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At least 685 records · Page 38Linked to original sources
PubMed1984

Influence of ethanol on chromosome segregation during the first and second meiotic divisions in the mouse egg.

This study was carried out to investigate the influence of ethanol on chromosome segregation during the first and second meiotic divisions. Female mice were given a single intragastric injection of a dilute solution of ethanol either just before or at various times after the HCG injection for inducing superovulation. The mice were mated, and the chromosome constitution of fertilized eggs was determined at the first cleavage mitosis. The technique employed allowed the male- and female-derived pronuclear sets to remain as two discrete groups. Exposure from 1.5 h before to 17 h after the HCG injection induced a high incidence of aneuploidy (15-25%) involving in over 90% of cases only one chromosome, so that either 19 or 21 instead of the normal complement of 20 chromosomes were present in one of the two sets (a previous study using a "marker" chromosome has demonstrated that the nondisjunction induced here invariably involves the female set). We suggest these findings draw attention to the susceptibility of chromosome segregation in female germ cells to interference by ethanol and that the mode of action is likely to be via interference with the normal functioning of the spindle apparatus. It is possible that interference with meiotic chromosome segregation by spindle-acting agents such as ethanol might account for a proportion of human spontaneous abortions with similar chromosomal defects where no other obvious cause is apparent.

Aneuploidy↗
PubMedDate not supplied

Segregation of normal and pathological human red blood cells, lymphocytes and fibroblasts by immobilized metal-ion affinity partitioning.

Immobilized metal-ion affinity partitioning (IMAP) is shown to be useful as a preliminary screening test and for the separation of different cell populations based upon recognition of the differences in the proteins on cell surfaces. The feasibility of using IMAP to segregate a spectrum of normal human cells (red blood cells, lymphocytes and fibroblasts) from their counterpart pathological cells has been demonstrated. A clear segregation between normal and sickle-cell anemia red blood cells (RBC), or malaria (Plasmodium vivax) infected RBCs was obtained. Further, the partition differences were found to depend on the nature and the concentrations of metal used. Cells from breast cancer and those from the lung adenocarcinoma showed differences in their partition pattern as compared to normal fibroblasts when PEG-IDA-M(II) was added to the phase system. Maximum differences between the three cell populations were observed in the presence of 10% PEG-IDA-Ni(II). Normal lymphocytes and Burkitt's lymphoma cells (Raji and Namalwa cell lines) were shown to partition differently in the presence of PEG-IDA-M(II) in the phase system. Normal lymphocytes could be distinguished from the Burkitt's lymphoma cell lines in all three phases (top, interface and bottom), in the presence of 10% PEG-IDA-Ni(II) in the system. These differences in the partition behavior could mainly be attributed to the density, surface exposure and micro-environment of histidine residues of cell membrane-associated proteins. These data, along with those obtained for normal and pathological human cells show that IMAP could be a simple and versatile tool for the segregation and study of cells.

Adenocarcinoma↗
PubMed2002

Evaluation of segregation patterns of 21;21 Robertsonian translocation along with sex chromosomes and interchromosomal effects in sperm nuclei of carrier by FISH technique.

Meiotic segregation patterns of carriers of Robertsonian translocations (RT) are important for assessing the risk of unbalanced forms. We investigated the ratio of sperm with t(21;21) to sperm with nullisomy for chromosome 21; the segregation of the t(21;21) along with sex chromosomes, and also interchromosomal effects on chromosome 10 by using three color fluorescence in situ hybridization (FISH) with telomere specific (Tel 21q) and centromere-specific alpha satellite probes for chromosomes X, Y, and 10. The percentage of cosegregation of t(21;21) with sex chromosomes (49.50%) and without sex chromosomes (46.98%) was not significant. There are no significant differences between the percentages of cosegregation of t(21;21) with chromosome X (23.36%) and with chromosome Y (26.16%). No evidence of an interchromosomal effect on chromosome 10 was detected, the percentage of chromosome 10 aneuploidy being similar to that in controls. In addition, the frequency of diploid sperm nuclei was not significantly higher in the carrier (0.32%) than in the controls (0.44%) (P > 0.05). The sex ratio was similar within the carrier and the controls and between the carrier and the control. Three color-FISH analysis, using different probe combinations, seems a rapid and accurate tool for direct analysis of meiotic segregation product.

Adult↗
PubMed1992

Evidence for differential maturation of reciprocal sperm segregants in the murine Rb(6.16) translocation heterozygote.

