MATRIX CHANGES DURING LONG-TERM CULTIVATION OF CARTILAGE (ORGANOID ORHIGH-DENSITY CULTURES)

In high density (organoid or micromass) cultures of prechondrogenic me senchymal cells from limb buds of 12-day-old mouse embryos typical car tilaginous tissue develops after 3 days. Immunomorphological investiga tions have shown that it contains the typical components of the cartil aginous matrix, such as collagen type II and cartilage-specific proteo glycans. After a 2-week cultivation period hypertrophic cartilage cell s develop to an increasing extent. Many of these cells as well as norm al chondroblasts detach from the matrix from the 2nd week in vitro onw ards to assume a fibroblast-like appearance. At the same time thick (2 5-65 nm) collagenous fibrils occur at the surface of these cells. Thes e thick fibrils contain collagen type I, as shown by immunomorphology. Hence, in these older cartilage cultures chondroblasts change their s ynthesis programme or direction of differentiation. Consequently, a mo del for the study of <<dedifferentiation>> of cartilage and possibly a lso transformation of cartilage cells to osteoblasts has become availa ble.