Study of the molecular mechanism of progesterone and estradiol on the onset of puberty in Nellore heifers

• Grant number: 11/13852-0
• Support Opportunities: Regular Research Grants
• Start date: October 01, 2011
• End date: September 30, 2013
• Field of knowledge: Agronomical Sciences - Animal Husbandry - Animal Production
• Principal Investigator: Luis Felipe Prada e Silva
• Grantee: Luis Felipe Prada e Silva
• Host Institution: Faculdade de Medicina Veterinária e Zootecnia (FMVZ). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

The understanding of the molecular mechanisms by which nutrition, genetics and hormonal treatments affect the beginning of puberty is of great importance for developing strategies aiming to reduce the age at first calving, and therefore increase the slaughter rate in Nellore cattle. The effects of progesterone implant and of endogenous estradiol on the molecular mechanisms controlling the attainment of puberty in Nellore heifers will be investigated. 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 and the hypothalamus and ovaries will be removed for analysis. 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 next-generation sequencing (RNA-Seq), in order to identify possible candidate genes in the hypothalamus. The RNA-Seq results will be validated by qPCR quantification of 10 genes with differential expression. (AU)