Differential analysis of expressed sequence tags from SMART cDNA plasmid libraries of the orange-spotted grouper (Epinephelus coioides) at two different gonadal development stages

The orange-spotted grouper, Epinephelus coioides, is an important marine aquaculture fish and has been cultured in China and Southeast Asian countries. However, large-scale aquaculture of the grouper has been hindered by the rarity of natural males, because it is a protogynous hermaphroditic fish and sex inversion rarely occurs in captive stocks. In teleost fishes, the pituitary plays significant roles in many physiological functions, such as growth and reproduction. In this study, the SMART cDNA plasmid libraries of the pituitaries from orange-spotted groupers, at the early stage of ovary development and the late stage of sex inversion, were constructed. Two hundred and thirty-two and 258 ESTs were obtained from the two pituitary plasmid libraries respectively. Among the two groups of ESTs, the genes homologous to hormones were the most numerous in both groups, accounting for 40.5% and 34.9% of all ESTs respectively. Compared with the level of expression of hormones in the pituitary at the early stage of ovary development, the expression levels of growth hormone (GH), prolactin (PRL). somatolactin (SL) and proopiomelanocortin (POMC) were reduced, and the go-nadotropin common a subunit (GTH alpha), follicle-stimulating hormone P subunit (FSH beta) and luteinizing hormone P subunit (LH beta) were increased at the late stage of sex inversion