C. elegans have several strategies for surviving starvation conditions. If starved during the last stage of larval development, C. elegans can enter adult reproductive diapause (ARD), resulting in shrinkage of the germline cells, morphological changes to the gonad arms, and reversible sterility. Separate investigations of the ARD phenotype have resulted in different conclusions about the fate of embryos during ARD. Angelo and Van Gilst characterized adult worms in ARD to have shrunken germlines as well as 1-2 arrested embryos (1). Kimble, whilst getting adult worms to successfully arrest reproduction, did not observe arrested embryos in the ARD animals (2).Our initial focus for investigating ARD was to establish a protocol for reliably inducing worms in to the arrested state. The key aspect of this protocol is the timing at which worms are introduced on to starvation plates. Once the protocol was developed, we obtained evidence that all wild-type adults that enter ARD contain embryos. We demonstrate that these embryos are not dead but are instead in a state of developmental arrest. Whilst testing different genotypes involved in stress response and insulin signaling, we found
daf-16 mutant worms did not show the embryo arrest characteristic of wild-type ARD animals. These findings that reduced insulin signaling promotes arrest of embryos in ARD. We speculate that the discordant results previously reported regarding the presence of embryos in adults that are in starvation-induced ARD (1,2) may be explained by variations in experimental protocol.1) Angelo, G. and M. Van Gilst. 2009. Starvation Protects Germline Stem Cells and Extends Reproductive Longevity in C. elegans. Science 326: 954-958.2) Kimble, J. and H. Seidel. 2011. The Oogenic Germline Starvation Response in C. elegans. PLoS ONE 6(12):
e28074.