Epigenetic Inheritance of Paternal Environmental Conditions

Several studies show that parental nutrient availability can affect metabolic phenotypes in the offspring. However, the mechanisms by which parental conditions influence offspring remain poorly understood. Previously we found that mice fed on low protein diet sire offspring with altered lipid and cholesterol metabolism. My recent work showed that small RNA in sperm, specifically tRNA-derived fragments (tRFs), play roles in the inheritance of paternal dietary information. Protein restriction in mice affects small RNA levels in mature sperm, with decreased let-7 levels and increased amounts of 5′ fragments of glycine transfer RNAs. These studies also revealed surprising dynamic aspects of small RNA biogenesis during sperm maturation; tRFs are scarce in testicular sperm but increase in abundance as sperm mature in the epididymis. To further examine the mechanism of this RNA-mediated epigenetic inheritance, this project aims to address two broad questions 1) how are sperm small RNAs generated in response to low protein diet 2) what is the effect of sperm RNA on early embryonic development? To address the first question, here I propose to first definitively identifying the tissue of origin of tRFs in sperm (Aim1). I will use three distinct methods for generating “tracer” RNAs specifically in a tissue of interest to uncover the tissue of origin for tRFs. Secondly, my data shows that the small RNA payload of sperm changes during epididymal maturation. This has important implications for assisted reproduction in humans, which in some cases utilizes relatively immature sperm from testicular biopsies, for example, to fertilize oocytes. It is therefore of biomedical interest to investigate the function of sperm small RNAs in embryonic development. Here I propose to generate embryos using a variety of combinations of sperm and exogenous RNAs and characterize regulatory consequences in early development, and later phenotypic consequences in offspring carried to term (Aim 2).