Identification and involvement of DAX1 gene in spermatogenesis of boring giant clam Tridacna crocea

DAX1 (dosage-sensitive sex reversal, adrenal hypoplasia congenital critical region on X chromosome gene 1), a key sex determinant in various species, plays a vital role in gonad differentiation and development and controls spermatogenesis. However, the identity and function of DAX1 are still unclear in bivalves. In the present study, we identified a DAX1 (designed as Tc-DAX1) gene from the boring giant clam Tridacna crocea, a tropical marine bivalve. The full length of Tc-DAX1 was 1877 bp, encoding 462 amino acids, with a Molecular weight of 51.81 kDa and a theoretical Isoelectric point of 5.87 (pI). Multiple sequence alignments and phylogenetic analysis indicated a putative ligand binding domain (LBD) conserved regions clustered with molluscans DAX1 homologs. The tissue distributions in different reproductive stages revealed a dimorphic pattern, with the highest expression trend in the male reproductive stage, indicating its role in spermatogenesis. The DAX1 expression data from embryonic stages shows its highest expression profile (P < 0.05) in the zygote stage, followed by decreasing trends in the larvae stages (P > 0.05). The localization of DAX1 transcripts has also been confirmed by whole mount in situ hybridization, showing high positive signals in the fertilized egg, 2, and 4-cell stage, and gastrula. Moreover, RNAi knockdown of the Tc-DAX1 transcripts shows a significantly lower expression profile in the ds-DAX1 group compared to the ds-EGFP group. Subsequent histological analysis of gonads revealed that spermatogenesis was affected in a ds-DAX1 group compared to the ds-EGFP group. Collectively, all these results indicate that Tc-DAX1 is involved in the spermatogenesis and early embryonic development of T. crocea, providing valuable information for the breeding and aquaculture of giant clams.