Developmental expression and molecular characterization of two gap junction channel proteins expressed during embryogenesis in the grasshopper Schistocerca americana

Gap junctions are membrane channels that directly connect the cytoplasm of neighboring cells, allowing the exchange of ions and small molecules. Two a nalogous families of proteins, the connex ins and innexins, are the channel -forming molecules in vertebrates and invertebrates, respectively. In order to study the role of gap junctions in the embryonic development of the ner vous system, we searched for innexins in the grasshopper Schistocerca ameri cana. Here we present the molecular cloning and sequence analysis of two no vel innexins, G-lnx(1) and G-lnx(2) expressed during grasshopper embryonic development. The analysis of G-lnx(1) and G-lnx(2) proteins suggests they b ear four transmembrane domains, which show strong conservation in members o f the innexin family. The study of the phylogenetic relationships between m embers of the innexin family and the new grasshopper proteins suggests that G-lnx(Il is orthologous io the Drosophila 1(1)-ogre. However, G-lnx(2) see ms to be a member of a new group of insect innexins. We used in situ hybrid ization with the G-lnx(1) and G-lnx(2) cDNA clones, and two polyclonal sera raised against different regions of G-lnx(1) io study the mRNA and protein expression patterns and the subcellular localization of the grasshop per i nnexins. Glnx(Tl is primarily expressed in the embryonic nervous system, in neural precursors and glial cells. In addition, a restricted stripe of epi thelial cells in the developing limb, involved in the guidance of sensory g rowth cones, expresses G-lnx(1). G-lnx(2) expression is more widespread in the grasshopper embryo, but a restricted expression is found in a subset of neural precursors. The generally different but partially overlapping expre ssion patterns of G-lnx(1) and G-lnx(2) supports the combinatorial characte r of gap junction formation in invertebrates, an essential property io gene rate specificity in this form of cell-cell communication. (C) 1999 Wiley-Li ss, Inc.