Tardigrade small heat shock proteins can limit desiccation-induced protein aggregation

Small heat shock proteins (sHSPs) are chaperones with well-characterized roles in heat stress, but potential roles for sHSPs in desiccation tolerance have not been as thoroughly explored. We identified nine sHSPs from the tardigrade Hypsibius exemplaris, each containing a conserved alpha-crystallin domain flanked by disordered regions. Many of these sHSPs are highly expressed. Multiple tardigrade and human sHSPs could improve desiccation tolerance of E. coli, suggesting that the capacity to contribute to desicco-protection is a conserved property of some sHSPs. Purification and subsequent analysis of two tardigrade sHSPs, HSP21 and HSP24.6, revealed that these proteins can oligomerize in vitro. These proteins limited heat-induced aggregation of the model enzyme citrate synthase. Heterologous expression of HSP24.6 improved bacterial heat shock survival, and the protein significantly reduced heat-induced aggregation of soluble bacterial protein. Thus, HSP24.6 likely chaperones against protein aggregation to promote heat tolerance. Furthermore, HSP21 and HSP24.6 limited desiccation-induced aggregation and loss of function of citrate synthase. This suggests a mechanism by which tardigrade sHSPs promote desiccation tolerance, by limiting desiccation-induced protein aggregation, thereby maintaining proteostasis and supporting survival. These results suggest that sHSPs provide a mechanism of general stress resistance that can also be deployed to support survival during anhydrobiosis.Small heat shock proteins from the tardigrade Hypsibius exemplaris are shown to provide a mechanism of stress resistance that can support not just heat tolerance but desiccation tolerance as well

Stress biology:Complexity and multifariousness in health and disease

Preserving and regulating cellular homeostasis in the light of changing environmental conditions or developmental processes is of pivotal importance for single cellular and multicellular organisms alike. To counteract an imbalance in cellular homeostasis transcriptional programs evolved, called the heat shock response, unfolded protein response, and integrated stress response, that act cell-autonomously in most cells but in multicellular organisms are subjected to cell-nonautonomous regulation. These transcriptional programs downregulate the expression of most genes but increase the expression of heat shock genes, including genes encoding molecular chaperones and proteases, proteins involved in the repair of stress-induced damage to macromolecules and cellular structures. Sixty-one years after the discovery of the heat shock response by Ferruccio Ritossa, many aspects of stress biology are still enigmatic. Recent progress in the understanding of stress responses and molecular chaperones was reported at the 12th International Symposium on Heat Shock Proteins in Biology, Medicine and the Environment in the Old Town Alexandria, VA, USA from 28th to 31st of October 2023.</p

Correction: Maternal Diet and Insulin-Like Signaling Control Intergenerational Plasticity of Progeny Size and Starvation Resistance.

[This corrects the article DOI: 10.1371/journal.pgen.1006396.]

Mechanisms of Desiccation Tolerance: Themes and Variations in Brine Shrimp, Roundworms, and Tardigrades

Water is critical for the survival of most cells and organisms. Remarkably, a small number of multicellular animals are able to survive nearly complete drying. The phenomenon of anhydrobiosis, or life without water, has been of interest to researchers for over 300 years. In this review we discuss advances in our understanding of protectants and mechanisms of desiccation tolerance that have emerged from research in three anhydrobiotic invertebrates: brine shrimp (Artemia), roundworms (nematodes), and tardigrades (water bears). Discovery of molecular protectants that allow each of these three animals to survive drying diversifies our understanding of desiccation tolerance, and convergent themes suggest mechanisms that may offer a general model for engineering desiccation tolerance in other contexts

Maternal Diet and Insulin-Like Signaling Control Intergenerational Plasticity of Progeny Size and Starvation Resistance

<div><p>Maternal effects of environmental conditions produce intergenerational phenotypic plasticity. Adaptive value of these effects depends on appropriate anticipation of environmental conditions in the next generation, and mismatch between conditions may contribute to disease. However, regulation of intergenerational plasticity is poorly understood. Dietary restriction (DR) delays aging but maternal effects have not been investigated. We demonstrate maternal effects of DR in the roundworm <i>C</i>. <i>elegans</i>. Worms cultured in DR produce fewer but larger progeny. Nutrient availability is assessed in late larvae and young adults, rather than affecting a set point in young larvae, and maternal age independently affects progeny size. Reduced signaling through the insulin-like receptor <i>daf-2</i>/InsR in the maternal soma causes constitutively large progeny, and its effector <i>daf-16/</i>FoxO is required for this effect. <i>nhr-49/</i>Hnf4, <i>pha-4/</i>FoxA, and <i>skn-1/</i>Nrf also regulate progeny-size plasticity. Genetic analysis suggests that insulin-like signaling controls progeny size in part through regulation of <i>nhr-49</i>/Hnf4, and that <i>pha-4</i>/FoxA and <i>skn-1</i>/Nrf function in parallel to insulin-like signaling and <i>nhr-49</i>/Hnf4. Furthermore, progeny of DR worms are buffered from adverse consequences of early-larval starvation, growing faster and producing more offspring than progeny of worms fed <i>ad libitum</i>. These results suggest a fitness advantage when mothers and their progeny experience nutrient stress, compared to an environmental mismatch where only progeny are stressed. This work reveals maternal provisioning as an organismal response to DR, demonstrates potentially adaptive intergenerational phenotypic plasticity, and identifies conserved pathways mediating these effects.</p></div

