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Canadian Journal of Genetics and... Dec 1983The schematic representation of RHG-banded chromosomes (R-banding was produced by heat denaturation followed by Giemsa staining (RHG) in the 850-band range per haploid...
The schematic representation of RHG-banded chromosomes (R-banding was produced by heat denaturation followed by Giemsa staining (RHG) in the 850-band range per haploid set, was prepared showing the relative position, the specific size, and the characteristic staining intensity for each band. To this idiogram was adapted the new International Standard Cytogenetic Nomenclature. Our aim was to produce a realistic idiogram which could help in the preparation of R-banded prophase karyotypes and in the localization of chromosomal rearrangements. A comparative analysis of bands at prophase and metaphase revealed certain aspects of the dynamics involved in chromosome condensation and in R-band organization. The effect of chromosome elongation on the appearance of R-bands within heterochromatic regions has also been discussed.
Topics: Adult; Chromosome Banding; Chromosomes, Human; Female; Humans; Male; Metaphase; Middle Aged; Prophase; Reference Values; Staining and Labeling
PubMed: 6200193
DOI: 10.1139/g83-095 -
Molecular Reproduction and Development Sep 2005Nucleolar organization by autosomal bivalents occurs during male meiotic prophase in mammalian species. During late leptotene-early zygotene stages, several autosomal... (Review)
Review
Nucleolar organization by autosomal bivalents occurs during male meiotic prophase in mammalian species. During late leptotene-early zygotene stages, several autosomal bivalents are engaged in ribosomal RNA synthesis. At pachytene stage, nucleolar masses detach from the sites of primary autosomal origin, relocate close to the XY chromosomal pair, and nucleolar components become segregated. In early pachytene, an extensive synaptonemal complex at the pseudoautosomal region, links X and Y chromosomes in close juxtaposition along most of the length of the Y chromosome, except for a terminal region of the Y that diverges from the pairing region. As meiotic prophase advances, X and Y chromosomes progressively desynapse and, at diplotene, the XY pair is associated end-to-end. Xmr (Xlr-related, meiosis regulated) is a protein component of the nucleolus associated to the XY pair and of the asynapsed portions of the X and Y axial cores. Xmr, like SCP3, is a component of the lateral element of the synaptonemal complex. Both share structural homology in their C-terminal region. This region contains several putative coiled-coil domains known to mediate heterodimeric protein-protein interactions and to provide binding sites to regulatory proteins. Like Xmr, the tumor repressor protein BRCA1 is present along the unsynapsed cores of the XY bivalent. Both Xmr and BRCA1 have been implicated in a mechanism leading to chromatin condensation and transcription inactivation of the XY bivalent. The BRCA1-ATR kinase complex, as recent research suggests, triggers the phosphorylation of histone H2AX, which predominates in the condensed chromatin of the XY chromosomal pair. Xmr is not present in the XY bivalent when the expression of histone H2AX is deficient. The role of Xmr in chromatin condensation of the XY bivalent has not been determined. The partial structural homology of SCP3 and Xmr, their distribution along the unsynapsed axial cores of the X and Y chromosomes, and the presence of Xmr in the XY pair-associated nucleolus raises the possibility that Xmr, and other proteins including protein kinases, may be recruited to the nucleolus to perform functions related to chromosomal synapsis, chromatin condensation and recombination processes, as well as cell cycle progression.
Topics: Animals; Cell Nucleolus; Humans; Male; Pachytene Stage; Synaptonemal Complex; X Chromosome; Y Chromosome
PubMed: 15915516
DOI: 10.1002/mrd.20334 -
Science (New York, N.Y.) Aug 2003The separation of homologous chromosomes during meiosis in eukaryotes is the physical basis of Mendelian inheritance. The core of the meiotic process is a specialized... (Review)
Review
The separation of homologous chromosomes during meiosis in eukaryotes is the physical basis of Mendelian inheritance. The core of the meiotic process is a specialized nuclear division (meiosis I) in which homologs pair with each other, recombine, and then segregate from each other. The processes of chromosome alignment and pairing allow for homolog recognition. Reciprocal meiotic recombination ensures meiotic chromosome segregation by converting sister chromatid cohesion into mechanisms that hold homologous chromosomes together. Finally, the ability of sister kinetochores to orient to a single pole at metaphase I allows the separation of homologs to two different daughter cells. Failures to properly accomplish this elegant chromosome dance result in aneuploidy, a major cause of miscarriage and birth defects in human beings.
Topics: Animals; Chromosome Pairing; Chromosome Segregation; Chromosomes; DNA; Humans; Meiosis; Synaptonemal Complex
PubMed: 12907787
DOI: 10.1126/science.1086605 -
Journal of Cell Science Mar 2010The kinesin-8 proteins are a family of microtubule-depolymerising motor molecules, which, despite their highly conserved roles in chromosome alignment and spindle...
