Mitochondrial signals mediate paternal effects on offspring metabolism (Smart-Seq)
Spermatozoa deliver a complex and environment sensitive pool of small non-coding RNAs (sncRNA) to the oocyte at fertilisation [ref], which influences offspring development and adult phenotypic trajectories [refs]. Whether mature spermatozoa in the epididymis can directly sense the environment is still not fully understood [ref]. Here, we used two distinct paradigms of preconception acute High Fat Diet challenge to dissect epididymal vs spermatogenic contributions to the sperm sncRNA pool and offspring health. We show that epididymal spermatozoa, but not developing germ cells, are sensitive to the environment and identify mitochondrial tRNA fragments as sperm-born sensors. In human spermatozoa, we found mt-tsRNAs in linear association with BMI and showed that paternal overweight at conception is sufficient to double offspring obesity risk and compromise metabolic health. Using mouse genetics and metabolic phenotypic data, we show that alterations of mt-tsRNAs are downstream of mitochondrial dysfunction in mice. Most importantly, single embryo transcriptomics of genetically hybrid two-cell embryos demonstrated  sperm-to-oocyte transfer of mt-tsRNAs at fertilisation and implied them in the control of early embryo metabolism.  Our study supports the importance of paternal health at conception for offspring metabolism, propose mt-tsRNAs as sperm-born environmental effectors of paternal inheritance and demonstrate, for the first time in a physiological and unperturbed setting, father-to-offspring transfer of sperm mt-tsRNAs at fertilisation. Overall design: Oocytes from C57BL/6N-mtST were fertilized with sperm from HFD or LFD treated C57BL/6N animals. Early 2cell embryos were collecetd after overnight incubation and snap frozen in lysis buffer according to SMARTseq2 protocol.