Oocyte mitochondria link maternal environment to offspring phenotype in C. elegans

Oocytes undergo a recently discovered mitochondrial proteome remodeling event in flies1, frogs1, and humans2. This oocyte mitochondrial remodeling event, which includes substantial changes in electron transport chain (ETC) subunit abundance1,2, is regulated by maternal insulin signaling1. However, why oocytes undergo mitochondrial remodeling is unknown, with some speculating that it might be a conserved mechanism to protect oocytes from genotoxic damage by reactive oxygen species (ROS)2. In Caenorhabditis elegans, we previously found that maternal exposure to osmotic stress drives a 50-fold increase in offspring survival in response to future osmotic stress, and that this intergenerational adaptation is regulated by insulin signaling to oocytes3. Here, we used proteomics and genetic manipulations to show that insulin signaling to oocytes regulates offspring's ability to adapt to future stress via a mechanism that depends on ETC composition in maternal germ cells/oocytes. Specifically, we found that maternally expressed mutant alleles of nduf-7 (complex I subunit) or isp-1 (complex III subunit) altered offspring's response to osmotic stress at hatching independently of offspring genotype. Furthermore, we found that expressing wild-type isp-1 in maternal germ cells (oocytes) was sufficient to restore offspring's normal response to osmotic stress. Chemical mutagenesis screens revealed that oocyte ETC composition regulates offspring's response to osmotic stress by altering AMP kinase function in offspring which in turn regulates both ATP and glycerol metabolism in offspring in response to continued osmotic stress. To our knowledge, these data are the first to show that changes in oocyte mitochondrial ETC composition can affect an animal phenotype that manifests after embryonic development is complete. The data also suggest that the reason diverse animals exhibit insulin regulated remodeling of oocyte mitochondria might be to tailor offspring metabolism to best match the environment of their mother. Overall design: C. elegans mothers were cultured from the adolescent L4 stage until the first day of adulthood on control NGM culture or on osmotic stress 300mM NaCl culture. The mature oocytes were then dissected and collected in SMART seq buffer.