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Proceedings of the National Academy of... Oct 2022The synaptonemal complex (SC) is a proteinaceous scaffold that is assembled between paired homologous chromosomes during the onset of meiosis. Timely expression of SC...
The synaptonemal complex (SC) is a proteinaceous scaffold that is assembled between paired homologous chromosomes during the onset of meiosis. Timely expression of SC coding genes is essential for SC assembly and successful meiosis. However, SC components have an intrinsic tendency to self-organize into abnormal repetitive structures, which are not assembled between the paired homologs and whose formation is potentially deleterious for meiosis and gametogenesis. This creates an interesting conundrum, where SC genes need to be robustly expressed during meiosis, but their expression must be carefully regulated to prevent the formation of anomalous SC structures. In this manuscript, we show that the Polycomb group protein Sfmbt, the ortholog of human MBTD1 and L3MBTL2, is required to avoid excessive expression of SC genes during prophase I. Although SC assembly is normal after Sfmbt depletion, SC disassembly is abnormal with the formation of multiple synaptonemal complexes (polycomplexes) within the oocyte. Overexpression of the SC gene and depletion of other Polycomb group proteins are similarly associated with polycomplex formation during SC disassembly. These polycomplexes are highly dynamic and have a well-defined periodic structure. Further confirming the importance of Sfmbt, germ line depletion of this protein is associated with significant metaphase I defects and a reduction in female fertility. Since transcription of SC genes mostly occurs during early prophase I, our results suggest a role of Sfmbt and other Polycomb group proteins in downregulating the expression of these and other early prophase I genes during later stages of meiosis.
Topics: Chromosomal Proteins, Non-Histone; Chromosome Pairing; Female; Humans; Meiosis; Meiotic Prophase I; Polycomb-Group Proteins; Synaptonemal Complex
PubMed: 36215502
DOI: 10.1073/pnas.2204701119 -
Nature Communications Oct 2021During meiosis, chromosomes exhibit dramatic changes in morphology and intranuclear positioning. How these changes influence homolog pairing, alignment, and...
During meiosis, chromosomes exhibit dramatic changes in morphology and intranuclear positioning. How these changes influence homolog pairing, alignment, and recombination remain elusive. Using Hi-C, we systematically mapped 3D genome architecture throughout all meiotic prophase substages during mouse spermatogenesis. Our data uncover two major chromosome organizational features varying along the chromosome axis during early meiotic prophase, when homolog alignment occurs. First, transcriptionally active and inactive genomic regions form alternating domains consisting of shorter and longer chromatin loops, respectively. Second, the force-transmitting LINC complex promotes the alignment of ends of different chromosomes over a range of up to 20% of chromosome length. Both features correlate with the pattern of homolog interactions and the distribution of recombination events. Collectively, our data reveal the influences of transcription and force on meiotic chromosome structure and suggest chromosome organization may provide an infrastructure for the modulation of meiotic recombination in higher eukaryotes.
Topics: Animals; Chromosome Pairing; Flow Cytometry; Homologous Recombination; Humans; In Situ Hybridization, Fluorescence; Male; Meiosis; Mice; Mice, Inbred C57BL; RNA-Seq; Spermatocytes
PubMed: 34625553
DOI: 10.1038/s41467-021-26033-0 -
International Journal of Molecular... Feb 2021Cyclin-dependent kinases (CDKs) are crucial regulators of the eukaryotic cell cycle. The critical role of CDK2 in the progression of meiosis was demonstrated in a single...
Cyclin-dependent kinases (CDKs) are crucial regulators of the eukaryotic cell cycle. The critical role of CDK2 in the progression of meiosis was demonstrated in a single mammalian species, the mouse. We used immunocytochemistry to study the localization of CDK2 during meiosis in seven rodent species that possess hetero- and homomorphic male sex chromosomes. To compare the distribution of CDK2 in XY and XX male sex chromosomes, we performed multi-round immunostaining of a number of marker proteins in meiotic chromosomes of the rat and subterranean mole voles. Antibodies to the following proteins were used: RAD51, a member of the double-stranded DNA break repair machinery; MLH1, a component of the DNA mismatch repair system; and SUN1, which is involved in the connection between the meiotic telomeres and nuclear envelope, alongside the synaptic protein SYCP3 and kinetochore marker CREST. Using an enhanced protocol, we were able to assess the distribution of as many as four separate proteins in the same meiotic cell. We showed that during prophase I, CDK2 localizes to telomeric and interstitial regions of autosomes in all species investigated (rat, vole, hamster, subterranean mole voles, and mole rats). In sex bivalents following synaptic specificity, the CDK2 signals were distributed in three different modes. In the XY bivalent in the rat and mole rat, we detected numerous CDK2 signals in asynaptic regions and a single CDK2 focus on synaptic segments, similar to the mouse sex chromosomes. In the mole voles, which have unique XX sex chromosomes in males, CDK2 signals were nevertheless distributed similarly to the rat XY sex chromosomes. In the vole, sex chromosomes did not synapse, but demonstrated CDK2 signals of varying intensity, similar to the rat X and Y chromosomes. In female mole voles, the XX bivalent had CDK2 pattern similar to autosomes of all species. In the hamster, CDK2 signals were revealed in telomeric regions in the short synaptic segment of the sex bivalent. We found that CDK2 signals colocalize with SUN1 and MLH1 signals in meiotic chromosomes in rats and mole voles, similar to the mouse. The difference in CDK2 manifestation at the prophase I sex chromosomes can be considered an example of the rapid chromosome evolution in mammals.
