Fig. 2. Co-expression of Sox5 and Sox6 in the notochord and nucleus pulposus. Mid-sagittal and cross-sections were made in the lumbar vertebral column of E11.5-E15.5 wild-type embryos. Cross-sections were chosen in intervertebral regions. Each row shows pictures of adjacent sections. Left-hand panels are sections stained with Alcian Blue and nuclear Fast Red to identify the neural tube (NT), notochord (arrows), intervertebral mesenchyme (IM), inner annulus (IA), outer annulus (OA), nucleus pulposus (NP) and vertebral bodies (VB). The other panels show Sox5 (middle) and Sox6 (right) RNA in situ hybridization (arrows indicate notochord). The second row displays high-magnification pictures of the boxed areas in the first row. The left-hand pictures for each hybridization were photographed under standard conditions of blue fluorescence (cell nuclei) and dark-field exposure (RNA signals). Fluorescence only was used for the right-hand pictures to visualize the notochord better. At all stages, Sox5 and Sox6 are co-expressed in the notochord, nucleus pulposus, prechondrocytes (IM) and chondroblasts (IA, VB). The signal for Sox5 RNA is slightly weaker in the notochord and nucleus pulposus than in surrounding tissues, whereas the signal for Sox6 RNA is similar is all these tissues.