Palumbos, S. | bioRxiv Science

bioRxiv2019

Epidermal Growth Factor signaling acts directly and through a sedation neuron to depolarizes a sleep-active neuron following cellular stress

Sleep is induced by sleep-active neurons that depolarize at sleep onset to inhibit wake circuits. Sleep-active neurons are under the control of homeostatic and allostatic mechanisms that determine sleep need. However, little is known about the molecular and circuit mechanisms that translate sleep need into the depolarization of sleep-active neurons. During many conditions in C. elegans sleep induction requires a sleep-active neuron called RIS. Here, we defined the transcriptome of RIS to discover that genes of the Epidermal Growth Factor Receptor (EGFR) signaling pathway are expressed in RIS. With cellular stress, EGFR activates RIS, and RIS induces sleep. Activation of EGFR signaling in the ALA neuron has previously been suggested to promote sleep independently of RIS. Unexpectedly, we found that ALA activation promotes RIS depolarization. Our results suggest that ALA is a sedating neuron with two separable functions. (1) It inhibits specific wakefulness behaviors independently of RIS, (2) and it activates RIS to induce sleep. Whereas ALA plays a strong role in surviving cellular stress, surprisingly, RIS does not. In summary, EGFR signaling can induce sleep-active neuron depolarization by an indirect mechanism through activation of the sedating ALA neuron that acts upstream of the sleep-active RIS neuron as well as through a direct mechanism using EGFR signaling in RIS. Sedation rather than sleep appears to be important for increasing survival following cellular stress, suggesting that sedation and sleep play different roles in restoring health.\n\nHighlights- The transcriptome of the sleep-active RIS neuron reveals the presence of the EGFR signaling machinery\n- EGFR activates RIS directly upon cellular stress to induce sleep bouts\n- In parallel, EGFR activates RIS indirectly through the sedating ALA neuron\n- Sedation rather than sleep bouts support survival following cellular stress

neuroscience↗

bioRxiv2019

Dendritic spines on GABAergic neurons respond to cholinergic signaling in the Caenorhabditis elegans motor circuit.

Dendritic spines are specialized postsynaptic structures that detect and integrate presynaptic signals. The shape and number of dendritic spines are regulated by neural activity and correlated with learning and memory. Most studies of spine function have focused on the mammalian nervous system. However, spine-like protrusions have been previously reported in invertebrates, suggesting that the experimental advantages of smaller model organisms could be exploited to study the biology of dendritic spines. Here, we document the presence of dendritic spines in Caenorhabditis elegans motor neurons. We used super-resolution microscopy, electron microscopy, live-cell imaging and genetic manipulation to show that GABAergic motor neurons display functional dendritic spines. Our analysis revealed salient features of dendritic spines: (1) A key role for the actin cytoskeleton in spine morphogenesis; (2) Postsynaptic receptor complexes at the tips of spines in close proximity to presynaptic active zones; (3) Localized postsynaptic calcium transients evoked by presynaptic activity; (4) The presence of endoplasmic reticulum and ribosomes; (5) The regulation of spine density by presynaptic activity. These studies provide a solid foundation for a new experimental paradigm that exploits the power of C. elegans genetics and live-cell imaging for fundamental studies of dendritic spine morphogenesis and function.\n\nHIGHLIGHTS- Spines in C. elegans GABAergic motor neurons are enriched in actin cytoskeleton.\n- Spines are dynamic structures.\n- Spines display Ca++ transients coupled with presynaptic activation.\n- Spine density is regulated during development and is modulated by actin dynamics and cholinergic signaling.

neuroscience↗