Identification of differential genes in the ovary relative to the testis and their expression patterns in half-smooth tongue sole (Cynoglossus semilaevis)

Half-smooth tongue sole (Cynoglossus semilaevis) is a rare marine flatfish whose mature ovary and testis greatly differ in volume and weight. The length and weight of mature females are over twice greater than those of mature males. To obtain sufficient information on gonad differentiation and the relationship between gonad development and growth in the fish, we compared gene expression between the ovary and testis using suppression subtractive hybridization (SSH). Testis cDNAs are subtracted from ovary cDNAs and are used to establish an ovary testis-subtracted cDNA library. A total of 41 nonredundant clones are identified, including 20 known cDNAs, 9 uncharacterized cDNAs (EST clones), and 12 novel sequences. For selected genes such as ZPC, RacGAP, survivin, aquaporin, CPEB, O5, O15, and O18, gene expression patterns are analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR). The results confirm that these genes are only expressed in the ovary and not in the testis, or at higher levels in the ovary than in the testis. At the same time, expressions of certain genes such as ZPC, survivin, aquaporin, CPEB, and O15 are demonstrated to possess sexual dimorphism in the kidney or muscle, and spleen. The results suggest that these genes could play key roles not only in the ovary but in other female tissues as well.