Gonadal Development-Related Genes and a Male-Specific Genetic Marker Identified in the Endangered Sichuan Taimen (Hucho bleekeri).

Sex determination and differentiation represent fundamental topics in reproductive biology. Sichuan taimen (Hucho bleekeri), a first-class national protected fish species in China, lacks obvious secondary sexual characteristics, making it challenging to distinguish sex without resorting to invasive methods such as dissection. This limitation presents a significant obstacle to both artificial breeding and conservation efforts for the species. Herein, we performed transcriptome and proteome sequencing to identify sex-biased genes of H. bleekeri. A total of 25 258 significantly differentially expressed genes (DEGs) were identified in gonadal tissues, including 15 071 up-regulated male-biased DEGs. Proteomics analysis identified 2937 differentially expressed proteins (DEPs). Integrated analysis identified several key DEGs, including sdY, CYP11A1, 3β-HSD1, CYP17A1, CYP11B, CYP19A1A, 17β-HSD1, and 17β-HSD8, in which CYP11A1, 3β-HSD1, CYP17A1, and CYP11B exhibited high expression in the testis. Furthermore, the cDNA sequence of the sdY gene was obtained, and in situ hybridization revealed that sdY is exclusively expressed in the Sertoli cells of the testis. In addition, one pair of sdY primers was designed to screen sex-linked markers, and the results confirmed that sdY can serve as a sex-specific marker in H. bleekeri. The present study would provide a foundation for future research on genes involved in sex determination, differentiation, and artificial breeding in H. bleekeri.