Prominent Expression of Transforming Growth Factor β2 Gene in the Chicken Embryonic Gonad as Revealed by Suppressive Subtraction Cloning

Abstract cDNA cloning from chicken embryonic gonad subtracted from tissues of the brain, heart, liver, gizzard, mesonephros, and muscle was performed to identify growth factor genes with expression unique to embryonic ovary and testis. We obtained several cDNA clones encoding known and many unknown genes. We found for the first time that the transforming growth factor β2 (TGF-β2) is preferentially expressed in the chicken embryonic ovary and testis. cDNA subtraction cloning with respect to the selective expression of TGF-β2 in the ovary and testis was further analyzed by reverse transcription-polymerase chain reaction analyses of other embryonic tissues. The ontogeny of TGF-β2 was evaluated in chicken embryonic ovary and testis. In both testis and ovary, the levels of TGF-β2 transcripts were high during the early period of embryonic development (E7), gradually decreased until the late embryonic days (E14–E17), and then slightly increased at the last embryonic day (E21). There was no difference in the TGF-β2 transcripts per RNA between the left and the right ovaries. TGF-β2 may have a critical role in the regulation of the development of chicken ovarian and testicular germ cells during the embryonic period.