Author(s): Zhou J, Bievre M, Bondy CA
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Abstract Granulosa cells provide nutritional and trophic support for growing oocytes in ovarian follicles. The granulosa cells closest to the oocyte produce abundant insulin-like growth factor 1 (IGF1) and the IGF1 receptor is highly expressed by oocytes, suggesting that granulosa-derived IGF1 may have trophic effects on oocyte growth and development. To investigate this possibility, in the present study we used in situ hybridization and immunohistochemistry to examine glucose transporter (GLUTs 1, 3 & 4) expression in follicles from pre-pubertal Igf1-/- and littermate wildtype (wt) mice. Pre-pubertal mice were used for this study because the Igf1 null mice do not mature sexually. GLUT1 mRNA and immunoreactivity were most abundant in oocytes and in granulosa cells immediately surrounding the oocyte. Expression of this transporter was significantly reduced in Igf1 null oocytes and granulosa cells and was restored by exogenous IGF1 treatment to wt levels. These effects on GLUT expression were significant at both the mRNA and immunoreactive protein levels. Oestrogen treatment significantly increased GLUT1 levels in oocytes and granulosa from both wt and Igf1-/-, although the latter were still significantly lower than wt. Oocyte glycogen stores, determined by PAS staining, did not appear different in Igf1-/- and wt mice.GLUT3 was expressed in thecal cells surrounding growing follicles and was not appreciably different in Igf1 null compared with wt ovaries. GLUT4 expression was not detected in the prepubertal mouse ovary. Together with observations from previous studies showing that ovulation is blocked in Igf1 null mice, the present data suggest that IGF1's augmentation of granulosal and oocyte GLUT1 expression may be essential for oocyte maturation and successful ovulation. Copyright 2000 Harcourt Publishers Ltd.
This article was published in Growth Horm IGF Res
and referenced in Journal of Steroids & Hormonal Science