Enhanced expression of β-thymosin mRNA in the ovary of GnRH analog or estradiol-17 β-treated paradise fish, Macropodus opercularis

Abstract

cDNA clones were isolated as expressed sequence tags (ESTs) from the ovarian cDNA library of Macropodus opercularis. The EST sequences showed similarity with many housekeeping genes and ribosomal proteins. One of the ESTs showed similarity to β-thymosin, a 5-kDa polypeptide expressed under different physiological conditions. The cDNA corresponding to β-thymosin of M. opercularis is 368 bp in length and codes for a putative polypeptide of 42 amino acids. Multiple alignment of the deduced amino acid sequence showed 61% similarity with piscine β-thymosins and 56% similarity with mammalian β-thymosins. Administration of a gonadotropin releasing hormone analog or estradiol-17β induced an increase in the gonadosomatic index, oocyte diameter and also enhanced expression of β-thymosin m-RNA in the recrudizing ovary. This report indicates that both GnRH analog and E₂ might induce similar pathways for the differentiation of ovarian cells for the maturation of oocytes.