The role of extracellular vesicles in soma-to-germline communication

The inheritance of environmentally-induced traits is an established phenomenon, however the underlying molecular mechanism is yet to be elucidated. In some cases, environmental factors may act directly on the germline, however in other cases this appears impossible. While ‘soma-to-germline feedback’ conflicts with the long-held dogma that heritable genetic information flows solely from germline to soma, there is no reason to suppose that germline- associated somatic cells cannot communicate with developing germ cells. A prime candidate for the means of such communication is small RNAs carried within extracellular vesicles (EVs). Small RNAs have been associated with inheritance of acquired phenotypes across phyla, and EVs are known intercellular messengers produced by nearly all cells. In this thesis, I have taken the first steps towards testing this idea by investigating the hypotheses that EVs produced by germline-associated somatic cells transfer small RNA cargo to germ cells, and that the RNA cargo is susceptible to environmental influence. I isolated and characterised EVs from two types of germline-associated somatic cells, Sertoli cells (in vitro) and epididymal epithelial cells (in vitro and in vivo), and characterised their small RNA profiles using high-throughput sequencing. By co-incubating labelled Sertoli EVs with spermatogonial stem cells (SSCs) and labelled epididymal EVs with living sperm, I showed that these EVs interact with germ cells. Furthermore, I also demonstrated the transfer of many Sertoli EV small RNAs to SSCs. I also established that the small RNA profiles of EVs can be influenced by the environment. I used Bisphenol A and dimethyl sulfoxide as environmental stressors of Sertoli cells, varied the concentration of folate available for in vitro epididymal cells, and modelled the response of in vivo epididymal EVs to dietary methyl donor supplementation. The small RNAs affected by these factors included miRNAs associated with transcription and nucleic acid-binding (some of which were transferred from Sertoli EVs to SSCs), and tRNA-derived fragments that have previously been associated with the vertical transmission of diet-induced phenotypes. Taken together, my data show that small RNA cargo from somatic EVs is susceptible to environmental influence, and thus such somatic RNA is capable of being transferred to the germline