Studies On Growth And Development Of The Ovarian Dominant Follicle In Monovulatory Species : Analysis Of Transcriptional Changes And Factors Influencing Periovulatory Events

Abstract

In response to LH surge, the selected dominant follicle undergoes a series of complex events viz., meiotic maturation of the oocyte, terminal differentiation of follicular cells, cumulus expansion and follicular rupture leading to ovulation (release of fertilizable oocyte) and formation of corpus luteum. These complex set of events are mediated by dramatic changes in the temporo-spatial transcriptional regulation of a large number of genes in the preovularory follicle. In the present thesis, attempts have been made to delineate the transcriptional changes occurring in the periovulatory follicle in response to gonadotropin surge in monovulatory species (bonnet monkeys and buffalo cows). Further, attempts have also been made to investigate effects of increased circulating IGF-I and glucose on the periovulatory events. Chapter I provides a review of available literature on regulation and factors influencing various aspects of growth and development of ovarian follicles. Chapter II describes initial studies carried out in the bonnet monkeys to examine expression patterns of various genes considered as markers of ovulation and luteinization in granulosa cells of multiple preovulatory-like follicles before and after exposure to luteinizing dose of hCG. Chapter III describes the standardization and validation of an induced ovulation model system in buffalo cows involving determination of the presence of a large follicle by ultrasonography before administering exogenous PGF2αon day 7 of the cycle to induce luteolysis and administration of hCG 36 h post PGF2αto mimic LH surge-like stimulus. Attempts made to characterize the responsiveness of buffalo cows to a range of exogenous doses of GnRH in terms of LH secretion during summer and winter seasons and determination of the exogenous dose of GnRH necessary to elicit a surge-like increase in circulating LH levels during breeding season in buffalo cows are described in Chapter IV. Chapter V describes the global changes in the gene expression pattern in the periovulatory follicle of buffalo cows before and at various time points after the onset of gonadotropin surges. IGF-I is known to regulate the proliferation and survival of follicular cells and play an important role in the selection of dominant follicle however, its role during the periovulatory events remains to be delineated. Chapter VI describes the effects of increased circulating and intrafollicular IGF-I levels on the periovulatory events. An ongoing study to delineate the effects of transient increase in circulating glucose levels on the periovulatory events are described in Appendix I. Thus, this thesis aims at delineating (i) changes in the gene expression patterns regulating periovulatory events and (ii) effects of increased circulating IGF-I and glucose on the periovulatory events.