Ocorrência de splicing alternativo e polimorfismos de base única na sequência do receptor de hormônio luteinizante e relação com o desenvolvimento folicular em Bovinos Leiteiros

Abstract

The aim of this study was to evaluate genomic and transcriptomic variations at the luteinizing hormone receptor (LHR) and its role at the follicular dominance establishment and superovulation outcome in bovine. Three experiments were performed, and for all evaluations cDNA synthesized from total RNA extracted from follicular granulosa cells (GC) were used. To characterize the LHR transcript, GC were recovered from dominant follicles from Gir (n=16) and Holstein (n=16) cows. After PCR and sequencing, data were analized to identify polymorphisms, allelic frequency, polymorphic information content (PIC) and Hardy-Weinberg Equilibrium (HWE). Twenty one single nucleotide polymorphism (SNP) were identified, being 17 in Gir and 14 in Holstein. The classification of SNP according to PIC values identified 12 as highly informative in Gir and five in Holstein. Considering HWE, eight SNP were not in equilibrium in Gir and 10 in Holstein. Two isoforms were also identified, one in exon 1 and other in exon 10. We concluded that LHR in dairy cattle shows a high frequency of polymorphism and multiple isoforms. To evaluate the LHR isoforms role in GC during follicular divergence, the follicular wave emergence was synchronized in Gir (n=10) and Holstein (n=10) heifers and follicles were individually aspirated at the corresponding sizes of pre-, divergence, and post-. The relative expression of LHR isoforms was determined by real time PCR and results were correlated to the intrafollicular estradiol (E2if) concentrations. In both breeds, there was a progressive increase in E2if concentration during follicular development. The E2if in Holstein was higher when compared to Gir before, during, and after divergence; but was similar in follicles of same size in both breeds. We observed a peak for the total LHR expression after the beginning of the follicular divergence. The expression of LHR isoforms was low (Holstein) or under-regulated (Gir) during this same period. The results suggest that the early follicular divergence of the dominat follicle in Bos indicus breeds can be related to a higher sensitivity to the estradiol negative feedback. Besides, sequential changes in LHR isoforms expression can act regulating the LHR function during folicullar divergence in bovine. The evaluation of LHR isoforms behavior during the exogenous induction of follcilualr development was performed in Gir heifer previously characterized as good (n=5) or poor (n=5) responders to superovulation. In both groups, GC were collected from follicles (8 mm) which growth occurred without (Control) or with FSH stimulation (SOV). In good responders group, there was no difference in the LHR expression between the Control and SOV treatments. In the poor responders group, the total LHR expression was lower in SOV when compared to Control, but there was no difference in the expression of the isoforms. We concluded that LHR is differentially expressed in dominant follicles from heifers characterized as good or poor responders to superovulation.