Evolution of gap junctions: the missing link?
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Amino Acid Sequence↗
Biomedical subjects
Jane A Davies
Publications and source records attributed to Jane A Davies.
Molecular basis of gap junctional communication in the CNS of the leech Hirudo medicinalis.
Gap junctions are intercellular channels that allow the passage of ions and small molecules between cells. In the nervous system, gap junctions mediate electrical coupling between neurons. Despite sharing a common topology and similar physiology, two unrelated gap junction protein families exist in the animal kingdom. Vertebrate gap junctions are formed by members of the connexin family, whereas invertebrate gap junctions are composed of innexin proteins. Here we report the cloning of two innexins from the leech Hirudo medicinalis. These innexins show a differential expression in the leech CNS: Hm-inx1 is expressed by every neuron in the CNS but not in glia, whereas Hm-inx2 is expressed in glia but not neurons. Heterologous expression in the paired Xenopus oocyte system demonstrated that both innexins are able to form functional homotypic gap junctions. Hm-inx1 forms channels that are not strongly gated. In contrast, Hm-inx2 forms channels that are highly voltage-dependent; these channels demonstrate properties resembling those of a double rectifier. In addition, Hm-inx1 and Hm-inx2 are able to cooperate to form heterotypic gap junctions in Xenopus oocytes. The behavior of these channels is primarily that predicted from the properties of the constituent hemichannels but also demonstrates evidence of an interaction between the two. This work represents the first demonstration of a functional gap junction protein from a Lophotrochozoan animal and supports the hypothesis that connexin-based communication is restricted to the deuterostome clade.
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Cloning and expression of a leech complexin.
Release of neurotransmitter from presynaptic nerve terminals is mediated by SNARE proteins, which are located on the vesicle and plasma membranes. These proteins form a SNARE complex thought to mediate membrane fusion. Complexin is a soluble protein essential for transmitter release, which has been postulated to bind to and stabilise the SNARE complex. We have cloned a complexin homologue, Hm-cpx1, from the leech, Hirudo medicinalis. This protein is expressed in only a subset of neurons in the leech CNS, including the Retzius and P neurons. It is 33% identical to rat complexin I, and 44% identical to squid complexin. Sequence conservation is particularly high in the predicted SNARE binding domain.
Amino Acid Sequence↗
Gap junctions in Drosophila: developmental expression of the entire innexin gene family.
Invertebrate gap junctions are composed of proteins called innexins and eight innexin encoding loci have been identified in the now complete genome sequence of Drosophila melanogaster. The intercellular channels formed by these proteins are multimeric and previous studies have shown that, in a heterologous expression system, homo- and hetero-oligomeric channels can form, each combination possessing different gating characteristics. Here we demonstrate that the innexins exhibit complex overlapping expression patterns during oogenesis, embryogenesis, imaginal wing disc development and central nervous system development and show that only certain combinations of innexin oligomerization are possible in vivo. This work forms an essential basis for future studies of innexin interactions in Drosophila and outlines the potential extent of gap-junction involvement in development.
Amino Acid Sequence↗