merotelic kinetochore orientation.

Anaphase↗