DAZ-family proteins play important roles in meiosis and gametogenesis. They are RNP-type RNA-binding proteins that carry two well-conserved RRMs (RNA Recognition Motifs) in their N-terminus, followed by a highly diverged C-terminal tract. The C. elegans homolog of DAZ,
daz-1, is necessary for oogenesis but not for spermatogenesis. DAZ-1 protein is mainly localized in the mitotic and early meiotic regions in hermaphrodite and male gonads. We have previously reported identification of the
daz-1 homologs in C. briggsae and C. remanei. Comparison of the deduced amino acid sequences of the nematode DAZ homologs showed that the N-terminal RRM regions were highly conserved among the three species, whereas the C-terminal region was diverged. Ce-DAZ-1 (499 a.a.) and Cr-DAZ-1 (452 a.a.) had long unique C-terminal regions (349 a.a. and 297 a.a., respectively), which were missing in most DAZ-family proteins, but their amino acid sequences were not highly similar to each other. Cb-DAZ-1 was the smallest among the three (224 a.a.), with only 61 amino acid residues in the C-terminal region. When expressed from
Ce-daz-1 promoter,
Cr-daz-1 rescued the sterility of the
daz-1 mutant to some extent, whereas
Cb-daz-1 did not.
Ce-daz-1 deleted of the C-terminal region did not restore fertility to the
daz-1 mutant. These observations suggest that the long C-terminal region seen in
Ce-daz-1 and
Cr-daz-1 may play some crucial role in C. elegans. Unlike C. elegans, RNAi of
Cb-daz-1 in C. briggsae caused a Mog phenotype in F1 hermaphrodites, implicating a role for the gene in spermatogenesis-to-oogenesis switching. In mature P0 hermaphrodites,
Cb-daz-1 RNAi "switched off" oogenesis that had already started, and induced re-initiation of spermatogenesis. Based on the results of
Cb-daz-1 RNAi, we examined whether C. elegans
daz-1 plays any role in spermatogenesis-to-oogenesis switching. We found that the
daz-1 mutation lowered the restriction temperature of the temperature-sensitive Mog mutant
fem-3(
q20). Moreover,
daz-1 RNAi performed on
fem-3(
q20) mature adult hermaphrodites caused re-initiation of spermatogenesis. These results suggest that C. elegans
daz-1 is likely to play a role in germline sex switching.