Desenvolvimento in vitro de embriões bovinos expostos ao choque térmico e ao Fator Estimulador de Colônia 2

Abstract

The interaction between the embryos and the surrounding environment can modulate embryo development, affecting its competency to develop into blastocyst and to establish a gestation. The endometrium secretes embryocines responsible to promote embryo development while the increase in mother body temperature disrupt the embryo viability. This thesis aimed to evaluate alterations in embryos exposed to the embryokine Colony Stimulator Factor 2 (CSF2), secreted in the uterus environment and related to modulate embryo development, as well heat stress, that induce cellular stress in developing embryos. Due to the effect of increasing body core temperature on dairy cows conception rate, we also evaluated the vaginal temperature variation in Girolando cows on summer. On chapter one, we evaluated the vaginal temperature variation of three different genetic groups of Girolando under pasture during the summer. The vaginal temperature had estimated linear increase of 0.05 degrees of each temperature humidity index unit increase (P<0.001). Cows with 1/2 of Holstein genetic on crossbred composition (H) had smaller vaginal temperature variation over 24h than cows with 3/4 and 7/8 H (P<0.001). We conclude that the trophoctoderm of blastocysts may goes to epigenetic modifications by embryo sex and bull inheritance through alterations in histone epigenetic marks. Heat shock between days 2.5 to 3 of in vitro culture do not affect embryo development, but reduce the embryo quality. The proportion of Holstein genetic on Girolando cows higher than 3/4 reduces cow resistance to heat stress. In the second chapter, we evaluated the effect of CSF2 on embryo development competence and quality previously stressed by heat shock between days 2.5 to 3 of embryo in vitro culture. There were no effect of heat shock and CSF2 on embryo development and number of embryo cells. Although, heat stressed embryos had lower number and index of TUNEL-positive cells on trophoctoderm (P=0.0270 e P=0.0240) and total embryo (P=0.0029 e P=0.0031), and showed reduced mitochondrial activity (P=0.0073). The CSF2 did not affected any embryo quality evaluated variables. In the third chapter we evaluated the effect of CSF2, sex of embryos and sire used in fertilization on the embryo development competence and post-translational modifications to Histone 3 in blastocyst trophoctoderm. It was found that amounts of immunolabeled H3K27me3 were greater (P=0.030) for male embryos than female embryos. Additionally, labeling for H3K27me3 and H3K18ac depended upon the bull from which embryos were derived. Although CSF2 reduced the proportion of embryos developing to the blastocyst, there was no effect of CSF2 on labeling for H3K27me3 or H3K18ac.