The expression and function of gpr54a and gpr54b in allotriploid crucian carp and diploid red crucian carp (Carassius auratus red var.)

The kisspeptin receptor (GPR54), a member of the G-protein-coupled receptors, plays a central role in regulating reproduction. However, research on GPR54 in allotriploid fish remains limited. In this study, we reported the full-length cDNAs, tissue expression, and localization of gpr54a and gpr54b in allotriploid crucian carp (ACC) and diploid red crucian carp ( Carassius auratus red var., RCC). The full-length cDNAs of gpr54a in ACC and RCC were 2224 bp and 2218 bp, respectively. The full-length cDNAs of gpr54b in ACC and RCC were 1413 bp and 1182 bp, respectively. qRT-PCR revealed that ACC gpr54a and RCC gpr54a were highly expressed in the brain but had lower expression in peripheral tissues. Unlike gpr54a , ACC gpr54b and RCC gpr54b were highly expressed in the brain, liver, and muscle. During the breeding season, the expression of gpr54a in ACC was significantly lower than in RCC, but gpr54b had significantly higher expression in ACC than in RCC in the HPG axis. This finding suggested that gpr54a might promote ovarian development, while gpr54b might inhibit ovarian development. During the breeding season, ISH indicated abnormal ovarian development in ACC and found signals of gpr54a and gpr54b in several regions of the brain, pituitary, and ovary of ACC and RCC. These regions of the brain, pituitary, and ovary are associated with the secretion of several hormones related to reproductive regulation. Hence, we hypothesized that the lower expression of gpr54a and higher expression of gpr54b in ACC might be involved in sterility by regulating the secretion of reproductive hormones. This study suggested that gpr54a and gpr54b might function oppositely in regulating reproduction. In conclusion, these findings will aid in further investigating the functions of GPR54 and provide a theoretical basis for studying ACC sterility.