The kinesin-8 proteins are a family of microtubule-depolymerising motor molecules, which, despite their highly conserved roles in chromosome alignment and spindle dynamics, remain poorly characterised. Here, we report that the Drosophila kinesin-8 protein, Klp67A, exists in two spatially and functionally separable metaphase pools: at kinetochores and along the spindle. Fixed and live-cell analyses of different Klp67A recombinant variants indicate that this kinesin-8 first collects at kinetochores during prophase and, by metaphase, localises to the kinetochore outerplate. Although the catalytic motor activity of Klp67A is required for efficient kinetochore recruitment at all times, microtubules are entirely dispensable for this process. The tail of Klp67A does not play a role in kinetochore accumulation, but is both necessary and sufficient for spindle association. Using functional assays, we reveal that chromosome position and spindle length are determined by the microtubule-depolymerising motor activity of Klp67A exclusively when located at kinetochores, but not along the spindle. These data reveal that, unlike other metazoan kinesin-8 proteins, Klp67A binds the nascent prophase and mature metaphase kinetochore. From this location, Klp67A uses its motor activity to ensure chromosome alignment and proper spindle length.
Topics: Animals; Animals, Genetically Modified; Blotting, Western; Cells, Cultured; Drosophila; Drosophila Proteins; Fluorescent Antibody Technique; Kinetochores; Microtubule-Associated Proteins; Microtubules; Polymerase Chain Reaction; Prophase; Protein Binding; RNA Interference; Spindle Apparatus
PubMed: 20144994
DOI: 10.1242/jcs.055905 -
Genes & Development Dec 2020Proper segregation during meiosis requires that homologs be connected by the combination of crossovers and sister chromatid cohesion. To generate crossovers, numerous... (Review)
Review
Proper segregation during meiosis requires that homologs be connected by the combination of crossovers and sister chromatid cohesion. To generate crossovers, numerous double-strand breaks (DSBs) are introduced throughout the genome by the conserved Spo11 endonuclease. DSB formation and its repair are then highly regulated to ensure that homologous chromosomes contain at least one crossover and no DSBs remain prior to meiosis I segregation. The synaptonemal complex (SC) is a meiosis-specific structure formed between homologous chromosomes during prophase that promotes DSB formation and biases repair of DSBs to homologs over sister chromatids. Synapsis occurs when a particular recombination pathway is successful in establishing stable interhomolog connections. In this issue of , Mu and colleagues (pp. 1605-1618) show that SC formation between individual chromosomes provides the feedback to down-regulate Spo11 activity, thereby revealing an additional function for the SC.
Topics: Chromatids; DNA Breaks, Double-Stranded; Homologous Recombination; Meiosis; Synaptonemal Complex
PubMed: 33262143
DOI: 10.1101/gad.345488.120 -
Biology of Reproduction Dec 2003When the Y chromosome of a Mus musculus domesticus male mouse (caught in Tirano, Italy) is placed on a C57BL/6J genetic background, approximately half of the XY...
When the Y chromosome of a Mus musculus domesticus male mouse (caught in Tirano, Italy) is placed on a C57BL/6J genetic background, approximately half of the XY (B6.YTIR) progeny develop into normal-appearing but infertile females. We have previously reported that the primary cause of infertility can be attributed to their oocytes. To identify the primary defect in the XY oocyte, we examined the onset and progress of meiotic prophase in the B6.YTIR fetal ovary. Using bromo-deoxyuridine incorporation and culture, we determined that the germ cells began to enter meiosis at the developmental ages and in numbers comparable to those in the control XX ovary. Furthermore, the meiotic prophase appeared to progress normally until the late zygotene stage. However, the oocytes that entered meiosis early in the XY ovary failed to complete the meiotic prophase. On the other hand, a considerable number of oocytes entered meiosis at late developmental stages and completed the meiotic prophase in the XY ovary. We propose that the timing of entry into meiosis and the XY chromosomal composition influence the survival of oocytes during meiotic prophase in the fetal ovary.
Topics: Animals; Cells, Cultured; Disorders of Sex Development; Female; Infertility, Female; Meiosis; Mice; Mice, Mutant Strains; Oocytes; Ovary; Prophase; X Chromosome; Y Chromosome
PubMed: 12904311
DOI: 10.1095/biolreprod.103.017541 -
Biology of the Cell Nov 1998Oogonia undergo numerous mitotic cell cycles before completing the last DNA replication and entering the meiotic prophase I. After chromosome pairing and chromatid... (Review)
Review
Oogonia undergo numerous mitotic cell cycles before completing the last DNA replication and entering the meiotic prophase I. After chromosome pairing and chromatid exchanges between paired chromosomes, the oocyte I remains arrested at the diplotene stage of the first meiotic prophase. Oocyte growth then occurs independently of cell division; indeed, during this growth period, oocytes (4n DNA) are prevented from completing the meiotic divisions. How is the prophase arrest regulated? One of the players of the prophase block is the high level of intracellular cAMP, maintained by an active adenylate cyclase. By using lethal toxin from Clostridium sordellii (LT), a glucosyltransferase that glucosylates and inactivates small G proteins of the Ras subfamily, we have shown that inhibition of either Ras or Rap or both proteins is sufficient to release the prophase block of Xenopus oocytes in a cAMP-dependent manner. The implications of Ras family proteins as new players involved in the prophase arrest of Xenopus oocytes will be discussed here.
