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PubMed1993

RFLP analysis of chromosomal segregation in progeny from an interspecific hexaploid somatic hybrid between Solanum brevidens and Solanum tuberosum.

Segregation of restriction fragment length polymorphism (RFLP) loci was monitored to determine the degree of homeologous pairing and recombination in a hexaploid somatic hybrid, A206, the result of protoplast fusion between Solanum tuberosum (PI 203900, a tetraploid cultivated potato) and Solanum brevidens (PI 218228), a diploid, sexually incompatible, distant relative harboring several traits for disease resistance. Somatic hybrid A206 was crossed to Katahdin, a tetraploid potato cultivar, to generate a segregating population of pentaploid progeny. Although the clones of the tetraploid S. tuberosum lines PI 203900 and Katahdin were highly polymorphic, the diploid S. brevidens clone was homozygous at all but two of the tested RFLP loci. Thus, homeologous recombination could be detected only when S. tuberosum and S. brevidens chromosomes paired and the S. brevidens homologs then segregated into separate gametes. A bias toward homologous pairing was observed for all 12 chromosomes. At least four and perhaps six chromosomes participated in homologous pairing only; each of 24 progeny contained all S. brevidens-derived RFLP markers for chromosomes 4, 8, 9 and 10. The remaining six chromosomes paired with their homolog(s) about twice as often as expected if hexaploid pairings were completely random. Where detectable with RFLPs, homeologous recombination (both single and double) occurred at a frequency of 1.31 per chromosome. Cytological observations of meiosis I in the somatic hybrid indicated that homeologous pairing had occurred. Enhanced recombinational activity was observed for chromosome 2. A specific small deletion from chromosome 4 was detected in A206 and 11 other somatic hybrids out of 14 screened.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromosomes↗
PubMed1985

Meiosis in Mesostoma ehrenbergii ehrenbergii (Turbellaria, Rhabdocoela). III. Univalent chromosome segregation during the first meiotic division in spermatocytes.

At metaphase I of meiosis in spermatocytes of Mesostoma ehrenbergii ehrenbergii [2n = 10] three bivalents and four univalents form. The same two chromosome pairs always form the univalents. Analysis of metaphase I, anaphase I and metaphase II configurations in fixed testis material suggested that the distribution of the four univalents is not a random process but the correct segregation of one member of each pair to each pole is actively achieved before the end of metaphase I. In live preparations of testis material univalents were observed to move between the poles of metaphase I cells, eventually reaching the correct segregation. All cells observed to enter anaphase I had the correct segregation of univalents. It is proposed that the univalent movement during metaphase I is directed towards obtaining the correct segregation of univalents before the cells enter anaphase.

Animals↗
PubMed1996

Motors involved in spindle assembly and chromosome segregation.

During the past two years, major advances have been made in our understanding of the role of motor proteins in chromosome-microtubule interactions in the spindle. The discovery of kinesin-like proteins (KLPs) associated with chromosome arms has shed some light on the mechanism of chromosome congression and the establishment of spindle bipolarity. Recent results also indicate that kinetochore KLPs may tether the ends of growing and shrinking microtubules to kinetochores during chromosome movements. Finally, new data indicate that phosphorylation of KLPs may be one of the mechanisms by which they are targeted to specific spindle domains.

Chromosomes↗
PubMed1998

Chiasma distributions and chromosome segregation in male and female translocation heterozygous mice analysed using FISH.