The fertilizing ability of unaged sperm and those aged experimentally in the cauda by surgically ligating the corpus epididymis in males carrying the Rb(6.16) translocation was studied. Chromosomally normal females were inseminated with unaged sperm delivered by males mating at 3-day intervals, and aged sperm were studied after matings on 6-14 postoperative days. The sperm chromosome complement was analyzed in first-cleavage metaphase zygotes after sequential G- and C-banding of the chromosomes. Of 283 metaphasic zygotes in the control group, 183 (or 64.7%) were analyzed and showed a ratio of 2.7:1 for chromosomally normal and balanced segregants of the translocation, deviating significantly (P less than 0.001) from the expected 1:1. The ratio of X- to Y-bearing sperm also deviated from expected (P less than 0.01) mostly due to a significant deficiency (P less than 0.05) of balanced sperm that were X-bearing. Fertilized oocytes were recovered from matings of 10 males on days 6-8 postoperatively, and, of 139 metaphasic one-cell zygotes, 101 (or 72.3%) were analyzed. These showed a Mendelian ratio of 1:1 for normal and balanced segregants. The sex ratio in the aged group (57Y:41X) also showed no deviation from 1:1. The results, which reveal significant physiological distortions for both the segregation and the sex ratios in males heterozygous for the Rb(6.16) translocation, suggest that differential maturation of the translocation-bearing sperm and the chromosomally normal reciprocal exists. The findings further support the concept that sperm chromosomal complement affects their maturation and function, and that factors on chromosome 6 and the X or Y chromosome additively affect sperm function.

Animals↗
PubMed2002

Hybrid monte carlo method for simulation of two-component aerosol coagulation and phase segregation.

The paper presents the development of a hybrid Monte Carlo (MC) method for the simulation of the simultaneous coagulation and phase segregation of an immiscible two-component binary aerosol. The model is intended to qualitatively model our prior studies of the synthesis of mixed metal oxides for which phase-segregated domains have been observed in molten nanodroplets. In our previous works (J. Aerosol Sci.32, 1479 (2001); Chem. Eng. Sci.56, 5763 (2001); submitted for publication) we developed sectional and monodisperse models where the internal state of the aerosol particles was described. These methods have certain limitations and it is difficult to include additional physical effects into the framework. Our new approach combines both constant volume and constant number Monte Carlo methods. Similar to our previous models, we assume that the phase segregation is kinetically controlled. The MC approach allows us to compute the mean number of enclosures (minor phase) per droplet, average enclosure volume, and the width of the enclosure size distribution. The results show that asymptotic behavior of enclosure distribution exists that is independent of initial conditions, which is very close to the continuum self-preserving distribution. Temperature is a key parameter because it allows for a significant change in the internal transport rate within each droplet. In particular, increasing the temperature significantly enhances the Brownian coagulation rate and lowers the number of enclosures per droplet. As a result, the MC results indicate that the growth of the minor phase can be moderated quite dramatically by small changes in system temperature. These results serve to illustrate the utility of this synthesis approach to the controlled growth of nanoparticles through the use of a majority matrix to slow down the encounter frequency of the minor phase and therefore its particle size.

Journal Article↗
PubMed1995

Mechanism of post-segregational killing: secondary structure analysis of the entire Hok mRNA from plasmid R1 suggests a fold-back structure that prevents translation and antisense RNA binding.

The hok/sok system of plasmid R1 mediates plasmid stabilization by killing of plasmid-free cells. The Hok mRNA is very stable and can be translated into Hok killer protein. Translation of the Hok mRNA is inhibited by the small unstable Sok antisense RNA. Translation of hok is coupled to an overlapping reading frame termed mok. Translation of mok is tightly regulated by Sok RNA, and Sok RNA thus regulates hok translation indirectly through mok. The rapid decay of Sok RNA explains the onset of Hok synthesis in newborn plasmid-free segregants. However, a second control level is superimposed on this simple induction scheme, since the full-length Hok mRNA was found to be translationally inactive whereas a 3'-end truncated version of it was active. We have therefore previously suggested, that the 3'-terminal region of the full-length Hok mRNA encodes an element which prevents its translation. This element was termed fbi (fold-back inhibition). Here we describe the in vitro secondary structure of the entire Hok mRNA. Our results suggest a closed structure in which the 3'-end of the full-length Hok mRNA folds back onto the translational initiation region of mok. This structure explains why full-length Hok mRNA is translationally silent. The proposed structure was further supported by results obtained using mutations in the 3'-end fbi element. These "structure closing" mutations affected the structure much further upstream in the mok translational initiation region and concomitantly prevented antisense RNA binding to the same region of the mRNA. These results lend further support to the induction model that explains onset of Hok mRNA translation in plasmid-free segregants. The most important regulatory element in this model is the FBI structure formed between the 3'-end and the mok translational initiation region. This structure renders Hok mRNA translationally inactive and prevents antisense RNA binding, thus allowing the accumulation of a pool of mRNA which, by slow 3'-end processing, is activated in plasmid-free segregants, eventually leading to the elimination of these cells.

