Abstract
Nuclear receptor HR97 is considered as a non-insect arthropod-specific receptor, but its roles in decapod reproduction remain poorly understood. Here, we identified and characterized an HR97 ortholog from the swimming crab Portunus trituberculatus (PtHR97) and verified its placement within the NR1L nuclear receptor family by phylogenetic analysis. PtHR97 encodes a canonical nuclear receptor with a conserved DNA-binding domain (DBD) and ligand-binding domain (LBD). Quantitative PCR revealed predominant PtHR97 expression in the ovary and stage-dependent changes during ovarian development. Using an ovarian explant culture system, we found that arachidonic acid (AA) consistently suppressed PtHR97 transcript levels, while methyl farnesoate (MF) and pyriproxyfen (P) had no significant effect, indicating a potential inhibitory role for AA in PtHR97 expression. RNA interference of HR97 caused significant changes in ovarian development, including reduced GSI, smaller oocytes, and uneven eosinophilic granule distribution. Transcriptomic profiling of HR97-silenced ovaries indicated that the major responses involved genes associated with substrate transport/exchange, cell boundary-related signaling and transduction, and disturbed nuclear transcriptional regulation. Short-term in vivo perturbations (HR97 RNAi and AA treatment) further supported these expression changes and revealed that AA- and HR97 RNAi-elicited transcriptional responses only partially overlapped. Taken together, these results suggest that HR97 contributes to ovarian development, potentially through broad transcriptional responses related to transport, signaling, and gene regulation. Although AA may suppress HR97 expression, HR97 does not fully explain AA-mediated regulation of ovarian development.