Natural variations of cold tolerance and temperature acclimation in Caenorhabditis elegans

The intron binding protein EMB-4 is an opposite regulator of cold and high temperature tolerance in Caenorhabditis elegans

Adaptation and tolerance to changes in heat and cold temperature are essential for survival and proliferation in plants and animals. However, there is no clear information regarding the common molecules between animals and plants. In this study, we found that heat, and cold tolerance of the nematode Caenorhabditis elegans is oppositely regulated by the RNA-binding protein EMB-4, whose plant homolog contains polymorphism causing heat tolerance diversity. Caenorhabditis elegans alters its cold and heat tolerance depending on the previous cultivation temperature, wherein EMB-4 respectively acts as a positive and negative controller of heat and cold tolerance by altering gene expression. Among the genes whose expression is regulated by EMB-4, a phospholipid scramblase, and an acid sphingomyelinase, which are involved in membrane lipid metabolism, were found to play essential roles in the negative regulation of heat tolerance.

G protein-coupled receptor-based thermosensation determines temperature acclimatization of Caenorhabditis elegans

Animals must sense and acclimatize to environmental temperatures for survival, yet their thermosensing mechanisms other than transient receptor potential (TRP) channels remain poorly understood. We identify a trimeric G protein-coupled receptor (GPCR), SRH-40, which confers thermosensitivity in sensory neurons regulating temperature acclimatization in Caenorhabditis elegans. Systematic knockdown of 1000 GPCRs by RNAi reveals GPCRs involved in temperature acclimatization, among which srh-40 is highly expressed in the ADL sensory neuron, a temperature-responsive chemosensory neuron, where TRP channels act as accessorial thermoreceptors. In vivo Ca2+ imaging demonstrates that an srh-40 mutation reduced the temperature sensitivity of ADL, resulting in supranormal temperature acclimatization. Ectopically expressing SRH-40 in a non-warmth-sensing gustatory neuron confers temperature responses. Moreover, temperature-dependent SRH-40 activation is reconstituted in Drosophila S2R+ cells. Overall, SRH-40 may be involved in thermosensory signaling underlying temperature acclimatization. We propose a dual thermosensing machinery through a GPCR and TRP channels in a single sensory neuron.

Temperature acclimation: Temperature shift induces system conversion to cold tolerance in C. elegans

Acclimation to temperature is one of the survival strategies used by organisms to adapt to changing environmental temperatures. Caenorhabditis elegans' cold tolerance is altered by previous cultivation temperature, and similarly, past low-temperature induces a longer lifespan. Temperature is thought to cause a large shift in homeostasis, lipid metabolism, and reproduction in the organism because it is a direct physiological factor during chemical events. This paper will share and discuss what we know so far about the neural and molecular mechanisms that control cold tolerance and lifespan by altering lipid metabolism and physiological characteristics. We hope that this will contribute to a better understanding of how organisms respond to temperature changes.

Head-tail-head neural wiring underlies gut fat storage in Caenorhabditis elegans temperature acclimation

Animals maintain the ability to survive and reproduce by acclimating to environmental temperatures. We showed here that Caenorhabditis elegans exhibited temperature acclimation plasticity, which was regulated by a head-tail-head neural circuitry coupled with gut fat storage. After experiencing cold, C. elegans individuals memorized the experience and were prepared against subsequent cold stimuli. The cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB) regulated temperature acclimation in the ASJ thermosensory neurons and RMG head interneurons, where it modulated ASJ thermosensitivity in response to past cultivation temperature. The PVQ tail interneurons mediated the communication between ASJ and RMG via glutamatergic signaling. Temperature acclimation occurred via gut fat storage regulation by the triglyceride lipase ATGL-1, which was activated by a neuropeptide, FLP-7, downstream of CREB. Thus, a head-tail-head neural circuit coordinated with gut fat influenced experience-dependent temperature acclimation.

