Intraovarian Control of Phenotypes of Granulosa Cells by the Germinal Disc in the Chicken
Yao, Humphrey Hung-Chang
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https://hdl.handle.net/2142/83664
Description
Title
Intraovarian Control of Phenotypes of Granulosa Cells by the Germinal Disc in the Chicken
Author(s)
Yao, Humphrey Hung-Chang
Issue Date
2000
Doctoral Committee Chair(s)
Bahr, Janice M.
Department of Study
Animal Sciences
Discipline
Animal Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Animal Culture and Nutrition
Language
eng
Abstract
Proper interaction between the oocyte and surrounding granulosa cells is essential for development of a healthy follicle for ovulation. My Ph.D. research was devoted to understanding the intraovarian dialogue between the chicken germinal disc, an analog to mammalian oocyte, and its surrounding granulosa cells. My hypothesis was that the germinal disc influences granulosa phenotypes by producing epidermal growth factor (EGF). The major questions were: (1) does the germinal disc produce EGF to regulate granulosa proliferation; (2) is there differential expression of receptors for EGF (EGFr) and luteinizing hormone (LHr) between granulosa cells proximal and distal to the germinal disc; (3) do granulosa cells proximal and distal to the germinal disc respond to EGF and LH differently; (4) how is expression of EGFr and LHr by granulosa cells regulated? I have found that: (1) the germinal disc synthesizes EGF which stimulates granulosa proliferation; (2) granulosa cells proximal to the germinal disc express more EGFr but less LHr than distal granulosa; (3) granulosa cells proximal to the germinal disc proliferate more in response to EGF but they produce less progesterone in response to LH than distal granulosa; (4) expression of EGFr by granulosa cells is not influenced by EGF and LH (except one dose) and expression of LHr by granulosa cells is down-regulated by EGF. I conclude that the germinal disc produces EGF to influence granulosa phenotypes. Granulosa cells proximal to the germinal disc exhibit a proliferative phenotype possibly because they are exposed to and are more responsive to germinal disc derived-EGF. Germinal disc derived EGF further down-regulates LHr expression by proximal granulosa cells and therefore results in less progesterone production in response to LH. In contrast, granulosa cells distal to the germinal disc are not under the influence of EGF and become more differentiated and produce more progesterone in response to LH. This research reveals a paracrine regulation of granulosa phenotypes by the germinal disc. It provides not only a comparative model to strengthen the idea that oocytes play a role in determining the fate of follicles, but also a new perspective on unexplained forms of infertility due to defective oocytes.
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