KOHLI, G; CLELLAND, E; DIMUCCIO, T; PENG, C; York Univerity; York University; York University; York University: Transforming growth factor-�1 in zebrafish ovary: cDNA cloning, mRNA expression and role in oocyte maturation

Transforming growth factor-� (TGF-�) is a multifunctional factor involved in regulating a variety of cellular activities. In mammals, TGF-� in known to regulate reproduction, including ovarian functions. The role of TGF-� in lower vertebrates is poorly understood. To examine the role of TGF-� in fish reproduction, we have cloned the cDNA encoding TGF-�1 from the zebrafish ovary and determine mRNA levels of TGF-�1 during follicle development. In addition, the role of TGF-�1 in final oocytes maturation was also examined. The zebrafish TGF-�1 has 377 amino acids, of which 112 is the mature peptide. The mature peptide region of zTGF-�1 shows 70-80% identities with TGF-�1 from other species and exhibits all characteristics of the TGF-� family. To measure TGF-�1 mRNA levels, total RNA was extracted from different stages of follicles and reverse transcribed. Relative mRNA levels were determined using real-time PCR. TGF-�1 mRNA levels were low in pre-vitellogenic follicles, increased in small vitellogenic follicles and reached the highest in fully developed vitellogenic follicles. In mature follicles, TGF-�1 mRNA levels significantly declined. The effect of TGF-�1 on oocyte maturation was studied by incubating follicles with TGF-�1, either alone or in combination with hormones such as MIH & hCG. TGF-�1 slightly inhibited the rate of spontaneous and hCG-induced maturation. Interestingly, TGF-�1 significantly inhibited MIH-induced maturation, suggesting that TGF-� may inhibit targets downstream of MIH. Taken together, this study demonstrates that TGF-�1 is expressed in the zebrafish ovary and that TGF-�1 inhibits oocyte maturation. These findings suggest that TGF-�1 is a local factor involved in regulating ovarian functions in fish.