Synaptonemal Complex Central Region Proteins Promote Localization of Pro-crossover Factors to Recombination Events DuringCaenorhabditis elegansMeiosis

Abstract

Errors during meiosis are the leading cause of birth defects and miscarriages in humans. Thus, the coordinated control of meiotic events is critical for the faithful inheritance of the genome with each generation...

Quantitative Cytogenetics Reveals Molecular Stoichiometry and Longitudinal Organization of Meiotic Chromosome Axes and Loops

“…Based on our data and findings from previously-published literature (Severson et al, 2009;Severson and Meyer, 2014;Cahoon et al, 2019;Kim et al, 2014;Crawley et al, 2016), we propose the following model for the assembly and organization of meiotic When REC-8 is globally or locally absent, axis-promoting cohesin complexes (COH-3/4 in C. elegans or RAD21L in mouse) and HORMADs assemble functional chromosome axes and loops on single DNA molecules (FIG2C; Agostinho et al, 2016;Cahoon et al, 2019). Thus, we propose that on wild-type meiotic prophase chromosomes, COH-3/4containing cohesin complexes also bind to individual chromatids between REC-8 mediated cohesion sites.…”

“…Based on these analyses, we conclude that most of the individual REC-8 foci in the fully spread preparations each represents a single cohesin complex. We note that REC-8-containing cohesin complexes appear to be the only cohesins that connect sister chromatids during meiotic prophase in a classical cohesive manner, as COH-3/4 complexes not only bind to chromosomes after replication, but bind to individual chromatids and are insufficient to mediate sister chromatid cohesion in the absence of REC-8 (Severson and Meyer 2014;Crawley et al, 2016;Cahoon et al 2019;FIG2C).…”

“…Third, analysis of spread nuclei from rec-8 mutants provides additional evidence for a functional distinction between REC-8 and COH-3/4 cohesin complexes, by demonstrating a capacity for COH-3/4 cohesin complexes to interact with individual chromatids. In rec-8 mutants, when only COH-3/4 cohesin complexes are present on chromatin during meiotic prophase, SCs frequently form and crossover recombination apparently occurs between sister chromatids (rather than between homologs), suggesting that axes assemble along individual chromatids in this context (Crawley et al, 2016;Cahoon et al, 2019). However, not all chromosomes engage in synapsis in rec-8 mutants (Cahoon et al, 2019), and we were able to trace the paths of both synapsed and unsynapsed axes in late prophase nuclei of rec-8 mutants (FIG2C).…”

“…In rec-8 mutants, when only COH-3/4 cohesin complexes are present on chromatin during meiotic prophase, SCs frequently form and crossover recombination apparently occurs between sister chromatids (rather than between homologs), suggesting that axes assemble along individual chromatids in this context (Crawley et al, 2016;Cahoon et al, 2019). However, not all chromosomes engage in synapsis in rec-8 mutants (Cahoon et al, 2019), and we were able to trace the paths of both synapsed and unsynapsed axes in late prophase nuclei of rec-8 mutants (FIG2C). This analysis confirmed the interpretation that continuous chromosome axes (containing HTP-3 and COH-3/4) do indeed form along individual chromatids in the rec-8 mutant (FIG2C and FIG2S1C).…”

Chromosome-Level Assembly of theCaenorhabditis remaneiGenome Reveals Conserved Patterns of Nematode Genome Organization

“…Pairing of chromosomes during meiosis in C. elegans is initiated from specific regions ("pairing centers") located on the ends of homologous chromosomes (MacQueen et al 2005;Tsai and McKee 2011), followed by chromosome synapsis via assembly of the synaptonemal complex along coupled chromosomes (MacQueen et al 2002;Rog and Dernburg 2013). Crossovers in C. elegans can be formed only between properly synapsed regions (Lui and Colaiácovo 2013;Cahoon et al 2019). Taken together, these molecular mechanisms permit meiotic recombination only between homologous regions linked in cis to the pairing centers, which presumably reduces the number of interchromosomal rearrangements, thereby resulting in the evolutionary stability of the nematode karyotype (Rog and Dernburg 2013).…”