Expression of mRNA Encoding IGF-I, IGF-II, Type-I, and II IGF-Receptors and IGF-Binding Proteins-1-4 during Ovarian Follicular Development in Buffalo (Bubalus bubalis)

The present study was designed to investigate the expression pattern of IGF-I, IGF-II, type-I and II IGF-receptors, and IGFBP-1-4 in different stages of buffalo ovarian preantral follicles (PFs), antral follicles (AFs), ovulatory follicles (OFs), and immature (IM) and in vitro matured (MO) oocytes. Buffalo ovaries were collected from local abattoir, PFs (200-250 mu m), AFs (1-3mm), and OFs (5-8mm) were isolated by mechanical method. PFs, AFs, OFs, and oocytes were lysed to release mRNA, reverse transcribed, and then subjected to RT-PCR, whereas protein were localized through immunohistochemistry. Relative expression of mRNA transcripts was clearly seen for IGF-II, type-I and II IGF-receptors, and IGFBP-1-4 in all the stages of developing follicles and oocytes. We were unable to detect mRNA and protein expression of IGF-1 in any of the oocytes or follicles at any stage of the development. IGF-II and both IGF receptors mRNA expression were found higher (P<0.05) in PFs compared to AFs and OFs. Expression of IGFBP-1 and 2 in PFs, as well as IGFBP-3 and 4 in AFs, was found with higher (P<0.05) levels. The expression results were further confirmed by localization of IGF-II, type-I and II IGF-receptors, and IGFBP-1-4 proteins. In conclusion, IGF-II appears to be the only ligand that is endogenously expressed by all the follicular stages and oocytes, which may act in an autocrine manner through the Type-1 IGF receptor. Expression of IGFBP-1-4 and IGF-II suggests the possible role of these genes in recruitment, growth, proliferation, and steroidogenic responses during developmental phases of buffalo ovarian follicles.