Bacterial Proteins↗
PubMed1998

Use of differential display in conjunction with bulked segregants to target specific genomic loci.

Differential display has proven to be a very successful technique for isolating differentially expressed transcripts. We sought to expand the capabilities of the technique by attempting to isolate cDNAs from specific genomic loci. Two loci of interest to us are the S locus and the MOD locus, both involved in the self-incompatibility phenomenon of Brassica. The S locus is a complex locus for which molecular markers have previously been isolated, and the MOD locus is a single-gene locus for which no markers are available. We used plant material from F2 populations that segregate for two allelic variants of each locus to create two bulks or pools of plants for each differential display screen. Pooling F2 individuals effectively homogenizes background polymorphisms found in the parent plants. RNA was prepared from each bulk and differential display was performed using a kit from GenHunter Corporation (Nashville, TN). One cDNA that segregated completely with the target locus was isolated from each screen. Multiple cDNAs that were linked to each locus were also identified. We have demonstrated that differential display, when used in conjunction with bulked segregants, is a very powerful technique for isolating cDNAs from genomic loci of interest.

Brassica↗
PubMed1995

Use of continuous culture for the selection of plasmids with improved segregational stability.

In this report a method that enables the selection of stable plasmid variants and the isolation of DNA sequences that improve plasmid maintenance is described. The method is based on the principle that in populations of cells carrying derivatives of a plasmid that differ only in the level of segregational stability, when grown in a chemostat under conditions with selective pressure on the plasmid, cells that carry more stable plasmid variants will be enriched. We developed the system for Lactococcus lactis using segregationally unstable derivatives of the gram-positive theta plasmid pAM beta 1 as selection vectors. The results showed that the method is suitable for the enrichment, and subsequent purification, of three classes of plasmids with improved maintenance properties. The first class involved mutations in the pAM beta 1-derived selection plasmid. These mutations resulted in increased copy numbers, thereby rendering the plasmid segregationally more stable. The other two classes were based on the insertion of additional, stability promoting, sequences in the selection plasmids. We showed that these sequences can constitute either replication functions derived from another plasmid or functions directly involved in plasmid maintenance. The site-specific resolution function of pAM beta 1 was used as an example of the latter functions. We anticipate that the method described should have general applicability for the development of stable host-vector systems in bacteria.

Bacteriological Techniques↗
PubMed1995

Mechanisms of chromosome segregation in metazoan cells.

Despite over 100 year of research, the mechanisms that cells use to ensure the proper segregation of chromosomes during mitosis are still surprisingly obscure. However, recent high resolution video light microscopic studies of dividing cells are telling us new and important information about chromosome behavior. Molecular genetics is enabling us to build a more complete list of the components involved in chromosome segregation. And in vitro assays for chromosome segregation are providing information about the signals that control the equipartitioning of sister chromatids during cell division.

Animals↗
PubMed1995

Intracellular heteroplasmy for disease-associated point mutations in mtDNA: implications for disease expression and evidence for mitotic segregation of heteroplasmic units of mtDNA.

