Innexin Gap Junctions

Inx2 and Ogre co-localise in brain glia

Image showing Drosophila Inx2 and Ogre-myc proteins occupying the same position within glia

Figure legend: A single optical section through the mushroom body pedunculus. The section is taken from approximately halfway between the calyx and the lobes (Image: Structure of the mushroom bodies), as illustrated on the left. Endogenous Inx2 plaques (red) are detected using rabbit polyclonal Inx2-specific antibodies. The plaques are not present in the axonal tract of the pedunculus, instead they are found in neuropile glial processes that ensheath the axonal tract (Image: Inx2 plaques in the pedunculus glial corridor). The neuropile glia cells express transgenic myc-tagged Ogre protein (purple) under the transcriptional control of the nrv2-GAL4 enhancer trap line (Sun et al, 1999). Co-antibody staining for Inx2 and myc reveals that both proteins generally aggregate in the same regions of glial processes (arrowheads) suggesting that these subunits might exist in the same plaques, perhaps even forming channels together. Ogre subunits alone cannot form functional homomeric channels in the heterologous Xenopus oocyte system (Phelan and Starich, 2001) so it is likely that they must interact with other innexin subunits to form channels in vivo. Inx2 and Ogre (...and Inx3...) also co-localise in other tissues (Lehmann et al, 2006)(see Inx family members interact). It is known from studies of connexins that gap junction subunits that are co-expressed within the same cells do not necessarily form channels together. For instance, Cx29 and Cx32 are both expressed in myelinating Schwann cells but occupy distinct membrane locations (Altevogt et al, 2002) and the two connexins Cx43 and Cx26 are observed to co-localise at plaques in cell culture but occupy separate sub-domains within these plaques (Gemel et al. 2004). Examination of Drosophila cells that express multiple members of the innexin protein family also reveals that different subunits can occupy separate, discrete, plasma membrane regions (eg. Inx2 is predominantly apico-lateral whilst Ogre is baso-lateral in embryonic hindgut epithelial cells (Bauer et al, 2004) and Ogre and Zpg/Inx4 occupy opposite ends of follicle cells (Bohrmann and Zimmermann, 2008)(Image: Innexin distribution in the follicle).

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