Journal
GENETICS
Volume 207, Issue 1, Pages 103-114Publisher
GENETICS SOCIETY AMERICA
DOI: 10.1534/genetics.117.204172
Keywords
meiosis; homolog pairing; synaptonemal complex; pairing centers; Caenorhabditis elegans
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Funding
- National Institutes of Health Office of Research Infrastructure Programs [P40 OD-010440]
- American Cancer Society Postdoctoral Fellowship
- Beckman Senior Research Fellowship
- American Cancer Society Research Professor Award [RP-15-209-01-DDC]
- National Institutes of Health [R01 GM-53804]
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Segregation of homologous chromosomes during meiosis depends on their ability to reorganize within the nucleus, discriminate among potential partners, and stabilize pairwise associations through assembly of the synaptonemal complex (SC). Here we report a high-resolution time-course analysis of these key early events during Caenorhabditis elegans meiosis. Labeled nucleotides are incorporated specifically into the X chromosomes during the last 2 hr of S phase, a property we exploit to identify a highly synchronous cohort of nuclei. By tracking X-labeled nuclei through early meiotic prophase, we define the sequence and duration of chromosome movement, nuclear reorganization, pairing at pairing centers (PCs), and SC assembly. Appearance of ZYG-12 foci (marking attachment of PCs to the nuclear envelope) and onset of active mobilization occur within an hour after S-phase completion. Movement occurs for nearly 2 hr before stable pairing is observed at PCs, and autosome movement continues for similar to 4 hr thereafter. Chromosomes are tightly clustered during a 2-3 hr postpairing window, during which the bulk of SC assembly occurs; however, initiation of SC assembly can precede evident chromosome clustering. SC assembly on autosomes begins immediately after PC pairing is detected and is completed within similar to 3.5 hr. For the X chromosomes, PC pairing is contemporaneous with autosomal pairing, but autosomes complete synapsis earlier (on average) than X chromosomes, implying that X chromosomes have a delay in onset and/or a slower rate of SC assembly. Additional evidence suggests that transient association among chromosomes sharing the same PC protein may contribute to partner discrimination.
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