Sperm RNA: Quo vadis?

Various different classes of RNAs contained in sperm cells have emerged as causal vectors for the transmission of acquired information from father to offspring. This has invigorated research and raised many new questions concerning the heritability of disease risk and the ability to adapt to novel environments. Here, we will focus on recent advances in the field of epigenetic germline inheritance in mammals, with a particular focus on the following three questions: (1) What is the current evidence for an involvement of sperm RNAs in the transmission of acquired information from father to offspring? (2) How can acquired changes in the sperm-RNA payload be induced in the male germline? (3) How can acquired changes be transferred from sperm to oocyte? We propose a novel mechanism for transfer of sperm RNA to the oocyte in a DNA/RNA-hybrid, possibly interacting with DNA-bound proteins, and suggest experiments that should advance our understanding of epigenetic germline inheritance.