Expression of microRNA in male reproductive tissues and their role in male fertility

MicroRNA (miRNA) are small non-coding RNA, approximately 22 nucleotides in length, that regulate gene expression through their ability to bind to mRNA. The role of miRNA in cellular and tissue development is well documented and their importance in male reproductive tissue development is actively being evaluated. They are present in spermatogonia, Sertoli and Leydig cells within the testis and are present in mature spermatozoa, indicating roles in normal testicular development, function and spermatogenesis. Their presence in spermatozoa has led to postulations about the roles of male miRNA during early embryonic development after fertilisation, including chromatin restructuring and possible epigenetic effects on embryo development. MiRNAs are also present in body fluids, such as blood serum, milk, ovarian follicular fluid and seminal fluid. Circulating miRNAs are stable, and aberrant expression of cellular or extracellular miRNA has been associated with multiple pathophysiological conditions, the most studied being numerous forms of cancer. Considering that miRNAs are present in spermatozoa and in seminal fluid, their stability and the relatively non-invasive procedures required to obtain these samples make miRNAs excellent candidates for use as biomarkers of male reproduction and fertility. Biomarkers, such as miRNAs, identifying fertile males would be of financial interest to the animal production industry.

Effect of stallion age on the expression of LH and FSH receptors and aromatase P450 in equine male reproductive tissues

The aim of the present study was to characterise receptors for LH and FSH (LHR and FSHR, respectively) and aromatase in epididymal and testicular tissue from stallions of different ages (prepubertal, young, mature and old). Gene and protein expression were assessed by real-time quantitative polymerase chain reaction (real-time qPCR), immunohistochemistry and multiple immunofluorescence labelling. There were no differences in LHR mRNA expression in epididymal and testicular parenchyma in stallions of different age. In contrast, expression of FSHR and CYP19A1 in caput, corpus and cauda epididymis and in testicular parenchyma increased with age (P < 0.001). Immunolabelling for LHR, FSHR and aromatase was influenced by puberty. In postpubertal stallions, positive staining for LHR and aromatase was detected in Leydig cells, whereas protein expression of FSHR was present in Sertoli cells and primary spermatocytes. In prepubertal colts, staining for LHR, FSHR and aromatase was detected in seminiferous tubules. In epididymal tissue, aromatase was present in the cauda epididymis only, regardless of age. In conclusion, the results highlight the significance of gonadotropin action and oestrogen production for the maturation of male reproductive tissue in the horse. The presence of FSHR in the seminiferous tubules suggests effects of FSH on spermatogenesis in this species. The importance of oestrogen production for maintenance of testicular function in stallions was confirmed.