Topics: Animals; Calcium-Calmodulin-Dependent Protein Kinases; Oocytes; Prophase; Xenopus; ras Proteins
PubMed: 10069002
DOI: No ID Found -
PLoS Genetics Nov 2020In the two cell divisions of meiosis, diploid genomes are reduced into complementary haploid sets through the discrete, two-step removal of chromosome cohesion, a task...
In the two cell divisions of meiosis, diploid genomes are reduced into complementary haploid sets through the discrete, two-step removal of chromosome cohesion, a task carried out in most eukaryotes by protecting cohesion at the centromere until the second division. In eukaryotes without defined centromeres, however, alternative strategies have been innovated. The best-understood of these is found in the nematode Caenorhabditis elegans: after the single off-center crossover divides the chromosome into two segments, or arms, several chromosome-associated proteins or post-translational modifications become specifically partitioned to either the shorter or longer arm, where they promote the correct timing of cohesion loss through as-yet unknown mechanisms. Here, we investigate the meiotic axis HORMA-domain protein HIM-3 and show that it becomes phosphorylated at its C-terminus, within the conserved "closure motif" region bound by the related HORMA-domain proteins HTP-1 and HTP-2. Binding of HTP-2 is abrogated by phosphorylation of the closure motif in in vitro assays, strongly suggesting that in vivo phosphorylation of HIM-3 likely modulates the hierarchical structure of the chromosome axis. Phosphorylation of HIM-3 only occurs on synapsed chromosomes, and similarly to other previously-described phosphorylated proteins of the synaptonemal complex, becomes restricted to the short arm after designation of crossover sites. Regulation of HIM-3 phosphorylation status is required for timely disassembly of synaptonemal complex central elements from the long arm, and is also required for proper timing of HTP-1 and HTP-2 dissociation from the short arm. Phosphorylation of HIM-3 thus plays a role in establishing the identity of short and long arms, thereby contributing to the robustness of the two-step chromosome segregation.
Topics: Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Cell Cycle Proteins; Chromosomal Proteins, Non-Histone; Chromosome Pairing; Chromosome Segregation; Chromosomes; Meiosis; Phosphorylation; Prophase; Protein Domains; Synaptonemal Complex
PubMed: 33175901
DOI: 10.1371/journal.pgen.1008968 -
Journal of Cell Science Sep 2019High-fidelity chromosome segregation relies on proper microtubule regulation. Kinesin-8 has been shown to destabilise microtubules to reduce metaphase spindle length and...
High-fidelity chromosome segregation relies on proper microtubule regulation. Kinesin-8 has been shown to destabilise microtubules to reduce metaphase spindle length and chromosome movements in multiple species. XMAP215/chTOG polymerases catalyse microtubule growth for spindle assembly, elongation and kinetochore-microtubule attachment. Understanding of their biochemical activity has advanced, but little work directly addresses the functionality and interplay of these conserved factors. We utilised the synthetic lethality of fission yeast kinesin-8 (Klp5-Klp6) and XMAP215/chTOG (Dis1) to study their individual and overlapping roles. We found that the non-motor kinesin-8 tailbox is essential for mitotic function; mutation compromises plus-end-directed processivity. Klp5-Klp6 induces catastrophes to control microtubule length and, surprisingly, Dis1 collaborates with kinesin-8 to slow spindle elongation. Together, they enforce a maximum spindle length for a viable metaphase-anaphase transition and limit elongation during anaphase A to prevent lagging chromatids. Our work provides mechanistic insight into how kinesin-8 negatively regulates microtubules and how this functionally overlaps with Dis1 and highlights the importance of spindle length control in mitosis.
Topics: Anaphase; Chromosome Segregation; Kinesins; Kinetochores; Microscopy, Fluorescence; Microtubule-Associated Proteins; Microtubules; Prophase; Schizosaccharomyces; Schizosaccharomyces pombe Proteins; Spindle Apparatus
PubMed: 31427431
DOI: 10.1242/jcs.232306 -
Developmental Biology Mar 2004Maintenance of meiotic prophase arrest in fully grown vertebrate oocytes depends on an elevated level of cAMP in the oocyte. To investigate how the cAMP level is...
Maintenance of meiotic prophase arrest in fully grown vertebrate oocytes depends on an elevated level of cAMP in the oocyte. To investigate how the cAMP level is regulated, we examined whether the activity of an oocyte G protein of the family that stimulates adenylyl cyclase, Gs, is required to maintain meiotic arrest. Microinjection of a dominant negative form of Gs into Xenopus and mouse oocytes, or microinjection of an antibody that inhibits the Gs G protein into zebrafish oocytes, caused meiosis to resume. Together with previous studies, these results support the conclusion that Gs-regulated generation of cAMP by the oocyte is a common mechanism for maintaining meiotic prophase arrest in vertebrate oocytes.
Topics: Animals; Blotting, Western; GTP-Binding Protein alpha Subunits, Gs; Meiosis; Mice; Oocytes; Prophase; Xenopus laevis; Zebrafish
PubMed: 14975713
DOI: 10.1016/j.ydbio.2003.11.011