Identification and biosynthesis of sperm receptor in quail oocyte

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The avian oocyte is bounded by the thin translucent membrane called vitelline membrane. The vitelline membrane consists of three layers, the inner and outer layers and the continuous membrane. Only the inner layer of vitelline membrane surrounds the oocyte at the time of ovulation. We have found that the granulosa cells of the preovulatory follicles contain 33 kDa glycoprotein (ZPC) one of the major components of the inner layer in quail egg. Though the physiological importance of ZPC for fertilization was pointed out as the candidate of "sperm receptor" in quail, the details in the regulation of ZPC production in granulosa cells during ovulation cycle remains obscure. To investigate the regulatory mechanism of ZPC production we have studied the expression of ZPC during the ovulation cycle by Western blot and Northern blot analyses. Moreover, we cultured the granulosa cells with or without various hormones and growth factors to study the endocrine and paracrine control of ZPC production. From the Western blot and Northern blot analyses in in-vivo study, the expression of ZPC in the granulosa cells of growing follicles increased during follicular maturation with the highest activity in the largest follicle. To investigate the effects of various hormones and growth factors on the ZPC production, the granulosa cells obtained from the three largest follicles were cultured for 72 hr with FSH, LH, EGF, IGF- I, IGF- II, TGF- alpha, TGF- beta, progesterone, estradiol, or testosterone. The most prominent effects on stimulation of ZPC production was observed in the granulosa cells isolated from the third largest follicle cultured by the addition of FSH.Other hormones or growth factors caused no significant increase. These data illustrate that quail granulosa cells produce ZPC in response to FSH.