Molecular physiology regulating cold tolerance and acclimation of Caenorhabditis elegans

Many organisms can survive and proliferate in changing environmental temperatures. Here, we introduce a molecular physiological mechanism for cold tolerance and acclimation of the nematode Caenorhabditis elegans on the basis of previous reports and a new result. Three types of thermosensory neurons located in the head, ASJ, ASG, and ADL, regulate cold tolerance and acclimation. In ASJ, components of the light-signaling pathway are involved in thermosensation. In ASG, mechanoreceptor DEG-1 acts as thermoreceptor. In ADL, transient receptor potential channels are thermoreceptors; however, the presence of an additional unidentified thermoreceptor is also speculated. ADL thermoresponsivity is modulated by oxygen sensory signaling from URX oxygen sensory neurons via hub interneurons. ASJ releases insulin and steroid hormones that are received by the intestine, which results in lipid composition changing with cold tolerance. Additionally, the intestinal transcriptional alteration affects sperm functions, which in turn affects the thermosensitivity of ASJ; thus, the neuron-intestine-sperm-neuron tissue circuit is essential for cold tolerance.

Cold Survival and Its Molecular Mechanisms in a Locally Adapted Nematode Population

Since Darwin, evolutionary biologists have sought to understand the drivers and mechanisms of natural trait diversity. The field advances toward this goal with the discovery of phenotypes that vary in the wild, their relationship to ecology, and their underlying genes. Here, we established resistance to extreme low temperature in the free-living nematode Caenorhabditis briggsae as an ecological and evolutionary model system. We found that C. briggsae strains of temperate origin were strikingly more cold-resistant than those isolated from tropical localities. Transcriptional profiling revealed expression patterns unique to the resistant temperate ecotype, including dozens of genes expressed at high levels even after multiple days of cold-induced physiological slowdown. Mutational analysis validated a role in cold resistance for seven such genes. These findings highlight a candidate case of robust, genetically complex adaptation in an emerging model nematode, and shed light on the mechanisms at play.

OSM-9 and OCR-2 TRPV channels are accessorial warm receptors in Caenorhabditis elegans temperature acclimatisation

Caenorhabditis elegans (C. elegans) exhibits cold tolerance and temperature acclimatisation regulated by a small number of head sensory neurons, such as the ADL temperature-sensing neurons that express three transient receptor potential vanilloid (TRPV) channel subunits, OSM-9, OCR-2, and OCR-1. Here, we show that an OSM-9/OCR-2 regulates temperature acclimatisation and acts as an accessorial warmth-sensing receptor in ADL neurons. Caenorhabditis elegans TRPV channel mutants showed abnormal temperature acclimatisation. Ectopic expression of OSM-9 and OCR-2 in non-warming-responsive gustatory neurons in C. elegans and Xenopus oocytes revealed that OSM-9 and OCR-2 cooperatively responded to warming; however, neither TRPV subunit alone was responsive to warming. A warming-induced OSM-9/OCR-2-mediated current was detectable in Xenopus oocytes, yet ADL in osm-9 ocr-2 double mutant responds to warming; therefore, an OSM-9/OCR-2 TRPV channel and as yet unidentified temperature receptor might coordinate transmission of temperature signalling in ADL temperature-sensing neurons. This study demonstrates direct sensation of warming by TRPV channels in C. elegans.

Deep learning-enabled analysis reveals distinct neuronal phenotypes induced by aging and cold-shock

BACKGROUND

Access to quantitative information is crucial to obtain a deeper understanding of biological systems. In addition to being low-throughput, traditional image-based analysis is mostly limited to error-prone qualitative or semi-quantitative assessment of phenotypes, particularly for complex subcellular morphologies. The PVD neuron in Caenorhabditis elegans, which is responsible for harsh touch and thermosensation, undergoes structural degeneration as nematodes age characterized by the appearance of dendritic protrusions. Analysis of these neurodegenerative patterns is labor-intensive and limited to qualitative assessment.

RESULTS

In this work, we apply deep learning to perform quantitative image-based analysis of complex neurodegeneration patterns exhibited by the PVD neuron in C. elegans. We apply a convolutional neural network algorithm (Mask R-CNN) to identify neurodegenerative subcellular protrusions that appear after cold-shock or as a result of aging. A multiparametric phenotypic profile captures the unique morphological changes induced by each perturbation. We identify that acute cold-shock-induced neurodegeneration is reversible and depends on rearing temperature and, importantly, that aging and cold-shock induce distinct neuronal beading patterns.

