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The role of the IGF system in somatic cell and oocyte development during early bovine follicular development

The aims of this thesis were to use a serum-free culture system to investigate the role of the IGF system during early bovine follicular development. The study focused on investigating the actions and regulation of IGF in three key stages of follicle growth. These key stages were: primordial follicle initiation, the transition from preantral to antral stages, and early antral follicle growth. No effects of IGF-I on primordial follicle initiation or activated follicle growth were found, but IGF-1 that was not regulated by IGFBPs was found to have a negative effect on the oocyte health of growing follicles after 6 days of culture. Hence, during the early stages of follicle development the regulation of the bioavailability of IGF is crucial to maintain the health of the oocyte. A 6 day culture of bovine early antral follicles in the presence of IGF-1 was found to stimulate both follicle proliferation in the early stages of development, and differentiation at all developmental stages, as exhibited by oestradiol production. Furthermore, these effects were found to occur in a dose and stage dependent manner. Additionally, oocyte health was improved by the addition of recombinant IGF-I in the more mature antral follicles. These results highlight the importance of follicle developmental stage when deciding the best in vitro culture conditions. The biological actions of IGF depend in part on the ability of specific proteases to break down the IGF/IGFBP complex. The secretion of proteases capable of degrading IGFBP-2 by different bovine follicular compartments was identified, and the effect of IGF-1 and/or follicle stimulating hormone (FSH) on modulating IGFBP-2 proteolytic degradation was also investigated. Proteolysis of IGFBP-2 caused by the incubation of IGFBP-2 with oocytes was not detected. However, incubation of IGFBP-2 with granulosa cells did cause a small level of IGFBP-2 degradation. The ability of IGF-1 and FSH to enhance or inhibit the degradation of IGFBP-2 was also studied. The use of a serum-free culture system in this study has improved our understanding of how the complex IGF system is regulated throughout bovine follicular development. It has highlighted that the regulation of IGF bioavailability to a growing follicle is governed by different levels of regulation, such as the level of expression and degree of proteolysis of IGFBPs, which are follicle stage dependent. A fuller understanding of the mechanisms that control the access and regulation of local growth factors will allow us to move closer to developing an in vitro culture system capable of producing large numbers of viable oocytes for use in reproductive technologies.
Date January 2005
CreatorsWalters, Kirsty Anne
PublisherUniversity of Edinburgh
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation

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