Biology subjects

Liewald, J.

Publications and source records attributed to Liewald, J..

3 recordsLinked to original sources

bioRxiv2026

All-optical analysis of electrical coupling in muscle ensembles reveals contributions of individual innexins to cell synchronizationand locomotion

Gap junctions (GJs), formed by connexins in vertebrates and innexins in invertebrates, enable direct ion flow between adjacent cells. GJ coupling is typically analyzed by electrophysiological methods, which, however, are invasive and cannot be conducted in intact animals. Here, we used all-optical methods to non-invasively investigate electrical coupling in body wall muscle (BWM) cells of intact Caenorhabditis elegans. We analyzed the roles of specific innexins (unc-9, inx-11, inx-16) in BWMs, using the genetically encoded fluorescent voltage indicator QuasAr2 to assess spontaneous muscle activity. unc-9 mutants showed strongly reduced coupling and asynchronous activity, and this was accompanied by severe locomotion defects. Overexpression of the murine connexin Cx36 increased synchronization but disrupted locomotion. inx-16 mutants exhibited increased excitability of individual muscle cells, likely due to reduced leak currents, while inx-11 mutants displayed only moderate defects. Patch-clamp recordings confirmed altered action potentials and increased input resistance in inx-16 mutants. Additionally, we established a cell-specific optogenetic voltage clamp (cOVC) method, directly revealing changes in junctional conductance in live, non-dissected animals. In sum, our findings demonstrate that a balanced level of GJ coupling is essential for coordinated muscle activity and proper motor behavior. Significance statementCoordination of cells in muscular organs requires electrical coupling via intercellular channels termed gap junctions (GJs). How this coupling contributes to coordinated activity like locomotion in an intact animal is difficult to assess, since commonly used electrophysiological methods require dissection, and are incompatible with behavior. Here, we developed all-optical electrophysiology methods to study GJ coupling in live C. elegans. Different innexin mutants, as well as overexpression of mammalian connexin Cx36, induced different locomotion defects and, compared to wild type, were accompanied by more or less electrical coupling and synchronicity of individual muscle cells. Loss of some innexins caused the insulated muscle cells to be more excitable. Thus, GJ coupling is required for fine-tuning locomotion, and can be studied by voltage imaging.

cell biology↗

bioRxiv2024

Loss of neuropeptidergic regulation of cholinergic transmission induces CaV1-mediated homeostatic compensation in muscle cells

Chemical synaptic transmission at the neuromuscular junction (NMJ) is regulated by electrical activity of the motor circuit, but may also be affected by neuromodulation. Here, we assess the role of neuropeptide signaling in the plasticity of NMJ function in Caenorhabditis elegans. We show that the CAPS (Ca2+-dependent activator protein for secretion) ortholog UNC-31, which regulates the exocytosis of dense core vesicles (DCVs), affects both pre- and post-synaptic functional properties, as well as NMJ-mediated locomotion. Despite reduced evoked acetylcholine transmission, the loss of unc-31 results in a more vigorous response to presynaptic stimulation, i.e., enhanced muscle contraction and Ca2+ transients. Based on expression profiles, we identified neuropeptides involved in both cholinergic (FLP-6, NLP-9, NLP-21 and NLP-38) and GABAergic motor neurons (FLP-15, NLP-15), that mediate normal transmission at the NMJ. In the absence of these peptides, neurons fail to upregulate their transmitter output in response to increased cAMP signaling. We also identified proprotein convertases encoded by aex-5/kpc-3 and egl-3/kpc-2 that act synergistically to generate these neuropeptides. We propose that postsynaptic homeostatic scaling, mediated by increased muscle excitability, could compensate for the reduced cholinergic transmission in mutants affected for neuropeptide signaling, thus maintaining net synaptic strength. We show that in the absence of UNC-31 muscle excitability is modulated by upregulating the expression of the muscular L-type voltage gated Ca2+ channel EGL-19 (CaV1). Collectively, our results unveil a role for neuropeptidergic regulation in synaptic plasticity, linking changes in presynaptic transmission to compensatory changes in muscle excitability.

neuroscience↗

bioRxiv2022

Rapid and reversible optogenetic silencing of synaptic transmission by clustering of synaptic vesicles

Silencing neurons acutely and specifically informs about their functional roles in circuits and behavior. Existing optogenetic silencers include ion pumps or channels, and tools that damage the neurotransmitter release machinery. While the former hyperpolarize the cell and can alter ionic gradients, the latter allow only slow recovery, requiring de novo synthesis. Thus, there is a need for other strategies combining fast activation and reversibility. Here, we use light-evoked homo-oligomerization of cryptochrome CRY2 to silence synaptic transmission, by clustering synaptic vesicles (SVs). We benchmark this tool, optoSynC, by electrophysiology and locomotion in Caenorhabditis elegans. optoSynC clusters SVs within 25 s, causing approximation, observable by electron microscopy. Locomotion silencing is rapid (tauon [~]15 s) and recovers quickly (tauoff [~]10 min) after light-off. Further, optoSynC can inhibit exocytosis for several hours, at very low light intensities. optoSynC is a highly efficient, non-ionic optogenetic silencer that may further allow to manipulate different SV pools.

neuroscience↗