CONCLUSION

The results of this work indicate that implementing deep learning for challenging image segmentation of PVD neurodegeneration enables quantitatively tracking subtle morphological changes in an unbiased manner. This analysis revealed that distinct patterns of morphological alteration are induced by aging and cold-shock, suggesting different mechanisms at play. This approach can be used to identify the molecular components involved in orchestrating neurodegeneration and to characterize the effect of other stressors on PVD degeneration.

Transcriptomic profiling revealed key signaling pathways for cold tolerance and acclimation of two carp species

Background

Closely related species of the carp family (Cyprinidae) have evolved distinctive abilities to survive under cold stress, but molecular mechanisms underlying the generation of cold resistance remain largely unknown. In this study, we compared transcriptomic profiles of two carp species to identify key factors and pathways for cold tolerance and acclimation.

Results

Larvae of Songpu mirror carp and Barbless carp that were pretreated at 18 °C for 24 h significantly improved their survival rates under lethal cold temperature at 8 °C or 10 °C, indicating that two carp species possess the ability of cold acclimation. However, Songpu mirror carp exhibited stronger abilities of cold tolerance and acclimation than Barbless carp. Transcriptomic profiles of Songpu mirror carp and Barbless carp larvae at 28 °C and 18 °C were compared during cold acclimation through RNA-seq. Differentially expressed genes that are closely associated with the differences in cold acclimation between two carp species were identified through bioinformatics and Venn’s diagram analysis. GO enrichment analysis of these genes indicated that cellular component assembly involved in morphogenesis, secondary alcohol metabolism and drug transport were the most up-regulated biological processes during cold acclimation of Songpu mirror carp. Conversely, positive regulation of macroautophagy, intracellular protein transport, and organonitrogen compound catabolism were the most down-regulated biological processes during cold acclimation of Barbless carp. KEGG enrichment analysis revealed that factors in the FoxO-related signaling pathways are mainly responsible for the development of differences in cold tolerance and acclimation between two carp species since altering the phosphorylation of key proteins in the FoxO-related signaling pathways with inhibitors or an activator significantly decreased the cold tolerance and acclimation of Songpu mirror carp. These data provided key clues for dissection of molecular mechanisms underlying the development of cold tolerance and acclimation in carps.

Conclusions

These findings indicate that larvae of two carp species possess different abilities of cold tolerance and can build cold acclimation under mild low temperature. Multiple biological processes and FoxO-related signaling pathways are closely associated with the development of differences in cold tolerance and acclimation between two carp species.

The mechanoreceptor DEG-1 regulates cold tolerance in Caenorhabditis elegans

Caenorhabditis elegans mechanoreceptors located in ASG sensory neurons have been found to sense ambient temperature, which is a key trait for animal survival. Here, we show that experimental loss of xanthine dehydrogenase (XDH-1) function in AIN and AVJ interneurons results in reduced cold tolerance and atypical neuronal response to changes in temperature. These interneurons connect with upstream neurons such as the mechanoreceptor-expressing ASG. Ca²⁺ imaging revealed that ASG neurons respond to warm temperature via the mechanoreceptor DEG-1, a degenerin/epithelial Na⁺ channel (DEG/ENaC), which in turn affects downstream AIN and AVJ circuits. Ectopic expression of DEG-1 in the ASE gustatory neuron results in the acquisition of warm sensitivity, while electrophysiological analysis revealed that DEG-1 and human MDEG1 were involved in warm sensation. Taken together, these results suggest that cold tolerance is regulated by mechanoreceptor-mediated circuit calculation.

