The aim of the present study was to investigate the stability of six housekeeping genes, and the relative expression of growth factors (EGF, GDF-9, BMP-15, VEGF, FGF-2, BMP-6, IGF-1 and KL) and hormone receptors (FSH, LH and GH) in goat preantral follicles. To evaluate to stability of housekeeping genes micro-dissected fresh follicles (150-200 μm) as well as follicles that have been in vitro cultured for 12 days were used. In addition, isolated fresh follicles were used to compare expression of various growth factors and hormone receptors before culture. Both fresh and cultured follicles were subjected to total RNA extraction and synthesis of cDNA. After amplification of cDNA by real-time PCR, the geNorm software program was used to evaluate the stability of glyceraldehyde-2-phosphate dehydrogenase (GAPDH), β-tubulin, β-actin, phosphoglycerokinase (PGK), 18S rRNA, ubiquitin (UBQ) and ribosomal protein 19 (RPL-19). In addition, follicular steady-state levels of mRNA from the various growth factors under study were compared. Results demonstrated that, in goat preantral follicles, UBQ and β-actin were the most suitable reference genes and thus could be used as parameters to normalize data from future in vitro studies. In contrast, 18S RNA appeared the least stable gene among the tested housekeeping genes. Analysis of mRNA for several hypophyseal hormone receptors in fresh preantral follicles showed significantly higher FSH-R mRNA levels than those of LH-R and GH-R, and no difference between GH-R and LH-R mRNA levels. In regard growth factor mRNA expression in goat preantral follicles, EGF mRNA levels appeared significantly lower than those of the other studied growth factors. Increasingly higher relative mRNA levels were observed for GDF-9, BMP-15, BMP-6, FGF-2, VEGF, Kl and IGF-1, successively. In conclusion, UBQ and β-actin are the most stable housekeeping genes in fresh and 12-days cultured caprine preantral follicles. Furthermore, in fresh follicles, high levels of FSH-R mRNA are detected while among eight growth factors, IGF-1 is the most highly expressed and EGF the weakest expressed compound.

Expression of BMP-6 mRNA was quantified by real-time polymerase chain reaction (PCR) and the BMP-6 protein was demonstrated by immunohistochemistry in the primordial, primary, secondary, small and large antral follicles of goat. Furthermore, the influence of BMP-6 on increase in diameter, antrum formation and expression of BMP-6 and FSH-R in in vitro cultured secondary follicles was studied. Therefore, goat primordial, primary and secondary follicles, as well as small and large antral follicles were obtained and the mRNA levels of BMP-6 were quantified by PCR in real time. Expression of BMP-6 protein in goat follicles was demonstrated by immunohistochemistry. The influence of BMP-6 in the presence or absence of follicle-stimulating hormone (FSH) on both the development of secondary follicles and the expression of mRNA for BMP-6 and FSH-R was evaluated after 6 days of culture. Furthermore, the follicular diameter and the formation of the antrum were evaluated before and after 6 days of culture and compared by Kruskal-Wallis and chi-squared tests (P < 0.05), respectively. The results show that the level of mRNA for BMP-6 in primary and secondary follicles was significantly higher than in the primordial follicles (P < 0.05). Similar levels of BMP-6 mRNA were observed in cumulus-oocyte complexes and mural granulosa/theca cells from small and large antral follicles, respectively. BMP-6 protein was expressed in oocytes of all categories of follicles and in granulosa cells from secondary follicles onwards. Addition of BMP-6 to the culture medium increased the diameter of secondary follicles mainly by antrum formation after 6 days' culture, in the presence or absence of FSH (P < 0.05). Furthermore, addition of FSH resulted in increased levels of BMP-6 mRNA in these follicles (P < 0.05). Simultaneous administration of FSH and BMP-6 enhanced the levels of FSH receptor (FSH-R) mRNA (P < 0.05). It is concluded that BMP-6 mRNA is increased during transition from primordial to primary/secondary follicles in the goat ovaries and that BMP-6 enhances the growth of cultured secondary follicles.

The bone morphogenetic protein (BMP) family consists of several growth factor proteins that belong to the transforming growth factor-β (TGF-β) superfamily. BMPs bind to type I and type II serine-threonine kinase receptors, and transduce signals through the Smad signalling pathway. BMPs have been identified in mammalian ovaries, and functional studies have shown that they are involved in the regulation of oogenesis and folliculogenesis. This review summarizes the role of the BMP system during formation, growth and maturation of ovarian follicles in mammals.

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This study aimed to investigate the effects of different concentrations of N-acetylcysteine (NAC) on the growth, antrum formation, viability, and ultrastructure of bovine secondary follicles cultured in vitro for 18 days. To this end, the follicles were cultured in TCM-199+ medium alone or supplemented with 1.0, 5.0, or 25.0 mM NAC. Follicular growth, antrum formation, viability (calcein-AM and ethidium homodimer-1) and ultrastructure were evaluated at the end of culture period. The results showed that 1.0 mM NAC increased the percentage of growing follicles and the fluorescence intensity for calcein-AM when compared to other treatments (p < 0.05). On the other hand, follicles cultured with 25.0 mM NAC had higher fluorescence intensity for ethidium homodimer-1, which is a sign of degeneration. Ultrastructural analysis showed that oocytes from follicles cultured in control medium alone or with 1 mM NAC had intact zonae pellucidae in close association with oolemmae, but the ooplasm showed mitochondria with a reduced number of cristae. On the other hand, oocytes from follicles cultured with 5 or 25 mM NAC had extremely vacuolated cytoplasm and no recognizable organelles. In conclusion, 1 mM NAC increases cytoplasmic calcein staining and the growth rate in bovine secondary follicles cultured in vitro, but the presence of 5 or 25 mM NAC causes damage in cellular membranes and organelles, as well as reducing the percentages of growing follicles.