Fig. 1. dri is not expressed in midline-derived cells of the Drosophila embryonic CNS. Confocal micrographs of stage 15 whole-mount embryos carrying specific enhancer trap lines directing ß-galactosidase expression in midline cells of the CNS. Embryos were immunochemically stained with polyclonal rabbit anti-ß-gal (Alexa488-conjugated secondary antibody, green) and rat anti-DRI (Lissamine-Rhodamine-conjugated secondary antibody, red). Anterior is towards the left. Some dri-positive cells are located in the vicinity of the embryonic midline: (A) Posterior to the posterior commissures (arrow) as revealed by the mAb 22C10 axonal marker; (B) posterior to X55-positive cells (the VUM neurones, the MNB and its support cells and the posterior pair of the midline glia) (arrow); (C) posterior to Star-positive (P 2333) midline glia (long arrow); and (D) half way between neighbouring segmental clusters of AA142-positive midline glia (MGA, MGM and MGP) (long arrow). There is one dri-positive cell per hemineurome located at the very edge of the VNC (A-D, notched arrowhead), posterior to the intersegmental nerve root as revealed by the mAb 22C10 (A). Other dri-positive CNS cells are labelled with short arrows in C-D.