Abstract

Control of postnatal testis development before puberty and maintenance of adult testis spermatogenesis function involves the coordinated actions of genetic, molecular, and endocrine, factors. The net result of these factors is the continual proliferation and differentiation of testes spermatogonia during the establishment and maintenance of spermatogenesis. Studies in mice reveal that complex gene networks are involved in spermatogonia proliferation and differentiation during normal spermatogenesis. These studies have led to advances in vitro and in vivo manipulation of spermatogonia in mice. Recently, the role of small non-coding RNA species has come to the forefront in the regulation or fine-tuning of gene expression in the testes. Small non-coding RNAs microRNA (miRNA) are present in spermatozoa, testes, and epididymis and thus underscore the complex transcriptional control and cell-cell communication required for spermatogenesis, and sperm transport and function. Human, goat, and pig testes express miRNAs, and in humans, the miRNAs expression profile is dependent on the clinical status of spermatogenesis. The molecular roles of miRNAs are unknown but are likely important during the establishment and maintenance of spermatogenesis. The gene networks and molecular mechanisms controlling the continual proliferation and differentiation of spermatogonia in the pre-meiotic and post-meiotic goat testes are mostly unexplained. There is a need to characterize these gene networks to provide insight into the (1) in vivo mechanisms controlling continual spermatogonia proliferation and differentiation, (2) factors necessary for identification, isolation and subsequent in vitro manipulation of spermatogonia, (3) development of molecular markers for the potential fertility of individual animals and (4) identification of therapeutic, reversible targets for male contraceptives. Therefore the objectives of the current study were to (1) identify gene networks important to establish spermatogenesis function of the testes using mRNA- and miRNA-sequencing, (2) corroborate the temporal and spatial expression of candidate gene networks by qPCR and (3) immunohistochemistry.

We observed an enrichment of genes or gene networks involved in the lysosome, endocytosis, apoptosis, cell junctions, focal adhesions, protein digestion and absorption amongst others. Interestingly the protein digestion and absorption pathway identified in juvenile goat testes our RNA sequencing experiments are best described for its role in the intestinal epithelium during protein digestion. Not only does it involve the transport of small peptides and amino acids but also the metabolism of non-digestible peptides and proteins by commensal bacteria. Since we had identified a testis microbiome, we decided to look closer at the protein digestion and absorption pathway by IHC. To date, we demonstrated that the temporal and spatial expression of SLC16A10, SLC15A1, and SLC7A8, solute carrier proteins involved in the transport of small peptides and amino acids across the plasma membrane, decrease from 2-month to 4-month testes. RNA sequencing experiments showed a similar temporal pattern. Spatially, the expression was confined to cells within or immediately surrounding the seminiferous tubules. We are continuing to define the difference in pre-meiotic and meiotic goat testes, and that also may be essential to maintain spermatogenesis in post-pubertal testes.

Speaker

Dr. Lewis, Research Scientist in the Animal Systems group in the Cooperative Agricultural Research Center and International Goat Research Center, is a reproductive physiologist and molecular biologist. He trained in the molecular, endocrine, and cellular fetal/maternal interactions during implantation at Texas A&M University and the genetic basis for male genitourinary birth defects at Baylor College of Medicine. He has been at PVAMU since 2013.