Studies in vitro have shown that a respiratory-deficient phenotype is expressed by cells when the proportion of mtDNA with a disease-associated mutation exceeds a threshold level, but analysis of tissues from patients with mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) have failed to show a consistent relationship between the degree of heteroplasmy and biochemical expression of the defect. One possible explanation for this phenomenon is that there is variation of heteroplasmy between individual cells that is not adequately reflected by the mean heteroplasmy for a tissue. We have confirmed this by study of fibroblast clones from subjects heteroplasmic for the MELAS 3243 (A-->G) mtDNA mutation. Similar observations were made with fibroblast clones derived from two subjects heteroplasmic for the 11778 (G-->A) mtDNA mutation of Leber's hereditary optic neuropathy. For the MELAS 3243 mutation, the distribution of mutant mtDNA between different cells was not randomly distributed about the mean, suggesting that selection against cells with high proportions of mutant mtDNA had occurred. To explore the way in which heteroplasmic mtDNA segregates in mitosis we followed the distribution of heteroplasmy between clones over approximately 15 generations. There was either no change or a decrease in the variance of intercellular heteroplasmy for the MELAS 3243 mutation, which is most consistent with segregation of heteroplasmic units of multiple mtDNA molecules in mitosis. After mitochondria from one of the MELAS 3243 fibroblast cultures were transferred to a mitochondrial DNA-free (rho0) cell line derived from osteosarcoma cells by cytoplast fusion, the mean level and intercellular distribution of heteroplasmy was unchanged. We interpret this as evidence that somatic segregation (rather than nuclear background or cell differentiation state) is the primary determinant of the level of heteroplasmy.

Adolescent↗
PubMed1976

Pattern of somatic segregation of the cytoplasmic drug-resistance factors in yeast.

The pattern of somatic segregation of the cytoplasmic factors confering resistances to chloramphenicol, erythromycin and oligomyin in S. cerevisiae was studied. The fractions of the zygotes heterozygous for the chloramphenicol-resistance factor and for the erythromycin-resistance factor decreased exponentially with generation number of zygotes. The rate of the segregation was highest for the chloramphenicol-resistance factor and lowest for the oligomycin-resistance factor. The segregation rate as well as the transmission polarity of the chloramphenicol-resistance factor varied with different carbon sources with which the parental haploids were grown prior to mating.

Chloramphenicol↗
PubMed1983

Chromosome segregation into the spermatozoa of two men heterozygous for different reciprocal translocations.

Sperm chromosomes from two human males, each heterozygous for a different reciprocal translocation, were examined. Chromosomally normal sperm were found in equal numbers to those carrying the translocation in the balanced form, in both males. Alternate segregation was more common than adjacent segregation in both translocations. Male W. G. had a greater proportion of sperm containing chromosome abnormalities unrelated to the translocation than did J.S., the second made studied. J.S. however, had a greater frequency of chromosomally unbalanced sperm. The great majority of unbalanced sperm in both males was due to adjacent I segregation.

Adult↗
PubMed1990

Analysis of meiotic segregation in a man heterozygous for a 13;15 Robertsonian translocation and a review of the literature.

Meiotic segregation was studied in a male heterozygous for a 13;15 Robertsonian translocation using in vitro sperm penetration of hamster eggs. Sixty-seven sperm chromosome complements were obtained and R-banded. Alternate segregation produced equal numbers of normal (31) and balanced (29) gametes, as was theoretically expected. Incidence of unbalanced complements was 10.4%, and the frequency of abnormalities unrelated to the translocation was 7.4%. This study confirms the predominance of alternate meiotic segregation in Robertsonian translocation carriers. Four sperm studies of Robertsonian translocation have been previously reported. A review of the combined results points out the low incidence of imbalance in the sperm of Robertsonian translocation carrier and the lack of evidence for an interchromosomal effect.

Adult↗
PubMed1990

The Escherichia coli minB mutation resembles gyrB in defective nucleoid segregation and decreased negative supercoiling of plasmids.

Nucleoid segregation in the Escherichia coli minB mutant and in cells that over-produce minB gene products appeared defective as measured from fluorescence micrographs. Electrophoretic resolution of topoisomers of plasmid isolates from the minB strain revealed a decreased level of negative supercoiling; in addition, multimerization was observed. Over-production of the minB gene product also resulted in a decreased level of negative supercoiling. This phenotype is typical of the gyrB(ts) mutant, which is known to be affected in chromosome decatenation and supercoiling. We propose that the minB mutation and over-production of the minB gene products cause a defect in nucleoid segregation, which may be related to the decrease in negative supercoiling. As in the gyrB(ts) mutant, retardation of nucleoid segregation is proposed to inhibit constriction initiation in the cell centre and to give rise to nucleoid-free cell poles. As a consequence, these cells divide between nucleoid and cell pole, resulting in minicell and (sometimes) in anucleate cell formation.

Bacterial Proteins↗
PubMed1994

Segregation analysis and RFLP mapping of the R1 and R3 alleles conferring race-specific resistance to Phytophthora infestans in progeny of dihaploid potato parents.