Topics: Animals; Cell Cycle Proteins; Cyclin-Dependent Kinase 2; Female; Male; Mammals; Meiotic Prophase I; Models, Biological; Pachytene Stage; Rats; Sex Chromosomes; Spermatocytes
PubMed: 33671248
DOI: 10.3390/ijms22041969 -
Nature Structural & Molecular Biology Mar 2019In meiotic prophase, chromosomes are organized into compacted loop arrays to promote homolog pairing and recombination. Here, we probe the architecture of the mouse...
In meiotic prophase, chromosomes are organized into compacted loop arrays to promote homolog pairing and recombination. Here, we probe the architecture of the mouse spermatocyte genome in early and late meiotic prophase using chromosome conformation capture (Hi-C). Our data support the established loop array model of meiotic chromosomes, and infer loops averaging 0.8-1.0 megabase pairs (Mb) in early prophase and extending to 1.5-2.0 Mb in late prophase as chromosomes compact and homologs undergo synapsis. Topologically associating domains (TADs) are lost in meiotic prophase, suggesting that assembly of the meiotic chromosome axis alters the activity of chromosome-associated cohesin complexes. While TADs are lost, physically separated A and B compartments are maintained in meiotic prophase. Moreover, meiotic DNA breaks and interhomolog crossovers preferentially form in the gene-dense A compartment, revealing a role for chromatin organization in meiotic recombination. Finally, direct detection of interhomolog contacts genome-wide reveals the structural basis for homolog alignment and juxtaposition by the synaptonemal complex.
Topics: Animals; Chromatin; Chromosome Pairing; Chromosomes; DNA Breaks; Genome; Homologous Recombination; Male; Meiotic Prophase I; Mice; Mice, Inbred C57BL; Spermatocytes; Spermatogenesis; Synaptonemal Complex
PubMed: 30778236
DOI: 10.1038/s41594-019-0187-0 -
PLoS Genetics Jul 2023The successful delivery of genetic material to gametes requires tightly regulated interactions between the parental chromosomes. Central to this regulation is a... (Review)
Review
The successful delivery of genetic material to gametes requires tightly regulated interactions between the parental chromosomes. Central to this regulation is a conserved chromosomal interface called the synaptonemal complex (SC), which brings the parental chromosomes in close proximity along their length. While many of its components are known, the interfaces that mediate the assembly of the SC remain a mystery. Here, we survey findings from different model systems while focusing on insight gained in the nematode C. elegans. We synthesize our current understanding of the structure, dynamics, and biophysical properties of the SC and propose mechanisms for SC assembly.
Topics: Animals; Synaptonemal Complex; Caenorhabditis elegans; Meiosis; Chromosome Pairing; Caenorhabditis elegans Proteins
PubMed: 37471284
DOI: 10.1371/journal.pgen.1010822 -
Current Biology : CB Nov 2020Checkpoint cascades link cell cycle progression with essential chromosomal processes. During meiotic prophase, recombination and chromosome synapsis are monitored by...
Checkpoint cascades link cell cycle progression with essential chromosomal processes. During meiotic prophase, recombination and chromosome synapsis are monitored by what are considered distinct checkpoints. In budding yeast, cells that lack the AAA+ ATPase Pch2 show an impaired cell cycle arrest in response to synapsis defects. However, unperturbed pch2Δ cells are delayed in meiotic prophase, suggesting paradoxical roles for Pch2 in cell cycle progression. Here, we provide insight into the checkpoint roles of Pch2 and its connection to Hop1, a HORMA domain-containing client protein. Contrary to current understanding, we find that Pch2 (together with Hop1) is crucial for checkpoint function in response to both recombination and synapsis defects, thus revealing a shared meiotic checkpoint cascade. Meiotic checkpoint responses are transduced by DNA break-dependent phosphorylation of Hop1. Based on our data and on the described effect of Pch2 on HORMA topology, we propose that Pch2 promotes checkpoint proficiency by catalyzing the availability of signaling-competent Hop1. Conversely, we demonstrate that Pch2 can act as a checkpoint silencer, also in the face of persistent DNA repair defects. We establish a framework in which Pch2 and Hop1 form a homeostatic module that governs general meiotic checkpoint function. We show that this module can-depending on the cellular context-fuel or extinguish meiotic checkpoint function, which explains the contradictory roles of Pch2 in cell cycle control. Within the meiotic prophase checkpoint, the Pch2-Hop1 module thus operates analogous to the Pch2/TRIP13-Mad2 module in the spindle assembly checkpoint that monitors chromosome segregation.
