Sperm RNAs delivered to the zygote during fertilization have emerged as important non-genetic contributors to embryo development and offspring health. Interestingly, small RNAs are delivered to sperm during post-testicular maturation in the epididymis. Moreover, this developmental window is vulnerable to environmental stressors, leading to a reprogramming of the sperm RNA code, with significant post fertilisation consequences. Despite this knowledge, there remains limited understanding of the specific RNAs delivered to sperm during epididymal transit or how paternal exposures influence the remodelling of the sperm RNA landscape.
Focusing on a subclass of small RNAs, microRNAs (miRNAs), we utilised Cre:lox conditional genetics to selectively ablate Dgcr8, a key protein involved in miRNA biogenesis, in the epididymal epithelium to investigate the function of sperm miRNAs in the embryo. Small RNA sequencing of populations of sperm revealed reduced abundance (~5-fold decrease) of 27 miRNAs. Moreover, embryos fertilized by sperm from these mice displayed significantly increased expression of 184 genes (P < 0.01). Remarkably, however 65% of these gene changes were rescued when embryos were supplemented with purified epididymal miRNAs, linking reduced sperm miRNA levels with transcriptomic dysregulation in the early embryo. Further, we have established that the epididymis mounts a response to multiple different paternal environmental exposures, leading to an altered sperm RNA profile. Indeed, exposure to increased ambient temperature led to the accumulation of RNA changes in sperm from exposed mice that are causally linked to accelerated embryo development, changes in embryonic gene expression and increased fetal:placental weight ratio. Ultimately, this work aims to deepen our understanding of the establishment and modulation of the sperm RNA profile and its subsequent post fertilisation consequences.