Male-specific Dmrt1 is a candidate sex determination gene in spotted scat (Scatophagus argus)

The Scatophagus argus is a cultured marine teleost fish in which females grow faster and larger than males, therefore cloning the master sex-determination (SD) gene will be helpful for its sex control in aquaculture. A well-conserved Dmrt1 (doublesex- and mab-3-related transcription factor-1) gene, encoding zinc finger-like DNA binding motif (DM-domain) plays a critical role in sex determination and differentiation in vertebrates. Here, two pairs of sex-specific primers, Dmrt3-Marker-F/R and Dmrt1-Marker-F/R were developed from Dmrt3 and Dmrt1 transcripts in S. argus respectively. The single-nucleotide polymorphisms (SNP) at position −151 and 166 bp on the DNA amplified by Dmrt3-Marker-F/R are all homozygous CC GG genotype in females and heterozygous CG GA genotype in the males. The Dmrt1-Marker-F/R could only amplify a 3.2 kb fragment in males. Both Markers were confirmed in 246 adult S. argus (113 males and 133 females) from five populations in China. These results indicate that the sexes of S. argus are controlled by sex chromosomes (XX females, XY males). The nucleotide at position 166 bp of the DNA amplified by Dmrt3-Marker-F/R is found to be a donor splice site mutation (c.400 + 1G > A) in Dmrt3 which generates a truncated isoform. The truncated Dmrt3 is linked to male sex and thereafter named as Dmrt3△-Y, and its allele is the normal Dmrt3 on the X chromosome. The DNA amplified by Dmrt1-Marker-F/R is a fragment between exon 2 and exon 3 of a normal Dmrt1 implying that Dmrt1 is male-specific and located on the Y chromosome. A truncated Dmrt1 (Dmrt1b) was found to exist in both males and females. The Dmrt1b is with high similarity with Dmrt1 indicating Dmrt1b is the allele of Dmrt1 located on the X chromosome. RT-PCR revealed that Dmrt1 is highly expressed in the testes, while it is not expressed in the ovaries. Dmrt3△-Y is only expressed weakly in some of the testes, while it is not expressed in the ovaries. The testicular specifically expressed Dmrt1 is the candidate SD gene on the Y chromosome in S. argus.