Topics: Chromosome Segregation; DNA-Binding Proteins; Feedback, Physiological; M Phase Cell Cycle Checkpoints; Nuclear Proteins; Phosphorylation; Prophase; Protein Multimerization; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Spindle Apparatus; Synaptonemal Complex
PubMed: 32916108
DOI: 10.1016/j.cub.2020.08.064 -
Developmental Cell Apr 2002During mitosis, in most eukaryotes, cohesin is removed from chromosomes in two steps. A paper in the March issue of Molecular Cell identifies Polo-like kinase as a key... (Review)
Review
During mitosis, in most eukaryotes, cohesin is removed from chromosomes in two steps. A paper in the March issue of Molecular Cell identifies Polo-like kinase as a key regulator for the first step that releases much of cohesin during prophase.
Topics: Animals; Cell Cycle Proteins; Chromosome Segregation; Drosophila Proteins; Prophase; Protein Serine-Threonine Kinases; Xenopus Proteins
PubMed: 11970886
DOI: 10.1016/s1534-5807(02)00155-7 -
Development (Cambridge, England) Apr 2018To prevent chromosomal aberrations being transmitted to the offspring, strict meiotic checkpoints are in place to remove aberrant spermatocytes. However, in about 1% of...
To prevent chromosomal aberrations being transmitted to the offspring, strict meiotic checkpoints are in place to remove aberrant spermatocytes. However, in about 1% of males these checkpoints cause complete meiotic arrest leading to azoospermia and subsequent infertility. Here, we unravel two clearly distinct meiotic arrest mechanisms that occur during prophase of human male meiosis. Type I arrested spermatocytes display severe asynapsis of the homologous chromosomes, disturbed XY-body formation and increased expression of the Y chromosome-encoded gene and seem to activate a DNA damage pathway leading to induction of p63, possibly causing spermatocyte apoptosis. Type II arrested spermatocytes display normal chromosome synapsis, normal XY-body morphology and meiotic crossover formation but have a lowered expression of several cell cycle regulating genes and fail to silence the X chromosome-encoded gene Discovery and understanding of these meiotic arrest mechanisms increases our knowledge of how genomic stability is guarded during human germ cell development.
Topics: Apoptosis; Azoospermia; Cell Cycle Checkpoints; DNA Damage; DNA Repair; Gene Expression Profiling; Humans; Kruppel-Like Transcription Factors; Male; Meiosis; Prophase; Spermatocytes; Spermatogenesis; Transcription Factors; Tumor Suppressor Proteins
PubMed: 29540502
DOI: 10.1242/dev.160614 -
Fungal Genetics and Biology : FG & B Oct 2011Mitosis in Aspergillus nidulans is very rapid, requiring less than 5 min at 37 °C in germlings (Bergen and Morris, 1983). In this time the cytoplasmic microtubules...
Mitosis in Aspergillus nidulans is very rapid, requiring less than 5 min at 37 °C in germlings (Bergen and Morris, 1983). In this time the cytoplasmic microtubules (MTs) must disassemble, the mitotic spindle assemble, function and disassemble, and cytoplasmic MTs reassemble. It follows that cytoplasmic MTs must be extremely dynamic in this period and we were interested, in particular, in examining the processes of MT disassembly in prophase and reassembly in anaphase and telophase. We observed a diploid strain that expressed GFP-α-tubulin. We used a spinning disk confocal microscope that allowed rapid image capture, which proved necessary because microtubule dynamics were extremely rapid. We found, for the first time, that microtubule severing occurs in prophase in a filamentous fungus and that catastrophe rather than nucleation limits astral microtubule growth.
Topics: Anaphase; Aspergillus nidulans; Diploidy; Haploidy; Microtubules; Mitosis; Prophase; Spindle Apparatus; Telophase
PubMed: 21807107
DOI: 10.1016/j.fgb.2011.07.003 -
Cell Reports Jan 2024Dynamic chromosome remodeling and nuclear compartmentalization take place during mammalian meiotic prophase I. We report here that the crucial roles of male...
Dynamic chromosome remodeling and nuclear compartmentalization take place during mammalian meiotic prophase I. We report here that the crucial roles of male pachynema-specific protein (MAPS) in pachynema progression might be mediated by its liquid-liquid phase separation in vitro and in cellulo. MAPS forms distinguishable liquid phases, and deletion or mutations of its N-terminal amino acids (aa) 2-9 disrupt its secondary structure and charge properties, impeding phase separation. Maps pachytene spermatocytes exhibit defects in nucleus compartmentalization, including defects in forming sex bodies, altered nucleosome composition, and disordered chromatin accessibility. Maps male mice expressing MAPS protein lacking aa 2-9 phenocopy Maps mice. Moreover, a frameshift mutation in C3orf62, the human counterpart of Maps, is correlated with nonobstructive azoospermia in a patient exhibiting pachynema arrest in spermatocyte development. Hence, the phase separation property of MAPS seems essential for pachynema progression in mouse and human spermatocytes.
Topics: Humans; Male; Mice; Animals; Chromatin; Meiosis; Pachytene Stage; Phase Separation; Meiotic Prophase I; Spermatocytes; Mammals
PubMed: 38175751
DOI: 10.1016/j.celrep.2023.113651