lteration of chromatin-modifying enzymes expression in pre-ovulatory follicles in adult cows gestated under high temperature- humidity index.

Abstract

In cattle, gonadal development and gametogenesis occur during gestation. When dairy cows suffer high temperature and humidity conditions at pregnancy, the fertility of their offspring can be compromised. This could be consequence of variations in expression of proteins involved in follicular growth and development, which are regulated by different enzymes acting on chromatin structure, such methylating DNA enzymes. The aim of the study was to analyze the expression of DNA Methyltransferases (DNMTs) in preovulatory follicles of cows gestated under different environmental conditions. Adult Argentinean Holstein cows (n=24) gestated under different THI conditions during their in utero development were used. Ovarian samples were obtained by ovariectomy after estrous synchronization and gene and protein expression of DNMTs (DNMT1, DNMT3a and DNMT3b) was determined by RT-PCR and immunohistochemistry in pre-ovulatory follicle. Gestation was divided into two periods (P1: 0-150 days; P2: 151 days-birth); and three trimesters (T1: 0-90 days; T2: 91-180 days; T3: 181-birth days) in which the exposure to high Temperature-Humidity Index (THI) was considered. Negative associations between gene expression of DNMTs and THI during all gestation and particularly in the second trimester were observed. Also, negative associations between DNMT1, DNMT3a protein expression in granulosa cells of preovulatory follicles and THI in T3 and P2 were observed. Instead, positive associations between DNMT3a in granulosa cells and THI in T1 were detected. Besides, DNMT3b expression in theca interna were positively associated to high THI during all gestation. This data suggests that exposure to high THI during intrauterine development influences the expression of genes and proteins associated with epigenetic modifications and may affect the expression of molecules critical for the development and function of pre-ovulatory follicles in adultlife.