Loss of ensheathing glia from the mushroom body pedunculus neuronal tract in an ogre mutant.
In wild type animals neuropile glial processes almost completely ensheath the mushroom body (MB) pedunculus tract of Kenyon cell axons (Glia ensheathing the pedunculus in a wild type animal)(Scanned region of pedunculus). The abundance and morphology of ensheathing glial processes is drastically reduced in ogre mutant animals (Constructing an adult viable ogre genotype), as seen in the image above (green - glia; purple - mushroom body axons, FasII). The axonal tract is completely unsheathed and the shape of the axonal tract is globular and disorganised. The phenotype is quite variable...another example is shown here at the same magnification. Whether the loss of glia is due to a defect during glial cell proliferation or a maintenance problem later on (Ogre protein is expressed in these glia in the adult and may perform a function essential for normal structure/survival) is currently unknown. The axonal tract defect may be caused indirectly due to the loss of ensheathing glia. We detected no Ogre protein in wild type mushroom body neurons in adults or larvae. When UAS-ogre is expressed in the mutant glial cells under the control of nrv2GAL4 (Sun et al, 1999) the ensheathment and axonal tract phenotypes are rescued (Comparison of mutant and rescued ogre brains)...although rescue of some phenotypes is only partial, for example, optic lobe size becomes almost normal but their internal structure remains disrupted (Rescue of ogre mutant optic lobes) and mushroom body βγ lobes occasionally fuse across the midline (Comparison of mutant and rescued ogre brains).