Innexin Gap Junctions

Innexins in glia ensheathing the mushroom body neuronal tract

Image showing Inx2 protein in a single section through the mushroom body glial sheath

Figure legend: Optical cross-sections through the mushroom body pedunculus reveal Inx2 plaques (red) in the neuropile glial processes (green) that ensheath the pedunculus axonal tract. Inx2 is detected using a rabbit polyclonal Inx2-specific antibody. Neuropile glia are revealed by the glial reporter nrv2-GAL4 / UAS-mCD8:GFP (Sun et al, 1999). The Inx2 staining pattern is almost identical to that seen for Ogre and Inx3 (not shown) and is found all along the length of the pedunculus. Some glial processes pass through the pedunculus, possibly segregating axonal clusters on the basis of neurotransmitter (Strausfeld et al. 2003).

Image showing a 3D reconstruction of part of the mushroom body glial sheath containing Inx2 plaques

Figure legend: A three-dimensional reconstruction of a section of the neuropile glia that ensheath the pedunculus (Image: 3D animation of Inx2 in glial tube). Glia form an almost continuous tubular corridor through which mushroom body axons pass on their way from the Kenyon cell bodies (Kcb) to the lobes (Image: 3D animation of glial processes ensheathing a section of pedunculus axonal tract). Large Inx2 plaques (red) are abundantly distributed throughout the sheath. Where Inx2 (red) and glia (green) co-localise the merged colour appears yellow. Although many plaques appear red, that is a side-effect of rendering the 3D image - less intense GFP fluorescence is removed during the process - making many of the Inx2 plaques seem 'naked'. What is the role of all these plaques in this structure?

  • - adhesion of glial processes?
  • - maintenance of glia that are required for normal mushroom body neuronal development eg. axonal pathfinding (Freeman, 2006)?
  • - do they have a glial-specific role that is required for normal mushroom body neuronal function? For example, removal of neurotransmitters to prevent them from accummulating to toxic levels (Rival et al. 2004)? It has been reported that gap junctional communication is important for glial glutamate transporter expression in vertebrates (Figiel et al, 2007)
  • - 'spatial buffering' - removal of ions from areas of high neuronal activity to prevent toxic build-up (Wallraff et al. 2006)?

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