FIGURE 3.

The C. elegans germ line presents a spatial temporal organization of events during meiotic prophase I. (A) At the distal proliferative zone, germline stem cells mitotically divide to produce cells that will advance down the gonad and enter meiosis. Chromosome pairing and DSBs induction by SPO-11 occur in leptotene/zygotene (transition zone), which is characterized by the presence of clustered chromatin on one side of the nuclei. DSBs are processed and bound by RAD-51 for homologous recombinational repair, which are visible as RAD-51 foci by immunostaining starting in leptotene through pachytene. The synaptonemal complex (SC) is fully assembled between the homologs in pachytene and strictly one crossover forms between each chromosome pair in late pachytene. Upon crossover formation, the SC disassembles and homologs undergo remodeling and compaction to reveal six bivalents at diakinesis stage. (B) Cartoon of chromosome structure observed in diakinesis nuclei in WT (6 bivalents), brc-1 (6 bivalents), syp-2 (12 univalents), brc1; syp-2 (> 12 univalents/DNA fragments) (Adamo et al., 2008), brc-2 (aggregation), lig-4 (RNAi) brc-2 (12 univalents with some DNA fragments) and lig-4 (RNAi); rad-51 (aggregation) (Martin et al., 2005) mutants.