Phytophthora infestans (Mont.) de Bary is the most important fungal pathogen of the potato (Solanum tuberosum). The introduction of major genes for resistance from the wild species S. demissum into potato cultivars is the earliest example of breeding for resistance using wild germplasm in this crop. Eleven resistance alleles (R genes) are known, differing in the recognition of corresponding avirulence alleles of the fungus. The number of R loci, their positions on the genetic map and the allelic relationships between different R variants are not known, except that the R1 locus has been mapped to potato chromosome V. The objective of this work was the further genetic analysis of different R alleles in potato. Tetraploid potato cultivars carrying R alleles were reduced to the diploid level by inducing haploid parthenogenetic development of 2n female gametes. Of the 157 isolated primary dihaploids, 7 set seeds and carried the resistance alleles R1, R3 and R10 either individually or in combinations. Independent segregation of the dominant R1 and R3 alleles was demonstrated in two F1 populations of crosses among a dihaploid clone carrying R1 plus R3 and susceptible pollinators. Distorted segregation in favour of susceptibility was found for the R3 allele in 15 of 18 F1 populations analysed, whereas the R1 allele segregated with a 1:1 ratio as expected in five F1 populations. The mode of inheritance of the R10 allele could not be deduced as only very few F1 hybrids bearing R10 were obtained. Linkage analysis in two F1 populations between R1, R3 and RFLP markers of known position on the potato RFLP maps confirmed the position of the R1 locus on chromosome V and localized the second locus, R3, to a distal position on chromosome XI.

Alleles↗
PubMed1995

The effects of a ring chromosome on the meiotic segregation of other chromosomes in Saccharomyces cerevisiae.

Meiotic chromosome segregation must occur with high fidelity in order to prevent the generation of aneuploid cells. We have previously described the identification and genetic characterization of a yeast mutant with defects in meiotic sister-chromatid segregation. We attributed the phenotype in this mutant to a dominant allele, which we referred to as SID1-1. These mutants appeared to exhibit high levels of non-disjunction and precocious separation of sister-chromatids of chromosome III, as well as precocious separation of sister chromatids of chromosome VIII and a univalent artificial chromosome. We show here that the unusual meiotic behavior of chromosome III in these strains is due to the presence of a ring III chromosome, rather than a mutant gene. Additional experiments demonstrate that a ring III/rod III pair alters the meiotic segregation of a univalent artificial chromosome.

Chromosomes, Artificial, Yeast↗
PubMed1985

Chromosome segregation and spindle structure in crane fly spermatocytes following Colcemid treatment.

Chromosome segregation in primary spermatocytes of the crane fly Nephrotoma suturalis was studied after exposure to Colcemid at doses that did not completely inhibit spindle formation. Colcemid was added either to the medium in which larvae were cultured or to Tricine buffer in which isolated testes were incubated. Patterns of chromosome segregation were analyzed in fixed, Feulgen-stained smears of testes from Colcemid-treated larvae and in living cell preparations. Anomalies observed during the first meiotic division at higher than normal frequencies in Colcemid-treated spermatocytes included anaphase lagging of autosomes, chromosomal strands, tripolar and tetrapolar divisions, and unequal distribution of chromosomes to secondary cells. Following those doses of Colcemid that induced the above anomalies, the length of the birefringent spindle in primary spermatocytes was shorter than normal. This effect on spindle length also was apparent in Giemsa-stained preparations of fixed cells, in which the two centrosomes at the spindle poles were differentiated from the rest of the cytoplasm. The results indicate a correlation between the inhibition of spindle formation and the induction of anomalous patterns of chromosome segregation.

Animals↗
PubMed1976

Chromosome constitution of in vitro segregated haploid and diploid cells of the mouse.

The composition in segregated haploid sets of paternal and maternal chromosomes has been studied in order to verify whether their composition is uniparental of mixed, fixed or variable. Primary cultures where prepared using kidneys from hybrids of strains of Mus musculus in which the parental chromosomes are distinguishable; the maternal set consists of 20 teleocentric chromosomes, the paternal set of 9 metacentric chromosomes, derived by Robertsonian fusion and 2 telocentrics. Applying Seabright's banding technique, an analysis of segregated haploid and diploid cells, which have originated spontaneously through polyploidisation-segregation processes was carried out. It was concluded that the haploid sets have a variable composition of paternal and maternal chromosomes.

Animals↗