Caenorhabditis elegansInnexins Regulate Active Zone Differentiation

Abstract

In a genetic screen for active zone defective mutants in Caenorhabditis elegans, we isolated a loss-of-function allele of unc-7, a gene encoding an innexin/pannexin family gap junction protein. Innexin UNC-7 regulates the size and distribution of active zones at C. elegans neuromuscular junctions. Loss-of-function mutations in another innexin, UNC-9, cause similar active zone defects as unc-7 mutants. In addition to presumptive gap junction localizations, both UNC-7 and UNC-9 are also localized perisynaptically throughout development and required in presynaptic neurons to regulate active zone differentiation. Our mosaic analyses, electron microscopy, as well as expression studies suggest a novel and likely nonjunctional role of specific innexins in active zone differentiation in addition to gap junction formations.

Mechanosensitive unpaired innexin channels in C. elegans touch neurons

“…Also, innexins have been experimentally shown to have gap junction-unrelated functions. For example, C. elegans innexin unc-7 functions cell autonomously to promote the development of the active zones in GABAergic motoneurons (76). Furthermore, unc-7 functions with the NCA cation leak channel to modulate neuronal activity, and this activity is independent from gap junction formation (10).…”

Oligomeric Structure and Functional Characterization of Caenorhabditis elegans Innexin-6 Gap Junction Protein

“…Studies using electron tomography estimated both the periodicity of the channels and the extracellular gap size between the junction membranes isolated from the lateral giant fibers of crayfish (23). Although the native gap junctions in C. elegans have been observed by thin-section EM (24,25), the molecular structure of innexin channels remains poorly resolved.…”

Filling the gap: adding super-resolution to array tomography for correlated ultrastructural and molecular identification of electrical synapses at theC. elegansconnectome

“…21 The C. elegans strain used for the gap junction study was ZM1158, which contains an outcrossed integrated array lwIs48[Punc-7:: UNC-7S::GFP], where an innexin UNC-7S fused with GFP was expressed from an endogenous unc-7 promoter. 22,23 UNC-7S appears to be the major form of UNC-7, 22 and for simplicity is referred to as UNC-7 in the main text. For dSTORM analyses, N2 Bristol wild-type was used.…”

“…To visualize a defined subset of neuronal gap junctions with srAT, we chose a transgenic line that expresses a functional UNC-7::GFP fusion from the native unc-7 promoter. 22,23 The UNC-7 innexin 16 is expressed in many neurons and some body wall muscles. 22 We used an antibody against GFP to stain for UNC-7::GFP, and co-stained for microtubules using an antibody against α-tubulin on ultrathin sections from the young adult C. elegans hermaphrodite.…”

“…Several identified gap junctions include those between AVK and SMBD, between AVK and RIG, between RIH and FLP, between AVK and ADE, and between RIM and RIS. These neurons have been previously identified to express UNC-7, 22,23 and on the basis of ultrastructure these gap junctions have been reported in the original C. elegans wiring diagram. 13 In addition, an unambiguous UNC-7::GFP labeled gap junction between ADA and ADF neurons was identified, which, to our knowledge, was not previously reported to express UNC-7.…”