The Sperm Small RNA Transcriptome: Implications beyond Reproductive Disorder.

Apart from the paternal half of the genetic material, the male gamete carries assorted epigenetic marks for optimal fertilization and the developmental trajectory for the early embryo. Recent works showed dynamic changes in small noncoding RNA (sncRNA) in spermatozoa as they transit through the testicular environment to the epididymal segments. Studies demonstrated the changes to be mediated by epididymosomes during the transit through the adluminal duct in the epididymis, and the changes in sperm sncRNA content stemmed from environmental insults significantly altering the early embryo development and predisposing the offspring to metabolic disorders. Here, we review the current knowledge on the establishment of the sperm sncRNA transcriptome and their role in male-factor infertility, evidence of altered offspring health in response to the paternal life experiences through sperm sncRNA species and, finally, their implications in assisted reproductive technology in terms of epigenetic inheritance.

The repertoire of testicular extracellular vesicle cargoes and their involvement in inter-compartmental communication associated with spermatogenesis.

BACKGROUND: Spermatogenesis is regulated by a complex network of intercellular communication processes. Extracellular vesicles (EVs) are one of the important mediators in intercellular communication. Previous reports have demonstrated the involvement of EVs from the epididymis and prostate in sperm maturation and function. However, the presence of EVs in the testis and their potential involvement in spermatogenesis has not been explored. Here, we have established a testis dissociation protocol that allows the isolation and characterization of testicular EVs. RESULTS: We show that testicular EVs are specifically and efficiently taken up by somatic cells and germ cells, including the spermatozoa in the interstitial space and the seminiferous tubule compartments. We profiled the proteome of testicular EVs and probed the cell types that release them, revealing the potential contributions from the Leydig cells and testicular macrophages. Moreover, we sequenced the small RNA cargoes of testicular EVs and identified sets of small non-coding RNAs that were overlooked in the testis transcriptome. Selected miRNA candidates in testicular EVs were found in sperm RNA payload and demonstrated specific resistance towards ribonuclease A independent of the vesicle membrane. Small molecule inhibition of EV secretion perturbed spermatogenesis via inter-compartmental communication. CONCLUSIONS: Together, our study provides a valuable resource on the repertoire of cargoes carried by testicular EVs and uncovers a physiological function of testicular EVs in inter-compartmental communication associated to spermatogenesis.

Hippo kinases MST1 and MST2 control the differentiation of the epididymal initial segment via the MEK-ERK pathway.

Although the roles of the Hippo pathway in organogenesis and tumorigenesis have been well studied in multiple organs, its role in sperm maturation and male fertility has not been investigated. The initial segment (IS) of the epididymis plays a critical role in sperm maturation. IS differentiation is governed by ERK1/2, but the mechanisms of ERK1/2 activation in IS are not fully understood. Here we show that double knockout (dKO) of mammalian sterile 20-like kinases 1 and 2 (Mst1 and Mst2), homologs of Hippo in Drosophila, in the epididymal epithelium led to male infertility in mice. Sperm in the cauda epididymides of mutant mice were immotile with flagellar angulation and severely disorganized structures. Loss of Mst1/2 activated YAP and increased proliferation and cell death in all the segments of epididymis. The mutant mice showed substantially suppressed MEK/ERK signaling in the IS and failed IS differentiation. Deletion of Yap restored the reduced MEK/ERK signaling, and partially rescued the defective IS differentiation and fertility in Mst1/2 dKO mice. Our results demonstrate that YAP inhibits the MEK/ERK pathway in IS epithelial cells, and MST1/2 control IS differentiation and fertility at least partially by repressing YAP. Taken together, the Hippo pathway is essential for sperm maturation and male fertility.