Model for the impact of maternal diet on progeny size and starvation resistance.

<p>A) Mothers that experience conditions of dietary restriction are smaller and produce fewer but larger embryos and L1 progeny. Progeny of DR mothers are resistant to developmental delay and reduced brood size after recovery from extended L1 starvation. B) <i>daf-2</i>/InsR acts through <i>daf-16</i>/FoxO in the soma to regulate embryo size. <i>nhr-49</i> is repressed by <i>daf-16</i> in DR, and <i>nhr-49</i> functions in AL to reduce progeny size. <i>skn-1</i> and <i>pha-4</i> are active in DR and function in parallel to insulin-like signaling and <i>nhr-49</i> to increase progeny size. Insulin-like signaling is required to increase progeny size in food dilution DR but not the <i>eat-2</i> genetic model (dashed line).</p

DR reduces adult size and early fecundity.

<p>A,B) Representative adult worms after 96 hr in culture for WT and <i>eat-2(ad465)</i> are shown. C,D) Representative adult worms cultured in AL or DR for 96 hr (starting from L1 arrest) are shown. Scale bars in A-D are 200 μm. E) Adult length (96 hr after L1 arrest) is plotted for WT and <i>eat-2(ad465)</i>. F) Adult length (96 hr after L1 arrest) is plotted for AL and DR. Mean and SEM are plotted in E and F (*p<0.05, paired t-test, n = 3 and 4, respectively). G,H) Representative DAPI-stained worms cultured in AL or DR conditions for 96 hr are shown. Scale bars are 20 μm. I) The average proportion of worms with at least one embryo <i>in utero</i> is plotted against time in culture (starting from L1 arrest). Data are from sampling 5 independent biological replicates. J) The number of offspring laid after 96 hr in AL or DR culture is plotted (*p = 0.02, paired t-test, n = 3). Data are pooled and presented as a boxplot reflecting the quartiles. Whiskers extend to the lowest and highest data points within 1.5x the interquartile range. Outliers appear as dots, and diamonds depict the mean value of the pooled data.</p

Maternal insulin-like signaling mediates the effect of diet in liquid culture on progeny size.

<p>A-B) Progeny embryo length for a variety of genotypes and RNAi treatments is plotted. C) Progeny embryo length for self and cross progeny resulting from crossing WT GFP+ males with WT and <i>daf-2</i> hermaphrodites is plotted. A-C) **p<0.01, ****p<0.0001, paired t-test, n = 3. D-F) Progeny embryo length is plotted for <i>daf-2</i> RNAi in <i>ppw-1</i> and <i>rrf-1</i> backgrounds (D), <i>daf-2</i> and <i>daf-16</i> RNAi in the <i>eat-2</i> DR system (E) and <i>daf-2</i>, <i>daf-16</i>, and double mutants in the liquid culture DR system (F). p_int indicates the p-value for the interaction term from a 2-way ANOVA for the two strains plotted. Mean and SEM are plotted for A-F. Note the expanded scale of the y-axis in E.</p

<i>pha-4</i>/FoxA, <i>skn-1</i>/Nrf, and <i>nhr-49</i>/Hnf4 are required for progeny-size plasticity.

<p>A-D) Progeny embryo length is plotted for RNAi of <i>pha-4</i>, <i>skn-1</i>, and <i>nhr-49</i> in the <i>eat-2</i> system (A), <i>nhr-49(nr2041)</i> in the food dilution system (B), RNAi of <i>daf-16</i>, <i>pha-4</i>, <i>skn-1</i>, and <i>nhr-49</i> in <i>daf-2(e1370)</i> (C), and RNAi of <i>daf-16</i>, <i>skn-1</i>, and <i>pha-4</i> in <i>nhr-49(nr2041)</i> (D). Mean and SEM are plotted. p_int indicates the p-value for the interaction term from a 2-way ANOVA for the two strains plotted.</p