A Caenorhabditis elegans cohesion protein with functions in meiotic chromosome pairing and disjunction

We have studied four Caenorhabditis elegans homologs of the Rad21/Scc1/Rec8 sister-chromatid cohesion protein family. Based on the RNAi phenotype and protein localization, it is concluded that one of them, W02A2.6p, is the li kely worm ortholog of yeast Rec8p. The depletion of C. elegans W02A2.6p (ca lled REC-8) by RNAi, induced univalent formation and splitting of chromosom es into sister chromatids at diakinesis. Chromosome synapsis at pachytene w as defective, but primary homology recognition seemed unaffected, as a clos er-than-random association of homologous fluorescence in situ hybridization (FISH) signals at leptotene/zygotene was observed. Depletion of REC-8 also induced chromosome fragmentation at diakinesis. We interpret these fragmen ts as products of unrepaired meiotic double-stranded DNA breaks (DSBs), bec ause fragmentation was suppressed in a spo-11 background. Thus, REC-8 seems to be required for successful repair of DSBs. The occurrence of DSBs in RE C-8-depleted meiocytes suggests that DSB formation does not depend on homol ogous synapsis. Anti-REC-8 immunostaining decorated synaptonemal complexes (SCs) at pachytene and chromosomal axes in bivalents and univalents at diak inesis. Between metaphase I and metaphase II, REC-8 is partially lost from the chromosomes. The partial loss of REC-8 from chromosomes between metapha se I and metaphase II suggests that worm REC-8 might function similarly to yeast Rec8p. The loss of yeast Rec8p from chromosome arms at meiosis I and centromeres at meiosis II coordinates the disjunction of homologs and siste r chromatids at the two meiotic divisions.