As a functional unit involved in both maintaining endocrine homeostasis and also producing mature eggs, the ovary plays a central role in female reproduction. The development and function of the ovarian follicles are controlled by gonadotropins released from the pituitary. It is widely accepted that the action of gonadotropins on ovarian follicles is mediated by paracrine/autocrine factors produced by the somatic cells surrounding the oocyte. Increasing evidence indicates that the Igf system is involved in mediating the action of gonadotropins in the ovary. Previously, we identified a gonad-specific Igf subtype (Igf3) distinct from Igf1 and Igf2. This fmding further highlights the importance of the Igf system in the fish ovary. In this thesis, efforts were made to understand the role of the Igf system in ovary using zebrafish as the model organism, and attention was focused on Igf3. / Because the expression of Igf3 is correlated with the LH receptor in zebrafish follicles, the regulation of igf3 by gonadotropins was subsequently studied in the ovary. The expression of igf3 was significantly up-regulated in both ovarian fragments and isolated follicles upon treatment with hCG in dose- and time-dependent manners. Treatment with 8-Br-cAMP or IBMX mimicked the effects of hCG on the expression of igf3 in follicles of different stages. / Four Igfs are present in zebrafish, and our results show that all four igfs are expressed in the ovary of zebrafish and exhibit the differential expression profiles during folliculogenesis. Using a primary culture of zebrafish follicle cells, we demonstrated that hCG stimulated igf2b and igf3 expression but suppressed igf2a expression. Moreover, the effect of gonadotropin could be mimicked by IBMX, which increased the intracellular levels of cAMP, suggesting the possible involvement of cAMP in the gonadotropin-based regulation and differential expression of igf2a, igf2b and igf3. These results also show that the Igf3 is the Igf subtype most sensitive to gonadatropin and cAMP. / In addition, the expression patterns of igf1, igf2a, igf2b, igf3, igf1ra and igf1rb were also studied during zebrafish embryogenesis. The unique temporal and spatial expression patterns of igf1, igf2a, igf2b, igf3, igf1ra and igf1rb were revealed by both real-time PCR and whole mount in situ hybridization, the results suggest divergent functions for these Igfs in early zebrafish development. / Taken together, the present studies provide substantial information about the Igf system, especially that of Igf3 in the zebrafish ovary. Data were gathered regarding Igf3 expression, regulation and functions, which is not only helpful for the understanding of the role of the Igf system in fish reproduction, but also contributes toward uncovering the ovarian signaling network involved in oocyte maturation across vertebrates. This study of igfs gene expression provides direct information to the study of Igf signaling in zebrafish. / To study the function of Igf3, bioactive recombinant Igf3 proteins were prepared using a bacterial expression system. Incubation of follicles with recombinant zebrafish Igf3 significantly enhanced oocyte maturation in time-, dose- and stage-dependent manners. The potential mechanisms of Igf3-induced oocyte maturation were then investigated. Igf3 stimulated oocyte maturation via a steroid-independent manner. Igf3 induced oocyte maturation through Igf1rs and the PI3 kinase, PDE3 and MAP kinase were necessary for Igf3-mediated oocyte maturation in zebrafish. / We first examined the gene expression patterns of Igf3 in the ovary. The igf3 gene in zebrafish was found to be alternatively spliced into two transcripts, with transcript variant 1 exclusively expressed in the gonads and transcript variant 2 only expressed during early development. Using specific antibodies developed for zebrafish Igf3, both the prepropeptide and the mature peptide forms of Igf3 were found to be predominantly expressed in the zebrafish ovary. Real-time PCR and in situ hybridization revealed that igf3 mRNA levels were relatively low in the early follicles but significantly increased after the mid vitellogenic stage (midstage III) and were high in the full grown follicles. In the full grown follicles, igf3 mRNA was detected primarily in the somatic follicular cells, with a low level of expression in the oocytes. Igf3 immunoreactivity was confined to the follicular cells alone. / Li, Jianzhen. / Advisers: Hui Zhao; Hon Ki Christopher Cheng. / Source: Dissertation Abstracts International, Volume: 73-06, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 122-150). / 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.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_344978 |
| Date | January 2011 |
| Contributors | Li, Jianzhen, Chinese University of Hong Kong Graduate School. Division of Biochemistry. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, theses |
| Format | electronic resource, microform, microfiche, 1 online resource (xvii, 150 leaves : ill. (some col.)) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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