Two factors postulated to influence the meiotic behaviour of reciprocal translocations were investigated. Firstly, variation in the length of translocated and non-translocated segments was studied in male mice using four different rearrangements involving chromosomes 2 and 4. Secondly, sex-related effects were analysed through comparison of the meiotic behaviour of two translocations in male and female germ cells. In the first part of the study, primary and secondary spermatocytes of male mice carrying a translocation [T(2;4)1Ca, T(2;4)13H, T(2;4)1Sn, or T(2;4)1Go] were screened. Each rearrangement had different proportions of cells with ring and chain quadrivalents at metaphase I; the T(2;4)1Sn heterozygote also had a high rate (45%) of translocation bivalents. In general, the translocations had elevated chiasma frequencies in the rearranged chromosomes compared with structurally normal chromosomes 2 and 4, although the extent of the effect varied. Each rearrangement produced a different array of segregation products at metaphase II, reflecting their contrasting frequencies of multivalent configurations at metaphase I. Comparison of chromosome behaviour at metaphase I and II suggested that certain configurations tended to adopt particular orientations. However, it was also clear that such correlations were imprecise and that other factors, possibly the exact positions of chiasmata, also played a role in multivalent orientation. Two rearrangements, T(2;4)1Go and T(7;16)67H, were analysed in female mice. The frequencies of the various multivalent types at metaphase I differed from those in male carriers of these rearrangements owing to an increased chiasma frequency in oocytes in some of the pairing segments. Not surprisingly, the segregation products seen in metaphase II cells showed some differences from the pattern recorded in male germ cells. For T(2;4)1Go, the sex-related difference in segregation patterns resulted in a diminished expectation of genetically imbalanced gametes, although this was not the case for T(7;16)67H.

Animals↗
PubMed1981

Chromosome segregation is frequently associated with the expression of recessive mutations in mouse cells.

The genes coding for adenosine kinase (ADK; ATP:adenosine 5'-phosphotransferase, EC 2.7.1.20) and esterase-10 (ES-10; carboxylesterase, carboxylic-ester hydrolase, EC 3.1.1.1) are both located on chromosome 14 in the mouse. The near-diploid mouse cell line CAK is heterozygous for two electrophoretic variants of ES-10. Recessive Adk- mutants of CAK have been isolated and analyzed for Es-10 phenotype and karyotypic abnormalities. Two classes of mutants were found with approximatley equal frequencies: those that remained heterozygous in the expression of Es-10 and those that expressed only one Es-10 allele. Of the mutants that lacked one form of ES-10, approximately half were missing most or all of one copy of chromosome 14; the other contained two copies of 14, frequently in the form of an isochromosome. There were no abnormalities of this chromosome found among the mutants that were Es-10 heterozygotes. These results suggest that the expression of an autosomal recessive mutation in near-diploid mouse cells is frequently associated with events that result in the segregation of a physically linked marker and part or all of a chromosome.

Adenosine Kinase↗
PubMed1996

Dynamic changes in nuclear architecture during mitosis: on the role of protein phosphorylation in spindle assembly and chromosome segregation.

During mitosis, the vertebrate cell nucleus undergoes profound changes in architecture. At the onset of mitosis, the nuclear envelope breaks down, the nuclear lamina is depolymerized, and interphase chromatin is condensed to chromosomes. Concomitantly, cytoplasmic microtubules are reorganized into a mitotic spindle apparatus, a highly dynamic structure required for the segregation of sister chromatids. Many of the above events are controlled by reversible phosphorylation. Hence, our laboratory is interested in characterizing the kinases involved in promoting progression through mitosis and in identifying their relevant substrates. Prominent among the kinases responsible for regulating entry into mitosis is the Cdc2 kinase, the first member of the cyclin dependent kinase (Cdk) family. Recently, we found that Cdc2 phosphorylates HsEg5, a human kinesin-related motor protein associated with centrosomes and the spindle apparatus. Our results indicate that phosphorylation regulates the association of HsEg5 with the mitotic spindle and that the function of this plus-end directed motor is essential for centrosome separation and bipolar spindle formation. Another kinase implicated in regulating progression through mitosis is Plk1 (polo-like kinase 1), the human homologue of the Drosophila gene product "polo." By antibody microinjection we have found that Plk1 is required for the functional maturation of centrosomes and hence for entry into mitosis. Furthermore, we found that microinjected anti-Plk1 antibodies caused a more severe block to cell cycle progression in diploid fibroblasts than in immortalized tumor cells. This observation hints at the existence of a checkpoint linking Cdc2 activation to the presence of functional centrosomes.

