Environmental stress during early development in animals can have profound effects on adult phenotypes via programmed changes in gene expression. Using the nematode C. elegans, we demonstrated previously that adults retain a cellular memory of their developmental experience that is manifested by differences in gene expression and life history traits; however, the sophistication of this system in response to different environmental stresses, and how it dictates phenotypic plasticity in adults that contribute to increased fitness in response to distinct environmental challenges, was unknown. Using transcriptional profiling, we show here that C. elegans adults indeed retain distinct cellular memories of different environmental conditions. We identified approximately 500 genes in adults that entered dauer due to starvation that exhibit significant opposite (“seesaw”) transcriptional phenotypes compared to adults that entered dauer due to crowding, and are distinct from animals that bypassed dauer. Moreover, we show that two-thirds of the genes in the genome experience a 2-fold or greater seesaw trend in gene expression, and based upon the direction of change, are enriched in large, tightly linked regions on different chromosomes. Importantly, these transcriptional programs correspond to significant changes in brood size depending on the experienced stress. In addition, we demonstrate that while the observed seesaw gene expression changes occur in both somatic and germline tissue, only starvation-induced changes require a functional GLP-4 protein necessary for germline development, and both programs require the Argonaute CSR-1. Thus, our results suggest that signaling between the soma and the germ line can generate phenotypic plasticity as a result of early environmental experience, and likely contribute to increased fitness in adverse conditions and the evolution of the C. elegans genome.
In animals, early-life stress can result in programmed changes in gene expression that can affect their adult phenotype. In C. elegans nematodes, starvation during the first larval stage promotes entry into a stress-resistant dauer stage until environmental conditions improve. Adults that have experienced dauer (postdauers) retain a memory of early-life starvation that results in gene expression changes and reduced fecundity. Here we show that the endocrine pathways attributed to the regulation of somatic aging in C. elegans adults lacking a functional germline also regulate the reproductive phenotypes of postdauer adults that experienced early-life starvation. We demonstrate that postdauer adults reallocate fat to benefit progeny at the expense of the parental somatic fat reservoir and exhibit increased longevity compared to controls. Our results also show that the modification of somatic fat stores due to parental starvation memory is inherited in the F1 generation and may be the result of crosstalk between somatic and reproductive tissues mediated by the germline nuclear RNAi pathway.
SummaryEarly life stress of an animal often results in changes in gene expression that correspond with changes in their adult phenotype. In the nematode C. elegans, starvation during early larval stages promotes entry into a non-feeding, stress-resistant stage named dauer until environmental conditions improve. Here we show that the endocrine signaling attributed to the somatic aging pathways in C. elegans adults lacking a functional germline also regulate the reproductive phenotypes of adults that have experienced dauer as a result of early life starvation. Postdauer adults modulate their fatty acid metabolism in order to re-allocate fat reserves in a manner benefitting their progeny at the expense of the parental somatic fat reservoir. Our results also show that the metabolic plasticity in postdauer animals and the inheritance of ancestral starvation memory in the progeny are a result of crosstalk between somatic and reproductive tissues mediated by the HRDE-1 nuclear RNAi Argonaute.
In animals, early-life starvation can program gene expression changes that result in profound effects on adult phenotypes. For C. elegans nematodes, passage through the stress-resistant dauer diapause stage due to early-life starvation establishes a cellular memory that manifests as increased metabolism and decreased fecundity compared to continuously developed adults. To further investigate the connection between metabolism and reproduction, we supplemented the diet of postdauer adults with different fatty acids and examined their life history traits. Here, we show that dietary oleic acid (OA) supplementation uniquely increases the fecundity of both postdauer and continuously developed adults in a DAF-12 steroid signaling dependent manner, potentially through the increased expression of fat-7 Δ9-desaturase and vit-2 vitellogen genes. In addition, OA may rescue increased ferroptosis in postdauer germ lines and has complex effects on adult lifespan depending on life history. Together, our results suggest a model where OA modifies DAF-12 activity to positively regulate fecundity, metabolism, and lifespan in adults.
Mating strategies, whether sexual or asexual, confer unique costs and benefits to populations and species that facilitate evolutionary processes. In wild isolates of Caenorhabditis elegans, mating strategies are dependent on developmental history. Outcrossing levels significantly increase when one or both parents have transiently passed through the stress-resistant dauer diapause stage. However, the molecular mechanisms of how life history alters mating strategies have not been systematically explored. Sex-specific responses to pheromones are a major driver of mating behaviors in C. elegans. We demonstrated previously that postdauer hermaphrodites exhibit a decreased avoidance of the pheromone ascr#3 due to the downregulation of the osm-9 TRPV channel gene in postdauer ADL neurons. Thus, we hypothesized that altered responses to pheromones in postdauer animals could contribute to increased outcrossing. We conducted mating assays using wild type N2 Bristol, as well as daf-3/co-SMAD and mut-16/Mutator strains that fail to downregulate osm-9 in postdauer hermaphrodite ADL neurons. First, we show that the outcrossing level of N2 Bristol correlated with the developmental history of males, and that postdauer males exhibited an increased ability to detect mates via pheromones compared to continuously developed males. In addition, DAF-3 plays a critical role in postdauer males to regulate mating, while playing a more minor role in hermaphrodites. Furthermore, the mut-16 strain exhibited negligible outcrossing, and attempts to rescue the outcrossing phenotype resulted in transgenerational sterility due to germline defects. Together, our results suggest a model whereby mating strategy is driven by developmental history under combinatorial control of TGF-β and RNAi pathways.
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