Developmental progression of the transgenic phenotype in the vertebral column. (A-H) Alizarin red and alcian blue stained wild-type and transgenic lumbar vertebrae, ventral view. (A, B) E12.5 reveals no differences between wild-type and transgenic embryos. (D) At E13.5 presumptive IVDs stain with alcian blue in transgenic embryos (arrowhead) but not in (C) wild-types. At E14.5 (E) vertebrae of wild-type embryos are separated by weaker stained IVDs (arrowhead). The notochord is extruded to the nucleus pulposus. (F) Transgenic vertebrae are shortened, stain uniformly with alcian blue, IVDs are missing and the notochord remains as a rod like structure. Newborn transgenic mice (H) exhibit two lateral centres of ossification compared to one centre in wild-type mice (G). ivd, intervertebral disc; L, lumbar vertebra; nc, notochord; np, nucleus pulposus; s, somite; T, thoracic vertebra; TG, transgenic mouse; vb, vertebral body; WT, wild-type.