Abstract
Semen fertilizing potential is dependent upon the morphological, functional and molecular attributes of sperm. Sperm microRNAs (miRNAs) were recently shown to hold promise regarding their association with different fertility phenotypes. However, their role in fertility regulation remains to be determined. We postulated that sperm miRNAs might regulate early embryonic development. From this perspective, sperm quality and 380 sperm miRNAs were investigated in frozen–thawed semen from high (HF; 54.3 ± 1.0% pregnancy rate) and low (LF; 41.5 ± 2.3%) fertility bulls. Out of nine miRNAs that showed different levels in sperm cells, miR-216b was present at lower levels in HF sperm cells and zygotes. Among miR-216b target genes (K-RAS, BECN1 and JUN), K-RAS, related to cell proliferation, revealed a higher level in HF two-cell embryos. First cleavage rate, blastocyst cell number and division number were also higher in HF. In addition, by using a model based on polyspermy embryos, we demonstrated an increase in miR-216b levels in zygotes associated with sperm cell entry. Our results shed light on a possible mechanism of paternal contribution involving sperm-borne miR-216b that modulates levels of miR-216b in zygotes and K-RAS in two-cell embryos. This modulation might regulate early development by interfering with the first cleavage and blastocyst quality.
Highlights
Semen fertilizing potential is dependent upon the morphological, functional and molecular attributes of sperm
One strand binds to a complex of Argonaute proteins to form the RISC complex (RNA-induced silencing complex) whose activity is dependent on binding of the miRNA to the 3′ untranslated region (3′ UTR) of its target gene: perfect binding induces degradation of the target mRNA; while imperfect binding prevents translation of the target mRNA11
Experiment 1: Lower level of miR-216b in sperm cells and zygotes is associated with a high level of K-RAS in two-cell embryos and an increase in first cleavage rate and blastocyst cell number
Summary
Semen fertilizing potential is dependent upon the morphological, functional and molecular attributes of sperm. Our results shed light on a possible mechanism of paternal contribution involving sperm-borne miR-216b that modulates levels of miR-216b in zygotes and K-RAS in two-cell embryos This modulation might regulate early development by interfering with the first cleavage and blastocyst quality. Molecular sperm signatures are frequently linked to their contribution to early embryonic development, which involves delivery of the following to the embryo: sperm DNA, mRNAs, proteins and non-coding RNAs such as microRNAs (miRNAs) that appear to be related to healthy sperm and male fertility potential[2,9,10]. Based on (1) the dependence on morphological, functional and molecular sperm attributes for male fertility success, and, (2) the potential of sperm-borne miRNAs to play a role in fertility by regulating embryo development, we hypothesized that initial steps of embryo development are under the control of specific miRNAs delivered by sperm cells. The aims of this study were to: (1) determine the SQA and miRNA profiles of semen samples from high and low fertility bulls; (2) investigate the relative levels of sperm miRNAs and target genes in embryos from high and low fertility sperm samples; (3) investigate how alterations in miRNAs could regulate embryo development; and (4) demonstrate that sperm cells are capable of delivering miRNAs to the zygote
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