A novel nematode species from the Siberian permafrost shares adaptive mechanisms for cryptobiotic survival with C. elegans dauer larva.

Some organisms in nature have developed the ability to enter a state of suspended metabolism called cryptobiosis when environmental conditions are unfavorable. This state-transition requires execution of a combination of genetic and biochemical pathways that enable the organism to survive for prolonged periods. Recently, nematode individuals have been reanimated from Siberian permafrost after remaining in cryptobiosis. Preliminary analysis indicates that these nematodes belong to the genera Panagrolaimus and Plectus. Here, we present precise radiocarbon dating indicating that the Panagrolaimus individuals have remained in cryptobiosis since the late Pleistocene (~46,000 years). Phylogenetic inference based on our genome assembly and a detailed morphological analysis demonstrate that they belong to an undescribed species, which we named Panagrolaimus kolymaensis. Comparative genome analysis revealed that the molecular toolkit for cryptobiosis in P. kolymaensis and in C. elegans is partly orthologous. We show that biochemical mechanisms employed by these two species to survive desiccation and freezing under laboratory conditions are similar. Our experimental evidence also reveals that C. elegans dauer larvae can remain viable for longer periods in suspended animation than previously reported. Altogether, our findings demonstrate that nematodes evolved mechanisms potentially allowing them to suspend life over geological time scales.

Quantitative imaging of Caenorhabditis elegans dauer larvae during cryptobiotic transition.

Upon starvation or overcrowding, the nematode Caenorhabditis elegans enters diapause by forming a dauer larva, which can then further survive harsh desiccation in an anhydrobiotic state. We have previously identified the genetic and biochemical pathways essential for survival-but without detailed knowledge of their material properties, the mechanistic understanding of this intriguing phenomenon remains incomplete. Here we employed optical diffraction tomography (ODT) to quantitatively assess the internal mass density distribution of living larvae in the reproductive and diapause stages. ODT revealed that the properties of the dauer larvae undergo a dramatic transition upon harsh desiccation. Moreover, mutants that are sensitive to desiccation displayed structural abnormalities in the anhydrobiotic stage that could not be observed by conventional microscopy. Our advance opens a door to quantitatively assessing the transitions in material properties and structure necessary to fully understand an organism on the verge of life and death.

Exogenous ethanol induces a metabolic switch that prolongs the survival of Caenorhabditis elegans dauer larva and enhances its resistance to desiccation.

The dauer larva of Caenorhabditis elegans, destined to survive long periods of food scarcity and harsh environment, does not feed and has a very limited exchange of matter with the exterior. It was assumed that the survival time is determined by internal energy stores. Here, we show that ethanol can provide a potentially unlimited energy source for dauers by inducing a controlled metabolic shift that allows it to be metabolized into carbohydrates, amino acids, and lipids. Dauer larvae provided with ethanol survive much longer and have greater desiccation tolerance. On the cellular level, ethanol prevents the deterioration of mitochondria caused by energy depletion. By modeling the metabolism of dauers of wild-type and mutant strains with and without ethanol, we suggest that the mitochondrial health and survival of an organism provided with an unlimited source of carbon depends on the balance between energy production and toxic product(s) of lipid metabolism.

C. elegans possess a general program to enter cryptobiosis that allows dauer larvae to survive different kinds of abiotic stress.

All organisms encounter abiotic stress but only certain organisms are able to cope with extreme conditions and enter into cryptobiosis (hidden life). Previously, we have shown that C. elegans dauer larvae can survive severe desiccation (anhydrobiosis), a specific form of cryptobiosis. Entry into anhydrobiosis is preceded by activation of a set of biochemical pathways by exposure to mild desiccation. This process called preconditioning induces elevation of trehalose, intrinsically disordered proteins, polyamines and some other pathways that allow the preservation of cellular functionality in the absence of water. Here, we demonstrate that another stress factor, high osmolarity, activates similar biochemical pathways. The larvae that acquired resistance to high osmotic pressure can also withstand desiccation. In addition, high osmolarity significantly increases the biosynthesis of glycerol making larva tolerant to freezing. Thus, to survive abiotic stress, C. elegans activates a combination of genetic and biochemical pathways that serve as a general survival program.

The glyoxylate shunt is essential for desiccation tolerance in C. elegans and budding yeast.

Many organisms, including species from all kingdoms of life, can survive desiccation by entering a state with no detectable metabolism. To survive, C. elegans dauer larvae and stationary phase S. cerevisiae require elevated amounts of the disaccharide trehalose. We found that dauer larvae and stationary phase yeast switched into a gluconeogenic mode in which metabolism was reoriented toward production of sugars from non-carbohydrate sources. This mode depended on full activity of the glyoxylate shunt (GS), which enables synthesis of trehalose from acetate. The GS was especially critical during preparation of worms for harsh desiccation (preconditioning) and during the entry of yeast into stationary phase. Loss of the GS dramatically decreased desiccation tolerance in both organisms. Our results reveal a novel physiological role for the GS and elucidate a conserved metabolic rewiring that confers desiccation tolerance on organisms as diverse as worm and yeast.

Effect of endogenous Hsp104 chaperone in yeast models of sporadic and familial Parkinson's disease.

Molecular chaperones constitute a major component of the cellular stress response machinery in neurodegenerative diseases, many of which are characterized by the misfolding and aggregation of endogenous cellular proteins into generic amyloid macrostructures. Heterologous expression of the yeast protein remodelling factor Hsp104 has been proposed as a possible therapeutic approach in such disease conditions. Hsp104 is unique in its ability to act as a protein 'disaggregase' by removing smaller units from amyloid fibrils and has no homologue in metazoa. The effect of Hsp104 is strongly modulated by its expression level. We show that at endogenous levels, the presence of Hsp104 has a deleterious effect on protein aggregation in two different strains of yeast. Overexpression of wild-type and mutant human α-synuclein in a well-validated yeast model of Parkinson's disease and in an isogenic Hsp104-deleted strain resulted in lower oxidative stress and reduced damage to cellular proteins in the latter case. This translated to lower cytotoxicity and increased cell viability. Endocytotic defect caused due to aggregation of α-syuclein was also rescued in cells lacking Hsp104. Our results show that the effect of overexpression of a chaperone on protein misfolding/aggregation cannot be predicted from its function in the host expression platform.