Animals↗
PubMed1987

Nonrandom chromosome arrangements in germ line nuclei of Sciara coprophila males: the basis for nonrandom chromosome segregation on the meiosis I spindle.

Meiosis I in males of the Dipteran Sciara coprophila results in the nonrandom distribution of maternally and paternally derived chromosome sets to the two division products. Based on an earlier study (Kubai, D.F. 1982. J. Cell Biol. 93:655-669), I suggested that the meiosis I spindle does not play a direct role in the nonrandom sorting of chromosomes but that, instead, haploid sets are already separated in prophase nuclei well before the onset of spindle formation. Here I report more direct evidence that this hypothesis is true; this evidence was gained from ultrastructural reconstruction analyses of the arrangement of chromosomes in germ line nuclei (prophase nuclei in spermatogonia and spermatocytes) of males heterozygous for an X-autosome chromosome translocation. Because of this translocation, the maternal and paternal chromosome sets are distinguishable, so it is possible to demonstrate that (a) the two haploid chromosome sets occupy distinct maternal and paternal nuclear compartments and that (b) nuclei are oriented so that the two haploid chromosome sets have consistent relationships to a well-defined cellular axis. The consequences of such nonrandom aspects of nuclear structure for chromosome behavior on premeiotic and meiotic spindles are discussed.

Animals↗
PubMed1995

Impaired chromosome segregation in plant anaphase after moderate hypomethylation of DNA.

10(-6) M and 10(-5) M 5-azacytidine, demethylated around 9% and 17% of the 5-methylcytosine residues found in Allium cepa L. native DNA, respectively. Both treatments stimulated RNA synthesis in the cells of root meristems. On the other hand, the 10(-5) M treatment gave rise to multiple chromosomal anomalies in mitosis before any fall in the mitotic index was detectable, but no chromosomal breaks were ever seen. Serious lesions involved in chromatids and segregation in anaphase were preferentially found after hypomethylation of DNA sequences replicated in the second half of the previous S period: (i) sister telomeres remained unresolved at the cell equator while kinetochores had reached the poles, (ii) whole unsegregated chromosomes were pulled to one of the poles by obviously disfunctional kinetochores, resulting in an unbalanced distribution of chromatids, (iii) unsegregated chromosomes in other cells remained at the spindle equator as if kinetochores were nonfunctional, while cytoplasmic division took place before their migration to the poles. Frequently, a growing cytokinetic plate randomly cut the unsegregated chromosomes, giving rise to aneuploid nuclei. These anaphase failures are a firm basis to explain why the 10(-5) M treatment selectively depressed the rate of cell proliferation in these cells in the long run. On the other hand, if hypomethylation occurred at the first half of the previous S period, enlarged chromosomal segments were evident in most metaphases, while chromosome laggards and bridges were recorded in anaphase at rather similar frequencies after the different 5-azacytidine treatments. These data were consistently obtained both in the native mononucleate cells of meristems and in one subpopulation of synchronous cells labelled as binucleate by 5 mM caffeine.

Allium↗
PubMed1989

Meiotic chromosome segregation in human t(11;22)(q23;q11) carriers: a theoretical consideration.

The t(11;22)(q23;q11) translocation is the most frequently encountered familial reciprocal translocation in humans. In the majority of reported cases ascertainment has been through the birth of a child with the chromosomal constitution 47,XX,+der(22) or 47,XY,+der(22), i.e., tertiary trisomy. Previous segregation analysis of familial cases showed a number of interesting features. Thus, euploid unbalanced genotypes resulting from adjacent segregation are absent in the progeny, and only tertiary trisomic offspring are recovered. To explain this unusual progeny output we present here a model for the meiotic behavior of this translocation in the carriers based on an analysis of cytogenetic data of progeny of carriers. This model predicts the formation of a chain trivalent with chromosome order 11-der(11)-22 during prophase I and its predominant alternate orientation at metaphase I.

Chromosomes, Human, Pair 11↗