The C. elegans Hypertonic Stress Response: Big Insights from Shrinking Worms

The Caenorhabditis elegans cuticle and precuticle: a model for studying dynamic apical extracellular matrices in vivo

Apical extracellular matrices (aECMs) coat the exposed surfaces of animal bodies to shape tissues, influence social interactions, and protect against pathogens and other environmental challenges. In the nematode Caenorhabditis elegans, collagenous cuticle and zona pellucida protein-rich precuticle aECMs alternately coat external epithelia across the molt cycle and play many important roles in the worm's development, behavior, and physiology. Both these types of aECMs contain many matrix proteins related to those in vertebrates, as well as some that are nematode-specific. Extensive differences observed among tissues and life stages demonstrate that aECMs are a major feature of epithelial cell identity. In addition to forming discrete layers, some cuticle components assemble into complex substructures such as ridges, furrows, and nanoscale pillars. The epidermis and cuticle are mechanically linked, allowing the epidermis to sense cuticle damage and induce protective innate immune and stress responses. The C. elegans model, with its optical transparency, facilitates the study of aECM cell biology and structure/function relationships and all the myriad ways by which aECM can influence an organism.

A DNA nanodevice for mapping sodium at single-organelle resolution

Cellular sodium ion (Na+) homeostasis is integral to organism physiology. Our current understanding of Na+ homeostasis is largely limited to Na+ transport at the plasma membrane. Organelles may also contribute to Na+ homeostasis; however, the direction of Na+ flow across organelle membranes is unknown because organellar Na+ cannot be imaged. Here we report a pH-independent, organelle-targetable, ratiometric probe that reports lumenal Na+. It is a DNA nanodevice containing a Na+-sensitive fluorophore, a reference dye and an organelle-targeting domain. By measuring Na+ at single endosome resolution in mammalian cells and Caenorhabditis elegans, we discovered that lumenal Na+ levels in each stage of the endolysosomal pathway exceed cytosolic levels and decrease as endosomes mature. Further, we find that lysosomal Na+ levels in nematodes are modulated by the Na+/H+ exchanger NHX-5 in response to salt stress. The ability to image subcellular Na+ will unveil mechanisms of Na+ homeostasis at an increased level of cellular detail.

Improved resilience and proteostasis mediate longevity upon DAF-2 degradation in old age

Little is known about the possibility of reversing age-related biological changes when they have already occurred. To explore this, we have characterized the effects of reducing insulin/IGF-1 signaling (IIS) during old age. Reduction of IIS throughout life slows age-related decline in diverse species, most strikingly in the nematode Caenorhabditis elegans. Here we show that even at advanced ages, auxin-induced degradation of DAF-2 in single tissues, including neurons and the intestine, is still able to markedly increase C. elegans lifespan. We describe how reversibility varies among senescent changes. While senescent pathologies that develop in mid-life were not reversed, there was a rejuvenation of the proteostasis network, manifesting as a restoration of the capacity to eliminate otherwise intractable protein aggregates that accumulate with age. Moreover, resistance to several stressors was restored. These results support several new conclusions. (1) Loss of resilience is not solely a consequence of pathologies that develop in earlier life. (2) Restoration of proteostasis and resilience by inhibiting IIS is a plausible cause of the increase in lifespan. And (3), most interestingly, some aspects of the age-related transition from resilience to frailty can be reversed to a certain extent. This raises the possibility that the effect of IIS and related pathways on resilience and frailty during aging in higher animals might possess some degree of reversibility.

Selection and the direction of phenotypic evolution

Predicting adaptive phenotypic evolution depends on invariable selection gradients and on the stability of the genetic covariances between the component traits of the multivariate phenotype. We describe the evolution of six traits of locomotion behavior and body size in the nematode Caenorhabditis elegans for 50 generations of adaptation to a novel environment. We show that the direction of adaptive multivariate phenotypic evolution can be predicted from the ancestral selection differentials, particularly when the traits were measured in the new environment. Interestingly, the evolution of individual traits does not always occur in the direction of selection, nor are trait responses to selection always homogeneous among replicate populations. These observations are explained because the phenotypic dimension with most of the ancestral standing genetic variation only partially aligns with the phenotypic dimension under directional selection. These findings validate selection theory and suggest that the direction of multivariate adaptive phenotypic evolution is predictable for tens of generations.

Extracellular proteins OSM-7 and OSM-8 are required for stress response gene regulation at all post-embryonic stages

Nematode cuticles are extracellular matrices (ECMs) that function as structural support and permeability barriers. Genetic disruption of specific cuticle collagen structures or secreted epidermal proteins in C. elegans activates stress response genes in epithelial cells suggesting the presence of an extracellular damage signaling mechanism. Cuticles are replaced during development via molting but investigations of extracellular signaling to stress responses have focused on adults. In our current study, we measured cuticle phenotypes and stress response gene expression in all post-embryonic stages of mutant strains for a collagen and two secreted epidermal proteins to gain insights into developmental patterns.

Transcriptomic and Proteomic Analysis of Marine Nematode Litoditis marina Acclimated to Different Salinities

Salinity is a critical abiotic factor for all living organisms. The ability to adapt to different salinity environments determines an organism’s survival and ecological niches. Litoditis marina is a euryhaline marine nematode widely distributed in coastal ecosystems all over the world, although numerous genes involved in its salinity response have been reported, the adaptive mechanisms underlying its euryhalinity remain unexplored. Here, we utilized worms which have been acclimated to either low-salinity or high-salinity conditions and evaluated their basal gene expression at both transcriptomic and proteomic levels. We found that several conserved regulators, including osmolytes biosynthesis genes, transthyretin-like family genes, V-type H⁺-transporting ATPase and potassium channel genes, were involved in both short-term salinity stress response and long-term acclimation processes. In addition, we identified genes related to cell volume regulation, such as actin regulatory genes, Rho family small GTPases and diverse ion transporters, which might contribute to hyposaline acclimation, while the glycerol biosynthesis genes gpdh-1 and gpdh-2 accompanied hypersaline acclimation in L. marina. This study paves the way for further in-depth exploration of the adaptive mechanisms underlying euryhalinity and may also contribute to the study of healthy ecosystems in the context of global climate change.