Gap junctions in C. elegans

Abstract

As in other multicellular organisms, the nematode Caenorhabditis elegans uses gap junctions to provide direct cell-to-cell contact. The nematode gap junctions are formed by innexins (invertebrate analogs of the connexins); a family of proteins that surprisingly share no primary sequence homology, but do share structural and functional similarity with connexins. The model organism C. elegans contains 25 innexin genes and innexins are found in virtually all cell types and tissues. Additionally, many innexins have dynamic expression patterns during development, and several innexins are essential genes in the nematode. C. elegans is a popular invertebrate model due to several features including a simple anatomy, a complete cell lineage, sequenced genome and an array of genetic resources. Thus, the worm has potential to offer valuable insights into the various functions of gap junction mediated intercellular communication.

Hexadecameric structure of an invertebrate gap junction channel

“…This led to some extrapolation in the literature that innexin channels may also contain hexameric hemichannels and dodecameric junction channels like connexin [29][30][31][32]. On the other hand, it has also been reported that invertebrate gap junction channels are larger than vertebrate junction channels [12][13][14][15]20].…”

The electrical synapse: Molecular complexities at the gap and beyond

“…Although Cxs and Inxs share similar membrane topology and form similar intercellular structures their sequences are unrelated (Phelan, ; Oshima et al, ). To date, mammalian genomes encode approximately twenty Cx‐encoding genes whereas C. elegans and D. melanogaster genomes encode twenty five and eight Inx‐encoding genes, respectively (Phelan and Starich, ; Söhl et al, ; Simonsen et al, ). Currently, at least five Cxs (Cx30.2, Cx36, Cx45, Cx50, Cx57) are definitively known to be expressed within mammalian neurons, while five others (Cx29, Cx30, Cx32, Cx43, Cx47) are expressed exclusively in glia (Nagy et al, )—at least in mature circuits.…”

“…Currently, at least five Cxs (Cx30.2, Cx36, Cx45, Cx50, Cx57) are definitively known to be expressed within mammalian neurons, while five others (Cx29, Cx30, Cx32, Cx43, Cx47) are expressed exclusively in glia (Nagy et al, )—at least in mature circuits. Similarly, only a subset of Inxs are known to be expressed in invertebrate neurons (Simonsen et al, ). This diversity of Cx/Inx genes provides ample opportunity for complex GJ formation where each hemi‐channel could be created from multiple Cx/Inxs (heteromeric) or hemi‐channels created by different Cx/Inxs could couple between cells (heterotypic, discussed below).…”

The Caenorhabditis elegans INX‐4/Innexin is required for the fine‐tuning of temperature orientation in thermotaxis behavior

“…Innexins in invertebrates are considered to have similar topology and functional properties to those of connexins and pannexins in vertebrates (Barbe, Monyer, & Bruzzone, ; Beyer, & Berthoud, ; Phelan & Starich, ; Simonsen, Moerman, & Naus, ). Connexins and innexins are known to form gap junctions by docking of hemichannels in adjacent cells and implicated in exchange of ions and small signaling molecules between cells (Phelan, ; Söhl, Maxeiner, & Willecke, ).…”