Validation_of_higher_mutation_rates_in_early_embryonic_mutations_in_the_paternal_germlime_in_laboratory_mice. Validation_of_higher_mutation_rates_in_early_embryonic_mutations_in_the_paternal_germlime_in_laboratory_mice

This proposed study is to replicate an intriguing finding from our previous experiment to sequence multi-sibling mouse pedigrees. We previously generated a high quality set of denovo mutations by whole genome sequencing of 10 offspring and both parents each from two large mouse pedigrees, chosen from a large cross breeding experiment (n=20 pedigrees). We then genotyped the mutations across all offspring in both pedigrees (n=57/77), and three tissues from each of the parents. We observed 17 mutations that had occured as early embryonic mutations in the parents, manifesting themselves as mutations with very low alternate allele frequencies across tissues in the parents (~1-9%), and as denovo mutations shared across a proportion of the offspring. 16/17 of these mutations arose on the paternal germline, with only one attributable to the maternal germline. We also observed an additional 53 mutations shared between offspring, but not as parental mosaics. No paternal bias is evident in these later parental embryonic mutations. These findings suggest a marked sex difference in germline mutation processes in the first ~10 cell divisions post-fertilisation, at a time when there is no overt sexual differentiation, prior even to the specification of primordial germ cells. Two potential explanations are: (i) the germline and somatic lineages split much earlier in female mice, and/or (ii) the mutation rate per cell division is much higher in male mice. This finding is ultimately based only on two mating pairs. We would like to carry out an additional experiment to validate the paternal bias in mutation rates that we see in early embryonic stages. This will involve WGS and validation of denovo mutations from 28 individuals from the remaining unsampled pedigrees, representing 5 offspring and both parents from 4 additional breeding pairs.