Identification of a candidate sex-determining gene, ptf1aY, in the Chinese longsnout catfish (Leiocassis longirostris) through high-throughput sequencing

Abstract

Identifying sex-specific molecular markers and elucidating sex determination mechanisms are critical in sex-controlled breeding in aquaculture. Chinese longsnout catfish (Leiocassis longirostris) is characterized by rapid male growth, suggesting that all-male production will be economically desirable in aquaculture. In this study, novel sex-specific sequences were identified in the Chinese longsnout catfish by using comparative genomics with high-throughput sequencing. Based on the variable regions between the X (1513 bp) and Y (862 bp) sequences, a pair of Y-specific primers was designed to discriminate the genetic sex of Chinese longsnout catfish. The specificity and universality of these primers were verified in two breeding and three wild populations. Sequence analysis revealed that the 1513 and 862 bp were pancreas transcription factor 1a (ptf1a) homologous genes, implying that Chinese longsnout catfish possess an XY sex-determination system, with ptf1a as the sex-linked gene. Two ptf1a cDNA sequences were isolated and named ptf1aX and ptf1aY based on their sites on the X and Y chromosomes. The ptf1aY gene is a truncated copy of ptf1aX on the Y chromosome. The proteins encoded by ptf1aX (263 aa) and ptf1aY (199 aa) showed high sequence identity (65.40 %). Expression analysis showed that ptf1aY mRNA was specifically detected in the testes, and ptf1aX was expressed in the both ovaries and testes. Thus, ptf1aY is a candidate male sex-determining gene in the Chinese longsnout catfish. Our study greatly contributes to understanding sex determination mechanisms and developing all-male population of Chinese longsnout catfish.