AJP - Regulatory, Integrative and Comparative Physiology, Vol 270, Issue 5 1065-R1072, Copyright © 1996 by American Physiological Society
Epidermal growth factor receptor binding and biological activity in the ovary of goldfish, Carassius auratus
D. Pati, K. Balshaw, D. L. Grinwich, M. D. Hollenberg and H. R. Habibi
Department of Biological Sciences, University of Calgary, Alberta Canada.
The receptor binding and biological activity of epidermal growth
factor-urogastrone (EGF) was characterized in the follicle-enclosed
goldfish oocyte. The binding of 125I-labeled mouse EGF (mEGF) to goldfish
ovarian membrane preparation was peptide specific, saturable, reversible,
and dependent on time and tissue concentration. Binding data analysis
indicated the presence of a single class of high-affinity binding sites
with an estimated equilibrium dissociation constant of 4.4 +/- 1.8 x
10(-10) M. The 125I-mEGF binding was displaced by unlabeled mEGF and by
human recombinant transforming growth factor-alpha (hTGF-alpha). Both mEGF
and hTGF-alpha were found to stimulate reinitiation of oocyte meiosis, as
indicated by germinal vesicle breakdown (GVBD). Treatment with mEGF and
hTGF-alpha stimulated GVBD from a basal level of 8.5 to approximately 30%
with an estimated half-maximal effective dose for EGF of 5.80 +/- 0.82 +
10(-10) and for hTGF-alpha, 1.9 +/- 1.0 x 10(-10) M. Furthermore, treatment
with mEGF marginally increased 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one
(DHP)-induced GVBD without significantly influencing the
gonadotropin-induced response. Treatment with either mEGF or hTGF-alpha
significantly reduced human chorionic gonadotropin-stimulated testosterone
production in a concentration-related manner. These data suggest that
members of the EGF family may play a role in the regulation of ovarian
function in goldfish.
