Profile analysis of expressed sequence tags derived from the ovary of tilapia, Oreochromis mossambicus

Precise regulation of gene expression is required for a proper transition through the different phases of the ovarian cycle. To study ovarian gene expression in teleosts, we constructed an adult ovary cDNA library of tilapia, Oreochromis mossambicus, and analyzed the gene expression profile using an expressed sequence tag-based strategy. Of 768 random clones, 530 clones, with insert lengths of > 100 base pairs (bp), were assembled into 474 tentative unique genes (TUGs), including 34 contigs and 440 singlets. Among these, 230 TUGs were highly homologous to known genes in public databases, while others exhibited a low sequence homology or no significant matches to known sequences; these are called novel genes here. The abundance of each identified gene was assayed to evaluate its relative importance in ovarian functions. In addition, we analyzed the expression patterns for 6 development-and reproduction-related genes, including cofilin, fibulin-4, glucosamin-6-phosphate deaminase 2 (GNPDA), MCM-6, stathmin, and zona pellucida C5 (ZPC5), as well as 9 novel genes. Results showed that GNPDA, MCM6, ZPC5, and 7 of the novel genes, including O34, O141, O148, O149, O243, O258, and O319, were predominantly expressed in the ovary and/or testis. In addition, the expression patterns of gonad-specific novel genes in tilapia larvae were differentially affected by treatment with 17 β-estradiol and 17 α-methyltestosterone during the sex-sensitive period.