Reduction in maternal Polycomb levels contributes to transgenerational inheritance of a response to toxic stress in flies

Transgenerational persistence of parental responses to environmental stimuli has been reported in various organisms, but the underlying mechanisms remain underexplored. In one of these reported examples, we have shown that exposure of fly larvae to G418 antibiotic leads to non-Mendelian inheritance of ectopic induction of certain developmental genes. Here we investigate if this inheritance involves changes in mRNA composition within the early, maternal-stage offspring embryos of exposed flies. Exposure to G418 in F1 modified the maternal RNA levels of many genes in their early (F2) embryos. This includes reduction of maternal Polycomb group genes which persisted in the following generation of embryos (F3). To investigate the functional meaning of this reduction, we compared genetically normal embryos of Polycomb mutant females to normal embryos of normal females. Analysis with two different alleles of Polycomb, Pc1 and Pc3, revealed that maternal reduction in Polycomb gene dosage has a positive influence on the inheritance of induced expression. Together, this shows that exposure to G418 stress reduces the maternal levels of Polycomb in the offspring embryos and this reduction contributes to the inheritance of induced expression.