Gap Junctions and NCA Cation Channels Are Critical for Developmentally Timed Sleep and Arousal in Caenorhabditis elegans

Abstract

<p class="first" id="d277667e257">The molecular mechanisms of sleep are not fully understood. Huang <i>et al.</i> demonstrate that loss of <i>Caenorhabditis elegans</i> UNC-7 or UNC-9 innexins dramatically reduces sleep during L4/A lethargus and that those innexins are partially required... </p><p class="first" id="d277667e266">An essential characteristic of sleep is heightened arousal threshold, with decreased behavioral response to external stimuli. The molecular and cellular mechanisms underlying arousal threshold changes during sleep are not fully understood. We report that loss of <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00006747;class=Gene" id="d277667e268" target="xrefwindow">UNC-7</a> or <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00006749;class=Gene" id="d277667e271" target="xrefwindow">UNC-9</a> innexin function dramatically reduced sleep and decreased arousal threshold during developmentally timed sleep in <i>Caenorhabditis</i> <i>elegans</i>. <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00006747;class=Gene" id="d277667e280" target="xrefwindow">UNC-7</a> function was required in premotor interneurons and <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00006749;class=Gene" id="d277667e284" target="xrefwindow">UNC-9</a> function was required in motor neurons in this paradigm. Simultaneous transient overexpression of <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00006747;class=Gene" id="d277667e287" target="xrefwindow">UNC-7</a> and <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00006749;class=Gene" id="d277667e290" target="xrefwindow">UNC-9</a> was sufficient to induce anachronistic sleep in adult animals. Moreover, loss of <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00006747;class=Gene" id="d277667e293" target="xrefwindow">UNC-7</a> or <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00006749;class=Gene" id="d277667e296" target="xrefwindow">UNC-9</a> suppressed the increased sleep of <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00001173;class=Gene" id="d277667e299" target="xrefwindow">EGL-4</a> gain-of-function animals, which have increased cyclic-GMP–dependent protein kinase activity. These results suggest <i>C. elegans</i> gap junctions may act downstream of previously identified sleep regulators. In other paradigms, the NCA cation channels act upstream of gap junctions. Consistent with this, diminished NCA channel activity in <i>C. elegans</i> robustly increased arousal thresholds during sleep bouts in L4-to-adult developmentally timed sleep. Total time in sleep bouts was only modestly increased in animals lacking NCA channel auxiliary subunit <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00006811;class=Gene" id="d277667e309" target="xrefwindow">UNC-79</a>, whereas increased channel activity dramatically decreased sleep. Loss of <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00001173;class=Gene" id="d277667e312" target="xrefwindow">EGL-4</a> or innexin proteins suppressed <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00006811;class=Gene" id="d277667e315" target="xrefwindow">UNC-79</a> loss-of-function sleep and arousal defects. In <i>Drosophila</i>, the ion channel narrow abdomen, an ortholog of the <i>C. elegans</i> NCA channels, drive the pigment dispersing factor (PDF) neuropeptide release, regulating circadian behavior. However, in <i>C. elegans</i>, we found that loss of the PDF receptor <a data-untrusted="" href="http://www.wormbase.org/db/get?name=WBGene00015735;class=Gene" id="d277667e328" target="xrefwindow">PDFR-1</a> did not suppress gain-of-function sleep defects, suggesting an alternative downstream pathway. This study emphasizes the conservation and importance of neuronal activity modulation during sleep, and unequivocally demonstrates that gap junction function is critical for normal sleep. </p>