Visualization and Identification of a Novel Sperm RNA Population

Abstract

Male infertility is an increasing, worldwide problem, which affects 8-12% of couples. Several factors cause male-related infertility, including genetic abnormalities, testicular trauma, and urogenital obstructions. However, in 30-50% of the male factor-related infertility cases, the cause is considered idiopathic, with no identifiable reason behind the infertility. Comprehensive knowledge of male germ cell production, maturation, and differentiation is fundamental to understanding the etiology of infertility. Male germ cells, spermatozoa, are produced via a conserved and highly controlled process called spermatogenesis, which occurs in the seminiferous tubules of the testes. Following the testicular development, sperm undergo crucial epididymal maturation. Properties acquired during spermatogenesis and epididymal transition are required for the sperm to be able to fertilize an oocyte. When entering the female reproductive tract, the sperm face several challenges before reaching the oviducts and the oocyte. Sperm needs to be able to swim through physical barriers in the cervix and in the utero-tubular junction, evade the immune system of the female reproductive tract, and form a sperm reservoir to prolong its lifespan. Before fertilization, sperm must undergo several changes in the FRT, including capacitation, hyperactivation, and acrosome reaction. Sperm RNA profile is unique and dynamic, consisting of several classes of non-coding RNA, such as microRNAs and piwi-interacting RNAs. However, there is still a lot to unravel regarding the sperm RNAs and their functional role in sperm survival, navigation through the female reproductive tract, and fertilization. The aim of this study was to gain novel insight into the sperm RNA repertoire in order to better understand the role of sperm RNAs in reproductive outcomes. Visualization of RNA molecules using specific RNA‑staining approaches revealed detailed cellular localization patterns of RNA within mouse spermatozoa. In addition, RNA sequencing was employed to molecularly characterize the sperm RNA population. Together, these results provide important new insights into the composition and organization of sperm RNAs, establishing a foundation for future research into male‑factor related infertility and for the development of RNA‑based diagnostic tools and improved infertility treatments.