CDC25 phosphatase promotes cell cycles by removing an inhibitory phosphate from CDK/Cyclin complex. In C. elegans, there are four
cdc-25 family members,
cdc-25.1,
cdc-25.2,
cdc-25.3 and
cdc-25.4. CDC-25.2 regulates oocyte maturation and its mutation causes endomitotic oocyte (Emo) phenotype, resulting in sterility in hermaphrodites. Interestingly,
cdc-25.2 RNAi caused Emo in both germline- and soma-specific RNAi strains. These results suggest that the Emo in
cdc-25.2 mutants is caused by defects not only in germ cells but also in somatic gonads. We found that
cdc-25.2 was highly expressed in the spermatheca and
cdc-25.2 mutants showed abnormal spermathecal development. To investigate regulation of
cdc-25.2 expression in the spermatheca, we examined the regulatory elements of
cdc-25.2. Both promoter and intron1 of
cdc-25.2 were required for expression of a
cdc-25.2 transgene in spermathecal precursor cells at the L1 stage, however promoter or intron1 was required at the L3 stage or at the L4 stage, respectively. Transcriptional factors of
cdc-25.2 in spermatheca were searched using databases and two transcriptional activators, FKH-6 and NHR-6 whose multiple binding sites are present in both promoter and intron1 of
cdc-25.2 were identified. RNAi depletion of
fkh-6 or
nhr-6 significantly suppressed expression of
cdc-25.2 in the spermatheca cells from the L1 stage or L3 stage, respectively, and showed severe Emo phenotype. These results indicate that FKH-6 and NHR-6 activate
cdc-25.2 expression stage-specifically. Currently, binding sites of NHR-6 in the promoter or/and intron1 of
cdc-25.2 is mutated using CRISPR-Cas9 to analyze roles of NHR-6 in the later stages of spermathecal development. Taken together, we suggest that stage-specific activation of
cdc-25.2 by FKH-6 and NHR-6 using promoter or/and intron1 is essential for the proper spermathecal development in C. elegans. This study was supported by the National Research Foundation of Korea grant funded by the Korean Ministry of Science and ICT (NRF-2018R1A2B6007915).