PARENT SESSION
Hormone Receptors

EXPRESSION OF ESTROGEN RECEPTOR -ALPHA (ER) AND ESTROGEN RECEPTOR-BETA (ER) IN THE HAMSTER OVARY THROUGHOUT THE ESTROUS CYCLE: HORMONAL REGULATION.

Yang, Peixin¹, Roy, Shyamal^1,2, ^{1 2}

ABSTRACT- Estrogen action on ovarian cells involves two major types of nuclear receptors, namely ERa and ERb. Although estrogen binding has been demonstrated in the hamster ovary, virtually nothing is known about the expression of estrogen receptor subtypes in follicular cells during development. To determine the spatial distribution and the role of endogenous hormones on ovarian ERa and ERb expression, immunofluorescence and immunoblot analyses were done on hamster ovaries collected at 0900 on estrous D1 through D4, and at 16:00 on D4. ERa fluorescence was present in all ovarian cells, including granulosa cells (GC) of preantral and antral follicles. Expression of ERa in interstitial cells (IC) and GC of large preantral follicles increased from D1 through D3 and decreased by D4:0900h corresponding to increase in serum estrogen levels. For antral follicles, a preferential increase in the intensity was noted in the antral GC from D2 through D4, followed by a sharp decrease after the LH surge. A decrease was also evident for IC following the LH surge. Although, intense ERb immunoreactivity was primarily localized in the GC of follicles at all stages, in contrast to rats and mice, modest expression was evident in thecal and interstitial cells. The expression of ERb in the GC followed the same pattern as that of ERa during the cycle. Immunoblot analysis of theca and GC of preovulatory follicles, and IC confirmed the presence of a 65 kDa ERa and a 50 kDa ERb in these cells. Next, the selective role of hormones on ovarian ERa and ERb expression was evaluated using ovaries of hypophysectomized hamsters. A modest increase in ERb expression in the GC but a noticeable increase in ERa expression in the IC was evident in response to FSH. In contrast, hCG down-regulated the expression even in the presence of FSH. Whereas Estradiol significantly induced both ERa and ERb expression in GC of preantral follicles, P attenuated Estradiol effect. These results suggest that ER expression in follicular and non-follicular cells is differential and undergoes changes along with follicular development under endogenous hormonal milieu. Further, a critical ratio of Estradiol and P may determine the magnitude of estrogen effect on follicular cells by modulating the expression of ERb in GC of all follicles and of ERa during antrum formation.

KEY WORDS: hamster, estrogen receptor, ovary, follicle