Effect of leptin and nutrition on the expression profile of hypothalamic genes in zebu heifers (Bos taurus indicus

• Grant number: 09/08395-9
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: August 01, 2009
• End date: July 31, 2010
• Field of knowledge: Agronomical Sciences - Animal Husbandry - Animal Production
• Principal Investigator: Luis Felipe Prada e Silva
• Grantee: Rafael Araujo Ribeiro
• Host Institution: Faculdade de Medicina Veterinária e Zootecnia (FMVZ). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

The Nelore breed (Bos taurus indicus) compose the basis of Brazilian beef cattle herd. Nelore is well adapted to the tropical conditions, but it presents slow sexual maturation, what limits the slaughter rate of the herd. Thephysiological mechanism regulating the onset of puberty is not well understood, however several lines of research points to leptin as a main limitation of sexual maturity in undernourished heifers. The objective with this work isto identify hypothalamic genes whose expression is changed by leptin as well as by the energetic density of the diet, aiming to elucidate the mechanism of puberty regulation. Thirty two non pubertal zebu heifers, between 18to 20 months of age, will be divided into four experimental groups: low energy (LOW), high energy (HIGH), low energy with administration of recombinant bovine leptin (LOW+LEP), high energy with administration ofrecombinant bovine leptin (HIGH+LEP). After 40 days of experimental treatment, twenty four heifers will be selected, slaughtered and the hypothalamus will be collected. The heifers' condition of sexual maturity will bemonitored by ultrasound and by plasmatic progesterone concentration. The actual proposal limits itself to the extraction of hypothalamus and quantification of gene expression, since the feedlot phase, leptin administrationand determination of puberty will be realized in an already financed project (FAPESP 2006/03016-1). The effect of nutrition and leptin administration on the hypothalamic gene expression profile will be determined using DNAmicroarrays developed by a consortium of North American universities, containing 16,846 oligonucleotides for studies in bovine (http://www.bovineoligo.org/). The differential expression of 10 genes detected by microarrayhybridization, as well as the expression of five candidate genes, will be confirmed with real-time PCR. The elucidation of molecular mechanism regulating the zebu heifers' sexual precocity is necessary for the developmentof a therapeutic puberty induction protocol, or in more efficient genetic improvement programs to obtain earlymaturing zebu heifers.