MicroRNA-34 family expression in bovine gametes and preimplantation embryos

Abstract

BackgroundOocyte fertilization and successful embryo implantation are key events marking the onset of pregnancy. In sexually reproducing organisms, embryogenesis begins with the fusion of two haploid gametes, each of which has undergone progressive stages of maturation. In the final stages of oocyte maturation, minimal transcriptional activity is present and regulation of gene expression occurs primarily at the post-transcriptional level. MicroRNAs (miRNA) are potent effectors of post-transcriptional gene silencing and recent evidence demonstrates that the miR-34 family of miRNA are involved in both spermatogenesis and early events of embryogenesis.MethodsThe profile of miR-34 miRNAs has not been characterized in gametes or embryos of Bos taurus. We therefore used quantitative reverse transcription PCR (qRT-PCR) to examine this family of miRNAs: miR-34a, -34b and -34c as well as their precursors in bovine gametes and in vitro produced embryos. Oocytes were aspirated from antral follicles of bovine ovaries, and sperm cells were isolated from semen samples of 10 bulls with unknown fertility status. Immature and in vitro matured oocytes, as well as cleaved embryos, were collected in pools. Gametes, embryos and ovarian and testis tissues were purified for RNA.ResultsAll members of the miR-34 family are present in bovine spermatozoa, while only miR-34a and -34c are present in oocytes and cleaved (2-cell) embryos. Mir-34c demonstrates variation among different bulls and is consistently expressed throughout oocyte maturation and in the embryo. The primary transcript of the miR-34b/c bicistron is abundant in the testes and present in ovarian tissue but undetectable in oocytes and in mature spermatozoa.ConclusionsThe combination of these findings suggest that miR-34 miRNAs may be required in developing bovine gametes of both sexes, as well as in embryos, and that primary miR-34b/c processing takes place before the completion of gametogenesis. Individual variation in sperm miR-34 family abundance may offer potential as a biomarker of male bovine fertility.

Expression of miRNAs in Bull Spermatozoa Correlates with Fertility Rates

“…; Tscherner et al. ). These facts indicate that an aberrant expression in spermatozoa could have implications at least during early stages of pregnancy.…”

MicroRNAs and DNA methylation as epigenetic regulators of mitosis, meiosis and spermiogenesis

“…It has been demonstrated that all the members of miR-34 family (i.e. miR-34a, -34b and -34c) are found in bovine sperm (Tscherner et al 2014). Additionally, miR-34c seems to be important for the later steps of spermatogenesis because it is highly expressed in mouse pachytene spermatocytes and round spermatids in murine testis by targeting the activating transcription factor 1 (ATF1; Liang et al 2012).…”

Spermatozoa micro ribonucleic acid–34c level is correlated with intracytoplasmic sperm injection outcomes

“…In several species, miR-34 may be involved in early embryonic development (4,15,16), and sperm-borne miR-34c has been reported to be important for the first cleavage division of mouse embryo, via the modulation of B-cell lymphoma-2 expression (15). However, the impact of spermatozoa miR34b/c on human embryonic development has not been explored.…”

“…However, the paternal contribution to the zygote increasingly is being recognized. Several transcripts that are present in human spermatozoa and zygotes are absent in unfertilized oocytes, suggesting that spermatozoa deliver these transcripts to oocytes during fertilization, and that they may play a role in subsequent zygote and embryonic development (3 (4).…”

“…The miRNAs in this family have been recognized to be tumor suppressors because they are direct targets of the tumor suppressor gene p53 (12). Although miR-34a is ubiquitously expressed in humans, miR-34b/c is detected in a small subset of tissues, particularly the gonads (4,12).…”