Cloning DMO CDNA Of Oreochromis Aurea And Preliminary Study Of Sex-Determining Mechanism In Tilapia

Tilapia is tropical fish from Africa. It has been the popular farming variety in the world. In farming, the male growths more quickly than the female by 40-50%, so it is very important to enhance the male rate. In the hybrid combinations of tilapia, the offspring of Oreochromis aurea( ) and Oreochromis niloticus() has more males which rate is 95%, but the male rate should be 100% according to the chromosomal theory. Sex determination and differentiation in fish is highly variable and complicated, so we may reveal the sex regulatory mechanism and improve the male rate through researching on molecular biology in tilapia.DMO gene is one of DMRT genes which have been found in mammals, a reptile, a bird and fish as a sex determination gene. DMRT genes constitute a family of genes, which possess a common motif called the DM domain. The DM-domain is a DNA-binding motif shared between Drosophila doublesex and C. elegans mab-3. Both doublesex and mab-3 play key roles in sex determination. At present, SRY/Sry and sox genes have not been found in fish, but DMRT gene exists in fish. In this study, we analyse DMO gene and DMRT gene for further studying sex correlative determination gene in tilapia.A two-phase rapid amplification of cDNA ends (RACE)-PCR was used for the isolation of the full length cDNA of DMO(DM-domain gene in Ovary) from ovary of Oreochromis aurea. We amplified a fragment about 1217bp by 3' RACE-PCR and sequenced it. Basing upon this sequence we designed gene-specific primers for 5' RACE-PCR which yielded a fragment about 455bp. Sequence analysis revealed a 1571bp cDNA containing the 148bp 5'-untranslated region, 193bp3-untranslated region and 1230bp open reading frame encoding 409 amino acid. Sequence analysis revealed homology of DMO in Oreochromis aurea and Oreochromis niloticus is 96.3%. However, we compare the alignment of deduced ammo acid sequences between DMO cDNA from Oreochromis aurea and DMRT1 (DM-related transcription factor 1 )cDNA from Oreochromis niloticus, fugu, rainbow trout, medaka, rat and human. The score is 25.7%, 25.8%, 24.3%, 29.7%, 22.5% and 22.0% respectively. These results indicated that DMO and DMRT1 gene may be different genes.