The understanding of molecular mechanisms by which nutrition, genetics and hormonal treatments affect the initiation of puberty is of great importance for developing strategies for reducing age at first calving, and therefore slaughter rate in Nellore cattle. We will investigate the effects of progesterone implant and of endogenous estradiol on molecular mechanisms controlling the attainment of puberty in Nellore heifers. Specifically, the molecular pathways of leptin, estradiol and NPY signaling will be studied in the hypothalamus, and the IGF-I, GH and LH pathways will be studied in the ovary. Thirty six non-pubertal heifers, between 13 and 14 months of age, will be divided into four groups (nine per group): P4 implant without estradiol (P-E), P4 implant with estradiol (P+E), without P4 implant and without estradiol (E-), and without P4 implant and with estradiol (E+). The heifers will be kept under grazing, with access to mineral supply and water. At the end of the hormonal treatments all heifers will be slaughtered. The hypothalamus and other tissues, except the ovary, will be collected and stored at -80°C. The granulosa cells will be isolated from the ovaries and then also stored at -80°C. Total RNA will be extracted, treated with DNase I and submitted to cDNA synthesis for gene expression quantification by real time PCR (qPCR). A total of fourteen candidate genes will be quantified by qPCR. A comprehensive study of the effects of progesterone administration and endogenous estrogen on attainment of puberty will also be conducted through DNA microarrays hybridization, in order to identify possible candidate genes in the hypothalamus. The microarray results will be validated by qPCR quantification of 10 genes with differential expression.
News published in Agência FAPESP Newsletter about the scholarship: