Fig. 4. BMP4 inhibits oligodendrocyte development without significantly affecting astrocyte development. E4 spinal cord flat mounts were organ cultured in control conditions (A,C,F) or treated (B,D,G) with 0.6 nM BMP4. In all micrographs, broken lines delineate the floor plate area. (A,B) Transverse sections from spinal cords grown for 2 days, stained with O4 antibody. In control spinal cords, oligodendrocyte precursors are found in the ventral neuroepithelium, close to the floor plate (arrows in A). BMP4 treatment alone totally abolishes the emergence of O4-positive cells (B). (C-G) Transverse sections from spinal cords grown for 8 days and stained with antibodies directed against GFAp (C,D) or PLP/DM20 (F,G). In control sections, numerous astrocytes (C) and oligodendrocytes (F) are observed, with higher density at the lateral edge of the flat mount. BMP4 treatment alone abolishes oligodendrocyte development (G) but does not appear to modify the pattern of expression of GFAp (D). (E) Quantification of the area covered by GFAp immunoreactive material in control or BMP4 treated spinal cord flat mounts, expressed in percent of total section surface.