Fig. 3. Effects of N-Myc deficiency on the size and pattern of the limb skeleton. (A) Alcian Blue (staining for cartilage) and Alizarin Red (staining for bone) staining of PC and PC-NMyc^f/f mouse embryos at E15.5. (B) E15.5 autopods stained with Alcian Blue. Note that the phalangeal elements of digit 1 (thumb, black arrows) are longer in PC-NMyc^f/f embryos and resemble those of the most posterior digit (digit 5 or little finger). (C) The distal skeleton of E18.5 PC and PC-NMyc^f/f embryos stained with Alcian Blue and Alizarin Red. Note the lack of well-defined joints (black arrows), or absence of joints, in the digits of PC-NMyc^f/f embryos. Note also the bony fusions that occur at the base of the anterior and posterior digits of the PC-NMyc^f/f autopod (red arrows). (D) Analysis of Sox9 expression, a marker of cartilage growth and development, by whole-mount and section in situ hybridization at the indicated embryonic stages. (E) Whole-mount in situ hybridization showing Noggin expression at E11.5. (F) Expression of Gdf5, a marker of joint development, at the indicated embryonic stages.