Micro-RNAs differentially expressed in comparative analysis of sperm samples with high and low efficiency in the in vitro production of bovine (bos taurus) embryos

Abstract

Infertility or subfertility in bovine males may be related to spermatic microRNAs (miRNAs), whose function seems to be associated with the regulation of gene expression, degradation or storage of messenger RNAs (mRNAs) for later translation into early embryonic development. Thus, the purpose of this study was to identify differentially expressed miRNAs in semen samples from bulls (Bos taurus) with low and high efficiency in the in vitro embryo production (IVEP) and to evaluate if they can be used as markers of semen efficiency for IVEPs. In order to identify miRNA markers of semen efficiency in the in vitro embryo production, eight semen samples from each animal, one bull with high and two bulls with low efficiency in IVEPs were used to perform the RNAseq technique for miRNAs. Initially the samples were washed with PBS to remove the extender semen and subsequently were submitted to RNA extraction protocols performed according to procedures described by mirVana TM miRNA Isolation Kit. Then, the amplification of the miRNAs was carried out, not to mention the preparation of the library (Ion Total RNA-Seq Kit v2), the PCR emulsion reaction, enrichment, as well as the injection of the sample on the chip by the Ion Chef equipment. The sequencing was done on Ion Proton equipment. The comparison between the samples was established using two methodologies for searching for targets to increase the robustness of the analytical procedure: the miRanda program using as cutoff minimum free energy of the hybridization -20 kcal/Mol, 100% of identity between nucleotides 2 and 8 of the miRNA, and the RNAhybrid program, using as cutoff minimum free energy of hybridization -20 kcal/mol. In sum, 1306 miRNAs were identified in the samples. The bta-miR- 380-5p, bta-miR-155, bta-miR-30c and bta-miR-34a genes were identified by the Bioinformatics as being strongly differentially expressed between the groups, indicating that these genes may present themselves as possible efficiency markers. However, it has become clear that there is no single miRNA that marks different types and causes of fertility problems.