title: Interplay between synaptonemal complex, homologous recombination, and centromeres during mammalian meiosis.
abstract: The intimate synapsis of homologous chromosome pairs (homologs) by synaptonemal complexes (SCs) is an essential feature of meiosis. In many organisms, synapsis and homologous recombination are interdependent: recombination promotes SC formation and SCs are required for crossing-over. Moreover, several studies indicate that initiation of SC assembly occurs at sites where crossovers will subsequently form. However, recent analyses in budding yeast and fruit fly imply a special role for centromeres in the initiation of SC formation. In addition, in budding yeast, persistent SC-dependent centromere-association facilitates the disjunction of chromosomes that have failed to become connected by crossovers. Here, we examine the interplay between SCs, recombination, and centromeres in a mammal. In mouse spermatocytes, centromeres do not serve as SC initiation sites and are invariably the last regions to synapse. However, centromeres are refractory to de-synapsis during diplonema and remain associated by short SC fragments. Since SC-dependent centromere association is lost before diakinesis, a direct role in homolog segregation seems unlikely. However, post-SC disassembly, we find evidence of inter-centromeric connections that could play a more direct role in promoting homolog biorientation and disjunction. A second class of persistent SC fragments is shown to be crossover-dependent. Super-resolution structured-illumination microscopy (SIM) reveals that these structures initially connect separate homolog axes and progressively diminish as chiasmata form. Thus, DNA crossing-over (which occurs during pachynema) and axis remodeling appear to be temporally distinct aspects of chiasma formation. SIM analysis of the synapsis and crossover-defective mutant Sycp1⁻/⁻ implies that SCs prevent unregulated fusion of homolog axes. We propose that SC fragments retained during diplonema stabilize nascent bivalents and help orchestrate local chromosome reorganization that promotes centromere and chiasma function.
authors: Howard Hughes Medical Institute and Departments of Microbiology, Molecular and Cellular Biology, and Cell Biology and Human Anatomy, University of California Davis, Davis, California, United States of America.
authors: Huanyu
authors: H
authors: Qiao
authors: Jefferson K
authors: JK
authors: Chen
authors: April
authors: A
authors: Reynolds
authors: Christer
authors: C
authors: Höög
authors: Michael
authors: M
authors: Paddy
authors: Neil
authors: N
authors: Hunter
mesh_terms: D000818:Animals; D027682:Cation Transport Proteins / Q000235:genetics; D002503:Centromere / Q000235:genetics* / Q000648:ultrastructure; D023902:Chromosome Pairing / Q000235:genetics; D002875:Chromosomes / Q000235:genetics / Q000648:ultrastructure; D004268:DNA-Binding Proteins; D004706:Endodeoxyribonucleases / Q000235:genetics; D059765:Homologous Recombination / Q000235:genetics*; D008297:Male; D008540:Meiosis / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D009687:Nuclear Proteins / Q000235:genetics; D013090:Spermatocytes / Q000166:cytology; D013573:Synaptonemal Complex / Q000235:genetics* / Q000648:ultrastructure; D000099257:Meiotic Recombination Protein SPO11
chemical_list: D027682:Cation Transport Proteins; D004268:DNA-Binding Proteins; D004706:Endodeoxyribonucleases; D009687:Nuclear Proteins; D000099257:Meiotic Recombination Protein SPO11; C498426:Slc39a3 protein, mouse; C489754:Sycp1 protein, mouse