Mushroom bodies in an ogre mutant
Figure legend: The photos above show cross-sections through the mushroom body (MB) pedunculus as indicated in the illustration on the left. Neuropile glial processes (green) are revealed by expression of UAS-mCD8:GFP under the transcriptional control of nrv2-GAL4 (Sun et al, 1999). Axons (seen in cross-section) of the pedunculus axonal tract have been stained for the presence of FasII (purple). Top left panel, Neuropile glial processes completely ensheath the pedunculus in wild type animals. Right panels, show pedunculus cross-sections from two different ogre mutant brains (Image: ogre mutant genotype). The glial sheath is abnormal, or missing, and clusters of neurons appear to separate from the main axonal tract, or possibly, different sub-populations of MB neurons exhibit different levels of FasII staining unlike wild type MB neurons which all seem to express similar levels of FasII. The neuronal phenotype is most probably a consequence of glial loss. Ogre has not been detected in mushroom body neurons so they are unlikely to be directly effected in the ogre mutant. Bottom left panel, When UAS-ogre is expressed in glia under the transcriptional direction of nrv2-GAL4 in an ogre mutant, glial processes again ensheath the pedunculus and FasII staining resembles that seen in wild type animals.
Figure legend: Green colour in the mushroom body diagram on the left illustrates the area where serial optical sections were obtained in order to generate three-dimensional reconstructions of a section of pedunculus from wild type an ogre mutant brains. Upper sequence images, wild type. Glial processes almost entirely ensheath the pedunculus section (Image: animated 3D reconstruction - wild type). The right-most panel has the glial staining removed, leaving only the reconstructed pedunculus axonal tract (purple, FasII) which appears to have a 'smooth' exterior. Lower sequence images, Glial sheath is absent from much of the ogre mutant pedunculus, leaving the axonal tract exposed (Images: animated 3D reconstruction 1 - ogre mutant, animated 3D reconstruction 2 - ogre mutant). The outer surface of the ogre mutant axonal tract has a 'globular' morphology compared to the smooth surface of a fully ensheathed axonal tract (right-most panels). Defective axonal morphology is also apparent by examining mushroom body lobe structure in ogre mutants. Mushroom body neurons - purple, FasII. Ensheathing glia - green, nrv2-GAL4 / UAS-mCD8:GFP.
Figure legend: Innexin proteins have so far not been detected in mushroom body neurons. A, The upper three panels show a region of the third instar larval brain focusing on the mushroom body Kenyon cell bodies (KC) and the calyx. These neuronal structures (green, UAS-GFP/+;OK107-GAL4/+) do not contain Inx2 (purple) gap junction plaques. B, A close-up view of an adult mushroom body lobe structure (Image: Mushroom body structure). A Z-series projected image (left panel) shows Inx2 (red) plaques surrounding the α-lobe. A single optical section (right panel) reveals that these plaques are limited to glia at the periphery of the lobe. Inx2 is not found in mushroom body axons or cell bodies (also true for Ogre and Inx3 in larvae and adults) which suggests that the abnormalities observed in neuronal structures in ogre mutants are an indirect effect, secondary to glial defects.