Rad21l1 cohesin subunit is dispensable for spermatogenesis but not oogenesis in zebrafish

During meiosis I, ring-shaped cohesin complexes play important roles in
aiding the proper segregation of homologous chromosomes. RAD21L is a
meiosis-specific vertebrate cohesin that is required for spermatogenesis
in mice but is dispensable for oogenesis in young animals. The role of
this cohesin in other vertebrate models has not been explored. Here, we
tested if the zebrafish homolog Rad21l1 is required for meiotic chromosome
dynamics during spermatogenesis and oogenesis. We found that Rad21l1
localizes to unsynapsed chromosome axes. It is also found between the axes
of the mature tripartite synaptonemal complex (SC) in both sexes. We
knocked out rad21l1 and found that nearly
all rad21l1-/- mutants develop as fertile males,
suggesting that the mutation causes a defect in juvenile oogenesis, since
insufficient oocyte production triggers female to male sex reversal in
zebrafish. Sex reversal was partially suppressed by mutation of the
checkpoint gene tp53, suggesting that
the rad21l1 mutation activates Tp53-mediated apoptosis
or arrest in females. This response, however, is not linked to a defect in
repairing Spo11-induced double-strand breaks since deletion
of spo11 does not suppress the sex reversal phenotype.
Compared to tp53 single mutant
controls, rad21l1-/- tp53-/- double mutant
females produce poor quality eggs that often die or develop into malformed
embryos. Overall, these results indicate that the absence
of rad21l1-/- females is due to a checkpoint-mediated
response and highlight a role for a meiotic-specific cohesin subunit in
oogenesis but not spermatogenesis.