Chondrogenesis in the mutant nanomelia. Changes in the fine structure and proteoglycan synthesis in high density limb bud cell cultures.

High density limb bud micromass cultures, derived from individual four-day embryos, were established in order to examine chondrogenesis in normal and nanomelic embryos. One- and three-day cultures revealed no morphological differences between the two genotypes. At six days in culture, the scalloping of the cell surface observed in normal chondrocytes is not extensive in the mutant, and the extracellular matrix granules are greatly reduced in number. Differences in sulfated proteoglycan (PGS) synthesis were first detected at three days in culture when the mutant failed to synthesize cartilage-specific PGS. The study, therefore, indicates that the mutant gene is not expressed in prechondrogenic cells.