Finally, as the first step to study the regulation of Kit system, we found that IGF-I was a potent regulatory factor that up-regulated the expression of kitlga in zebrafish follicle cells. The stimulation involved transcription but not translation, indicating that the kitlga gene is a direct downstream target of IGF-I. The effect of IGF-I on kitlga was exerted via PI3K-Akt but not MAPK pathway. In contrast, the MAPK pathway may play a negative role in controlling kitlga expression. / Kit ligand (also named stem cell factor, SCF) is a pleiotropic growth factor with diverse biological functions. It exerts effects on target cells by binding to its cognate tyrosine kinase receptor, Kit. In mammals, accumulated evidence has demonstrated important roles for Kit ligand and Kit in gametogenesis, melanogenesis and haematopoiesis. However, very little is known about Kit system in other vertebrates. In the present study, we used zebrafish as the model to investigate the expression, regulation and function of the Kit system in the ovary. / On the other hand, cAMP is involved in regulating the expression of kitlga in zebrafish follicle cells. Two cAMP-activated effectors, PKA and Epac, have reverse effects. PKA promotes but Epac inhibits the expression of kitlga, which was identified by the respective activator. The effect of forskolin and H89 on IGF-I-induced expression of kitlga suggests a cross-talk between the two signaling pathways. Both hCG and PACAP inhibited IGF-I-induced kitlga expression, indicating that they may have negative regulation through cAMP signaling pathways in the full-grown follicles. (Abstract shortened by UMI.) / The zebrafish has two homologues of Kit ligand (kitlga and kitlgb) and Kit (kita and kitb ) instead of one copy for each as in mammals. The present study proposed the origin of these homologues in the zebrafish by phylogenetic and chromosome synteny analyses, and provided further evidence for neo- or subfunctionalization for both Kit ligands and Kit receptors in the zebrafish ovary. All four Kit system members exhibited distinct and significant changes in mRNA expression during folliculogenesis, particularly in the periovulatory period before and after final oocyte maturation and ovulation. / Then we further studied the spatial localization of each member within the follicle. The present study demonstrated that kitlga and kitb are exclusively expressed in the follicle layer, while kitlgb and kita only in the oocyte. Using CHO cell line as a bioreactor, we produced recombinant zebrafish Kitlga and Kitlgb. Analysis in mammalian COS-1 cells and zebrafish primary follicle cells confirmed their biological activity and binding specifity. Two opposite paracrine pathways of Kit system in the zebrafish ovary have been shown. Kitlga from the follicle cells preferably activates Kita in the oocyte in spite of the weak response of Kitb to it. Kitlgb from the oocyte, however, exclusively activates Kitb in the follicle cells without any effects on Kita. / Yao, Kai. / Adviser: Ge Wei. / Source: Dissertation Abstracts International, Volume: 73-02, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 136-150). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.