Fig. 1. Targeted misexpression of gcm results in gain of glial cells at the expense of neuronal cells. (A,B) In situ hybridization of stage 10 embryos shows gcm expression in wild-type (A) and in sca-gcm embryos (B); lateral views, anterior towards the left. In the wild type, small clusters of cells in the neuroectoderm express gcm; in sca-gcm embryos, all cells of the neuroectoderm express gcm. (C,D) Immunostaining with anti-REPO in wild-type (C) and in sca-gcm (D) embryos; laser confocal microscopy of stage 11, ventral views of the VNC, anterior is towards the left. In the wild-type, single gcm-expressing glial precursors in each hemisegment express the repo gene. In sca-gcm embryos, virtually all of the neuronal and glial precursor cells are REPO positive. (E,F) Double immunostaining with anti-REPO (green) and anti-HRP (red) in wild-type (E) and in sca-gcm (F) embryos; laser confocal microscopy of stage 15/16 embryos. In the wild type, neurons and glial cells are differentiated and correctly positioned, and all lateral glial cells express repo. In sca-gcm embryos, 80%-90% of the cells in the CNS express repo.