Cartilage calcification and limb bud growth in the developing tich mouse embryo

The tich mutation leads to the abnormal development of bones in mice such that a 'V-shaped' tongue of noncalcified cartilage appears in the central portion of the proximal tibial growth plate. In this study, alcian green staining of cartilage glycosaminoglycans was used to demonstrate the pattern of limb development in embryos of stage-matched tich and normal, co-isogenic, A.TL mice from the earliest stages in skeletogenesis. The growth plates of normal A.TL siblings were symmetrical across the limb rudiment whereas the growth plate in tich siblings show the beginnings of a V-shaped tongue of cartilage reaching towards the diaphysis. This showed first at E16.5. It was apparent that the crown rump distance, tibia, ulna, and the length of calcified cartilage in tich were significantly shorter than A.TL. These results confirmed that calcification was not the primary defect in tich but point to a temporal dysfunction in growth factor expression (possibly bone morphogenetic proteins) that stems from early limb bud formation and translates through later stages in development.