Wood ash decreases cadmium toxicity to the soil nematode Caenorhabditis elegans

Wood ash is a beneficial fertilizer and liming agent in nutrient depleted soils, but it also contains considerable amounts of cadmium (Cd), which can be toxic to organisms in the environment. Therefore, risk assessments regarding utilization of wood ash is required. Here, we studied how wood ash (applied in doses equivalent to 0, 3 and 6 t ha^-1) and Cd (applied in doses of 0, 10, 150, 300, 600, 1200 and 2000 mg kg^-1) affected growth of the soil nematode Caenorhabditis elegans. The treatments were combined in a full factorial design. Wood ash alone greatly stimulated both soil respiration and growth of C. elegans, whereas Cd alone had a toxic effect. However, unrealistically high Cd levels were needed to severely affect growth of C. elegans and soil respiration, especially soil respiration was very resilient to Cd amendment. Ash addition decreased Cd toxicity to C. elegans, with an EC₅₀ value of 390 mg Cd kg^-1 in the 3 t ash ha^-1 treatment, and an increase of EC₅₀ to 1894 mg Cd kg^-1 in the 6 t ash ha^-1 treatment. This is probably because ash increases the Cd sorption capacity of the soil, and thereby decreases the bio-availability of Cd. The results suggest that there is no acute toxic effect of Cd to nematodes associated with wood ash recycling; in fact, our results suggest that ash actually decrease Cd toxicity.

Cold acclimation via the KQT-2 potassium channel is modulated by oxygen in Caenorhabditis elegans

Adaptive responses to external temperatures are essential for survival in changing environments. We show here that environmental oxygen concentration affects cold acclimation in Caenorhabditis elegans and that this response is regulated by a KCNQ-type potassium channel, KQT-2. Depending on culture conditions, kqt-2 mutants showed supranormal cold acclimation, caused by abnormal thermosensation in ADL chemosensory neurons. ADL neurons are responsive to temperature via transient receptor potential channels-OSM-9, OCR-2, and OCR-1-with OCR-1 negatively regulating ADL function. Similarly, KQT-2 and KQT-3 regulate ADL activity, with KQT-2 positively regulating ADL function. Abnormal cold acclimation and acute temperature responses of ADL neurons in kqt-2 mutants were suppressed by an oxygen-receptor mutation in URX coelomic sensory neurons, which are electrically connected to ADL via RMG interneurons. Likewise, low oxygen suppressed supranormal kqt-2 cold acclimation. These data thus demonstrate a simple neuronal circuit integrating two different sensory modalities, temperature and oxygen, that determines cold acclimation.

Endoribonuclease ENDU-2 regulates multiple traits including cold tolerance via cell autonomous and nonautonomous controls in Caenorhabditis elegans

Environmental temperature acclimation is essential to animal survival, yet thermoregulation mechanisms remain poorly understood. We demonstrate cold tolerance in Caenorhabditis elegans as regulated by paired ADL chemosensory neurons via Ca²⁺-dependent endoribonuclease (EndoU) ENDU-2. Loss of ENDU-2 function results in life span, brood size, and synaptic remodeling abnormalities in addition to enhanced cold tolerance. Enzymatic ENDU-2 defects localized in the ADL and certain muscle cells led to increased cold tolerance in endu-2 mutants. Ca²⁺ imaging revealed ADL neurons were responsive to temperature stimuli through transient receptor potential (TRP) channels, concluding that ADL function requires ENDU-2 action in both cell-autonomous and cell-nonautonomous mechanisms. ENDU-2 is involved in caspase expression, which is central to cold tolerance and synaptic remodeling in dorsal nerve cord. We therefore conclude that ENDU-2 regulates cell type-dependent, cell-autonomous, and cell-nonautonomous cold tolerance.

Diverse Regulation of Temperature Sensation by Trimeric G-Protein Signaling in Caenorhabditis elegans

Temperature sensation by the nervous system is essential for life and proliferation of animals. The molecular-physiological mechanisms underlying temperature signaling have not been fully elucidated. We show here that diverse regulatory machinery underlies temperature sensation through trimeric G-protein signaling in the nematode Caenorhabditis elegans. Molecular-genetic studies demonstrated that cold tolerance is regulated by additive functions of three Gα proteins in a temperature-sensing neuron, ASJ, which is also known to be a light-sensing neuron. Optical recording of calcium concentration in ASJ upon temperature-changes demonstrated that three Gα proteins act in different aspects of temperature signaling. Calcium concentration changes in ASJ upon temperature change were unexpectedly decreased in a mutant defective in phosphodiesterase, which is well known as a negative regulator of calcium increase. Together, these data demonstrate commonalities and differences in the molecular components concerned with light and temperature signaling in a single sensory neuron.