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Regular Article |
a Departments of Obstetrics and Gynecology, Leland J. and Dorothy H. Olson Center for Women's Health,
b Physiology and Biophysics, University of Nebraska Medical Center, Omaha, Nebraska 68198-4515
ABSTRACT
Epidermal growth factor (EGF) is mitogenic to preantral follicles, and transforming growth factor ß (TGFß) influences ovarian cell functions in a variety of species. Although an interaction of these ligands during preantral folliculogenesis is likely, whether EGF influences TGFß action on preantral follicles by modulating TGFß receptor (TßR) gene transcription and translation is not known. To determine whether EGF influenced TßR mRNA and protein levels in granulosa cells during preantral folliculogenesis, hamster preantral follicles at stages 1–6 were cultured in the absence or presence of EGF and follicular TßR mRNA, and protein levels were monitored by semiquantitative reverse transcription polymerase chain reaction and immunoblotting, respectively. Both TßR type I (TßRI) and TßR type II (TßRII) mRNA and protein were present in preantral follicles, and their expression was up-regulated by EGF in a stage-dependent manner. However, EGF effect on the expression of TßRI and TßRII was differential. In contrast to TßRI, EGF-stimulation of follicular TßRII mRNA expression was evident from stages 1 and 2 onwards, and more than twofold induction was noted for stages 4–6. Moreover, significant increases in thecal TßR mRNA levels were noted for stage 6 follicles. Follicles at smaller stages appeared to be more sensitive to EGF than were larger preantral follicles. Despite an increase in the cytosolic form of TßRI protein for most of the stages and TßRII protein for follicles at stages 4 and 5, EGF-stimulation of the membrane-associated form of the receptor was restricted to follicles at stage 6. Functionally, TGFß1 attenuated EGF-induced DNA synthesis for follicles at stages 1–3 and 6 without affecting EGF-induced progesterone production for most of the stages. Administration of
-amanitin resulted in a significant reduction of EGF-induction of TßR mRNA levels, suggesting that increased receptor protein levels were a consequence of mRNA synthesis. These results indicate that an interaction between EGF and TGFß forms an important regulatory mechanism for preantral folliculogenesis. The effect of EGF on TßRI and TßRII gene transcription and translation are differential, and follicular response to EGF depends on the developmental status of the follicles.
First decision: 19 January 2001.
1 This study was supported by a grant (HD28165) from NICHHD and the Olson Foundation of Omaha. A portion of this work has been presented at the 33rd Annual Meeting of the Society for the Study of Reproduction at Madison, Wisconsin.
2 Correspondence: S.K. Roy, Departments of OB/GYN and Physiology and Biophysics, University of Nebraska Medical Center, 984515 Nebraska Medical Center, Omaha, NE 68198-4515. FAX: 402 559 6164; skroy{at}unmc.edu
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