Abstract
This thesis focuses on protein and mRNA expression of growth factors in goat ovaries and on in vitro culture of primordial and primary follicles. In Chapter 1, a review of local growth factors, including activin-A, follistatin, growth differentiation factor-9 (GDF-9), bone morphogenetic protein-15 (BMP-15), Kit Ligand (KL) and their receptors
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was described. In Chapter 2, using immunohistochemistry and RT-PCR, protein and mRNA for activin-A, follistatin and their receptors were demonstrated in ovarian follicles at different stages of development. Activin-A and follistatin proteins were found in oocytes of all follicle classes, granulosa cells from the primary follicle stage onwards, theca cells of antral follicles, corpora lutea and ovarian surface epithelium. In antral follicles, these proteins were detected both in cumulus and mural granulosa cells. Proteins and mRNA for activin receptors were generally found if follicles at all stages of development. In Chapter 3, the effects of activin-A and follistatin on the development of primordial and primary follicles cultured in vitro were investigated to find additional evidence for their role in early folliculogenesis. Activin-A treatment enhanced the number of normal follicles and stimulated their growth during cortical tissue culture. These effects were, however, not counteracted by follistatin. Addition of activin-A to cultured isolated primary follicles significantly stimulated their growth, the effect being counteracted by follistatin. In Chapter 4, we studied the presence and distribution of GDF-9 and BMP-15 and their receptors, the BMP receptors types II (BMPR-II), IA (BMPR-IA) and IB (BMPR-IB), in goat ovaries. GDF-9 and BMP-15 proteins were found in oocytes of all types of follicles and granulosa cells of primary, secondary and antral follicles but not in those of primordial follicles. The mRNAs for GDF-9, BMP-15, BMPR-II, BMPR-IA and BMPR-IB were detected in primordial, primary and secondary follicles as well as in oocytes and granulosa cells of antral follicles. Transcripts for BMPR-II, BMPR-IA, BMPR-IB and GDF-9, and GDF-9 protein were furthermore found in corpora lutea. In Chapter 5, KL and its receptor, c-Kit, were studied. KL protein and mRNA was found in follicles at all stages of development, i.e., primordial, primary, secondary, small and large antral follicles, as well as in corpora lutea, ovarian surface epithelium and ovarian medullary tissue. Antral follicles expressed both KL-1 and KL-2 mRNAs, while earlier staged follicles expressed KL-1 transcript only. c-Kit mRNA was expressed at all stages of follicular development and in all antral follicular compartments. c-Kit protein was predominantly found in oocytes from the primordial follicle stage onwards, in theca cells of antral follicles. Finally, Chapter 6 contained an overview and a discussion of the main results of this thesis. It was concluded that the mRNAs of activin-A, its receptors and its binding protein follistatin are expressed and their proteins formed at all follicular stages. Activin-A promotes in vitro survival and growth of activated follicles in cortical tissue, but in cultured isolated primary follicles it only promotes their growth and not the survival. KL, c-Kit, GDF-9, BMP-15 and BMP receptors are expressed in goat ovarian follicles at all stages of their development.
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