Epididymal acquired sperm microRNAs modify post-fertilization embryonic gene expression

Sperm small RNAs have emerged as important non-genetic contributors to embryogenesis and offspring health. A subset of sperm small RNAs are thought to be acquired during epididymal transit. However, the transfer of RNAs from the somatic epididymis to sperm has been questioned, and the identity of the specific small RNAs transferred remains unclear. Here, we employ Cre/Lox genetics to generate germline- and epididymal-specific Dgcr8 conditional knockout mice to investigate the dynamics of sperm microRNAs and their function in the early embryo. Testicular sperm from germline specific Dgcr8 knockout mice have reduced levels of 98 microRNAs. Enthrallingly, following epididymal transit the abundance of 59% of these microRNAs are restored to control levels. Conversely, sperm from epididymal Dgcr8 knockouts displayed a reduction of > 3.4-fold in 25 miRNAs. This substantial loss of epididymal miRNAs in sperm was accompanied by transcriptomic changes in the embryo which was rescued by microinjection of epididymal miRNAs. These findings ultimately demonstrate the acquisition of miRNAs from the soma by sperm during epididymal transit and their subsequent regulation of post-fertilization embryonic gene expression.