Atsushi Kuhara

Reconstruction of Spatial Thermal Gradient Encoded in Thermosensory Neuron AFD in Caenorhabditis elegans.

During navigation, animals process temporal sequences of sensory inputs to evaluate the surrounding environment. Thermotaxis of Caenorhabditis elegans is a favorable sensory behavior to elucidate how navigating animals process sensory signals from the environment. Sensation and storage of temperature information by a bilaterally symmetric pair of thermosensory neurons, AFD, is essential for the animals to migrate toward the memorized temperature on a thermal gradient. However, the encoding mechanisms of the spatial environment with the temporal AFD activity during navigation remain to be elucidated. Here, we show how the AFD neuron encodes sequences of sensory inputs to perceive spatial thermal environment. We used simultaneous calcium imaging and tracking system for a freely moving animal and characterized the response property of AFD to the thermal stimulus during thermotaxis. We show that AFD neurons respond to shallow temperature increases with intermittent calcium pulses and detect temperature differences with a critical time window of 20 s, which is similar to the timescale of behavioral elements of C. elegans, such as turning. Convolution of a thermal stimulus and the identified response property successfully reconstructs AFD activity. Conversely, deconvolution of the identified response kernel and AFD activity reconstructs the shallow thermal gradient with migration trajectory, indicating that AFD activity and the migration trajectory are sufficient as the encoded signals for thermal environment. Our study demonstrates bidirectional transformation between environmental thermal information and encoded neural activity. SIGNIFICANCE STATEMENT Deciphering how information is encoded in the nervous system is an important challenge for understanding the principles of information processing in neural circuits. During navigation behavior, animals transform spatial information to temporal patterns of neural activity. To elucidate how a sensory system achieves this transformation, we focused on a thermosensory neuron in Caenorhabditis elegans called AFD, which plays a major role in a sensory behavior. Using tracking and calcium imaging system for freely moving animals, we identified the response property of the AFD. The identified response property enabled us to reconstruct both neural activity from a temperature stimulus and a spatial thermal environment from neural activity. These results shed light on how a sensory system encodes the environment.

Sperm Affects Head Sensory Neuron in Temperature Tolerance of Caenorhabditis elegans.

Tolerance to environmental temperature change is essential for the survival and proliferation of animals. The process is controlled by various body tissues, but the orchestration of activity within the tissue network has not been elucidated in detail. Here, we show that sperm affects the activity of temperature-sensing neurons (ASJ) that control cold tolerance in Caenorhabditis elegans. Genetic impairment of sperm caused abnormal cold tolerance, which was unexpectedly restored by impairment of temperature signaling in ASJ neurons. Calcium imaging revealed that ASJ neuronal activity in response to temperature was decreased in sperm mutant gsp-4 with impaired protein phosphatase 1 and rescued by expressing gsp-4 in sperm. Genetic analysis revealed a feedback network in which ASJ neuronal activity regulates the intestine through insulin and a steroid hormone, which then affects sperm and, in turn, controls ASJ neuronal activity. Thus, we propose that feedback between sperm and a sensory neuron mediating temperature tolerance.

Caenorhabditis elegans homologue of Prox1/Prospero is expressed in the glia and is required for sensory behavior and cold tolerance

The Caenorhabditis elegans (C. elegans) amphid sensory organ contains only 4 glia‐like cells and 24 sensory neurons, providing a simple model for analyzing glia or neuron‐glia interactions. To better characterize glial development and function, we carried out RNA interference screening for transcription factors that regulate the expression of an amphid sheath glial cell marker and identified pros‐1, which encodes a homeodomain transcription factor homologous to Drosophila prospero/mammalian Prox1, as a positive regulator. The functional PROS‐1::EGFP fusion protein was localized in the nuclei of the glia and the excretory cell but not in the amphid sensory neurons. pros‐1 deletion mutants exhibited larval lethality, and rescue experiments showed that pros‐1 and human Prox1 transgenes were able to rescue the larval lethal phenotype, suggesting that pros‐1 is a functional homologue of mammalian Prox1, at least partially. We further found that the structure and functions of sensory neurons, such as the morphology of sensory endings, sensory behavior and sensory‐mediated cold tolerance, appeared to be affected by the pros‐1 RNAi. Together, our results show that the C. elegans PROS‐1 is a transcriptional regulator in the glia but is involved not only in sensory behavior but also in sensory‐mediated physiological tolerance.

Molecular mechanism for trimetric G protein-coupled thermosensation and synaptic regulation in the temperature response circuit of Caenorhabditis elegans.

How the nervous system controls the sensation and memory of information from the environment is an essential question. The nematode Caenorhabditis elegans is a useful model for elucidating neural information processing that mediates sensation and memory. The entire nervous system of C. elegans consists of only 302 neurons, and their wiring diagram has been revealed by electron microscopy analysis. Here, we review the molecular and physiological mechanisms responsible for the neural circuit-mediated temperature-seeking behavior (thermotaxis) in C. elegans. Recent molecular biology studies and optogenetic analyses, such as the optical manipulation of neural activity, and neural imaging have revealed the novel concept of neural calculation. Most significantly, trimetric G proteincoupled thermosensation, single sensory neuron-based memory, and the orchestrated synaptic transmission system have been elucidated.

Natural variations of cold tolerance and temperature acclimation in Caenorhabditis elegans

Temperature is critical for the survival and proliferation of animals, which must be adapted to cope with environmental temperature changes. In this study, we demonstrated natural variations in the phenotypes of temperature tolerance and temperature acclimation of the nematode Caenorhabditis elegans, and we decoded whole genome sequence of six natural variations, which enabled us to map responsible gene polymorphisms onto specific chromosomal regions. The C. elegans laboratory strain, N2, survives at 2xa0°C after cultivation at 15xa0°C but is unable to survive at 2xa0°C after cultivation at 20 or 25xa0°C. This cultivation-temperature-dependent cold tolerance occurs within a few hours after the temperature shift and is termed cold acclimation. We measured the cold tolerance and cold acclimation phenotypes of many natural variants isolated from various areas. CB4854 showed weaker cold tolerance associated with gene polymorphisms on the sex chromosome decoded by whole genome sequencing. Variable cold acclimation phenotypes were exhibited in twelvexa0natural isolates and the large difference was seen between CB4856 and AB1 strains. CB4856, isolated from Hawaii, acclimated slowly to a new temperature, whereas AB1, isolated from Australia, acclimated rapidly. By the whole genome sequencing analysis, two different polymorphisms responsible for the accelerated cold acclimation in AB1 were mapped to specific chromosomal regions.

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.

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

Significance Environmental temperature acclimation is essential to animal survival, yet thermoregulation mechanisms remain poorly understood. In this study, we describe Ca2+-dependent endoribonuclease (EndoU) ENDU-2 located in ADL chemosensory neurons and specific muscle cells as a regulator of multiple pleiotropic phenomena including cold tolerance, life span, and brood size through cell-autonomous and cell-nonautonomous pathways in nematode Caenorhabditis elegans. Ca2+ imaging revealed ADL temperature response to be the result of transient receptor potential (TRP) channel activity and regulated by ENDU-2 via cell-autonomous and cell-nonautonomous pathways. Transcriptome analysis revealed that ENDU-2 influences expression of the caspase gene ced-3. Moreover, ENDU-2 downregulates cold tolerance and synaptic remodeling in the dorsal nerve cord through caspase signaling. We therefore propose a model for cold tolerance regulation that occurs via EndoU action. 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.