Abstract:In this study, the full length cDNA sequence of Rachycentron canadum dnd (Rcdnd) was cloned using RACE technology for the first time. In total, the sequence comprises 1339 bp, including a 5′-UTR of 59 bp, a 3′-UTR of 173 bp, and an open reading frame of 1107 bp, encoding a protein of 368 amino acids. The deduced amino acid sequence contains a conserved RNA recognition motif and four conserved regions (CR1~4). Comparisons of the deduced amino acid sequence with those of other teleosts revealed the highest percentage identity (72.3%) with Seriola dumerili. Phylogenetic tree analysis also showed that the dnd of R. canadum was most closely related to the homologous proteins of S. dumerili. Reverse transcription polymerase chain reaction (RT-PCR) results indicated that Rcdnd was specifically expressed in the gonads, but not in other tissues. The results of real-time quantitative PCR (qRT-PCR) revealed that Rcdnd expression tended to gradually increase as the testis developed (Stages Ⅱ to Ⅴ). During the development of the ovary (Stage Ⅰ to Ⅲ), Rcdnd expression first increased substantially and then stabilized; the highest expression level was found at 150 days post hatching (dph) (Stage Ⅱ). Furthermore, the results of chemical in situ hybridization revealed that Rcdnd mRNA was mainly expressed in germ cells but barely detected in somatic cells. In the testis, Rcdnd mRNA signals were concentrated in the periphery of spermatogonia and primary spermatocytes; they were only weakly detected in secondary spermatocytes and barely detected in spermatids and spermatozoa. In the ovary, Rcdnd mRNA was highly expressed in oogonia, and the signals became weak in primary oocytes dispersed in the perinuclear cytoplasm. There were no significant differences in Rcdnd mRNA signals detected in oocytes in phases Ⅰ, Ⅱ, and Ⅲ. In conclusion, these findings suggest that the Rcdnd gene may play an important role in gonadal development and provide a theoretical reference for revealing the regulatory mechanism of germ cell differentiation during gametogenesis in R. canadum.
