Molecular characterization and embryonic expression of innexins in the leech Hirudo medicinalis

Abstract

Gap junctions are direct intercellular channels that permit the passage of ions and small signaling molecules. The temporal and spatial regulation of gap junctional communication is, thus, one mechanism by which cell interactions, and hence cell properties and cell fate, may be regulated during development. The nervous system of the leech, Hirudo medicinalis, is a particularly advantageous system in which to study developmental mechanisms involving gap junctions because interactions between identified cells may be studied in vivo in both the embryo and the adult. As in most invertebrates, gap junctions in the leech are composed of innexin proteins, which are distantly related to the vertebrate pannexins and are encoded by a multi-gene family. We have cloned ten novel leech innexins and describe the expression of these, plus two other previously reported members of this gene family, in the leech embryo between embryonic days 6 and 12, a period during which the main features of the central nervous system are established. Four innexins are expressed in neurons and two in glia, while several innexins are expressed in the excretory, circulatory, and reproductive organs. Of particular interest is Hm-inx6, whose expression appears to be restricted to the characterized S cell and two other neurons putatively identified as presynaptic to this cell. Two other innexins also show highly restricted expressions in neurons and may be developmentally regulated.

The Expression of Tubulin and Tektin Genes in Dicyemid Mesozoans (Phylum: Dicyemida)

“…Several, organ-specific innexin genes were reported in a leech, H. medicinalis (Dykes and Macagno, 2006), in Drosophila melanogaster (Drosophilidae) (Stebbings et al, 2002), and in C. elegans (Starich et al, 2003;Chuang et al, 2007;Whitten and Miller, 2007). In embryonic stages, they were exclusively expressed in germ layers, but the dicyemid innexin was expressed in all blastomeres of developing embryos after the 24-cell stage.…”

“…Indels in innexin amino acid sequence in 19 lophotrochozoan innexins of molluscs, annelids, brachiopods, platyhelminths, dicyemids, and 10 ecdysozoan innexin sequence of arthropods and nematodes. TM2 indicates location of the second trans-membrane domain deduced by Dykes et al (2004). Indel 1 and indel 2 indicate locations of specific indels.…”

“…Deduced amino acid sequences of the dicyemid innexin show their full lengths. TM indicates the locations of trans-membrane domains deduced by Dykes et al (2004). Boxes indicate conserved sequences in each taxa.…”

What is hidden in the pannexin treasure trove: the sneak peek and the guesswork

“…The growing body of recent sequence data from different organisms largely supports these conclusions. Indeed, no connexins were found among animals outside Chordata and more innexins were discovered in various Metazoans [16,18]. However, some complications to this simple description started to emerge.…”

In Situ Characterization of a Rectifying Electrical Junction

“…In the leech, 12 different innexin genes have been cloned and their products are thought to mediate electrical coupling between leech neurons (Dykes and Macagno 2005). The majority of the neurons expresses the same innexin, inx1, but few neurons express in addition another two innexins, inx6 and inx8.…”