Micro-RNAs espermáticos relacionados à fertilização e ao desenvolvimento embrionário inicial in vitro de bovinos (Bos taurus)

Abstract

Epigenetics is defined as the study of heritable alterations in gene expression without changing the primary DNA sequence. The so-called “epigenetic factors” act on gene expression by regulating cellular phenotypic characteristics. MicroRNAs (miRNAs) comprise a class of epigenetic factors that are small endogenous RNA molecules unable to encode proteins and that act in pre or post-transcriptional regulation of gene expression, degrading or blocking messenger RNAs. However, we do not yet fully understand the functions of these sperm RNAs in fertilization and embryonic development. The present study aimed to evaluate the sperm content of miRNAs in bulls and correlate it with the process of fertilization and early embryonic development. Semen samples from eight crossbred bulls (Bos taurus x Bos indicus) were used in in vitro embryo production (PIVE) routines and for semiquantitative evaluation of sperm miRNA content. To identify possible correlations between miRNA content with the fertilization process and early embryonic development, Pearson's correlation test was performed between the percentage amount of each miRNA type and the cleavage and blastocyst rates obtained in PIVEs, respectively. Among the 336 types of miRNAs found in at least one of the samples, MiRNA bta-miR-425-5p showed significant positive correlation with blastocyst rate. Thus, these miRNAs may be directly or indirectly regulating the expression of genes important for early development, or they may be just residues of proper spermatogenesis. In any case, these miRNAs have potential as molecular markers of fertility, as proper embryonic development is essential for term gestation, that is, essential for good fertility. Finally, miRNAs bta-miR-1246, bta-miR-11975, bta-miR-2285bf , bta-miR-335 and bta-miR-7 showed a significant negative correlation with blastocyst rate, which can be interpreted as miRNA acting directly or indirectly in the expression of genes important for early embryonic development, or just as residues of inadequate spermatogenesis. However, it has potential as a molecular marker of fertility problems in bulls.