ABSTRACT
While depolarization of the neuronal membrane is known to evoke the neurotransmitter release from synaptic vesicles, hyperpolarization is regarded as a resting state of chemical neurotransmission. Here, we report that hyperpolarizing neurons can actively signal neural information by employing undocked hemichannels. We show that UNC-7, a member of the innexin family in Caenorhabditis elegans, functions as a hemichannel in thermosensory neurons and transmits temperature information from the thermosensory neurons to their postsynaptic interneurons. By monitoring neural activities in freely behaving animals, we find that hyperpolarizing thermosensory neurons inhibit the activity of the interneurons and that UNC-7 hemichannels regulate this process. UNC-7 is required to control thermotaxis behavior and functions independently of synaptic vesicle exocytosis. Our findings suggest that innexin hemichannels mediate neurotransmission from hyperpolarizing neurons in a manner that is distinct from the synaptic transmission, expanding the way of neural circuitry operations.
Subject(s)
Caenorhabditis elegans Proteins , Caenorhabditis elegans , Neurons , Synaptic Transmission , Animals , Caenorhabditis elegans/metabolism , Caenorhabditis elegans Proteins/metabolism , Caenorhabditis elegans Proteins/genetics , Connexins/metabolism , Connexins/genetics , Interneurons/metabolism , Membrane Proteins , Neurons/metabolism , Synaptic Transmission/physiology , Synaptic Vesicles/metabolism , Taxis Response/physiologyABSTRACT
Animals integrate sensory stimuli presented at the past and present, assess the changes in their surroundings and navigate themselves toward preferred environment. Identifying the neural mechanisms of such sensory integration is pivotal to understand how the nervous system generates perception and behavior. Previous studies on thermotaxis behavior of Caenorhabditis elegans suggested that a single thermosensory neuron AFD plays an important role in integrating the past and present temperature information and is essential for the neural computation that drives the animal toward the preferred temperature region. However, the molecular mechanisms by which AFD executes this neural function remained elusive. Here we report multiple forward genetic screens to identify genes required for thermotaxis. We reveal that kin-4, which encodes the C. elegans homolog of microtubule-associated serine threonine kinase, plays dual roles in thermotaxis and can promote both cryophilic and thermophilic drives. We also uncover that a thermophilic defect of mutants for mec-2, which encodes a C. elegans homolog of stomatin, can be suppressed by a loss-of-function mutation in the gene crh-1, encoding a C. elegans homolog CREB transcription factor. Expression of crh-1 in AFD restored the crh-1-dependent suppression of the mec-2 thermotaxis phenotype, indicating that crh-1 can function in AFD to regulate thermotaxis. Calcium imaging analysis from freely moving animals suggest that mec-2 and crh-1 regulate the neuronal activity of the AIY interneuron, a postsynaptic partner of the AFD neuron. Our results suggest that a stomatin family protein can control the dynamics of neural circuitry through the CREB-dependent transcriptional regulation within a sensory neuron.
Subject(s)
Caenorhabditis elegans Proteins , Taxis Response , Animals , Caenorhabditis elegans/metabolism , Protein Serine-Threonine Kinases/genetics , Caenorhabditis elegans Proteins/genetics , Caenorhabditis elegans Proteins/metabolism , Sensory Receptor Cells/metabolism , Temperature , Microtubules/metabolism , Behavior, Animal/physiology , Transcription Factors/metabolismABSTRACT
Animals detect changes in both their environment and their internal state and modify their behavior accordingly. Yet, it remains largely to be clarified how information of environment and internal state is integrated and how such integrated information modifies behavior. Well-fed C. elegans migrates to past cultivation temperature on a thermal gradient, which is disrupted when animals are starved. We recently reported that the neuronal activities synchronize between a thermosensory neuron AFD and an interneuron AIY, which is directly downstream of AFD, in well-fed animals, while this synchrony is disrupted in starved animals. However, it remained to be determined whether the disruption of the synchrony is derived from modulation of the transmitter release from AFD or from the modification of reception or signal transduction in AIY. By performing forward genetics on a transition of thermotaxis behavior along starvation, we revealed that OLA-1, an Obg-like ATPase, functions in AFD to promote disruption of AFD-AIY synchrony and behavioral transition. Our results suggest that the information of hunger is delivered to the AFD thermosensory neuron and gates transmitter release from AFD to disrupt thermotaxis, thereby shedding light onto a mechanism for the integration of environmental and internal state to modulate behavior.