Determination of limb bud chondrocytes during a transient block of the cell cycle

The process of determination is studied by using a cell culture system derived from dissociated chick embryo limb buds. When limb bud cells obtained from embryos younger than stage 25 (undertermined) are temporarily prevented from passing through the cell cycle (either by maintaining the cells on a petri dish or in the presence of high concentrations of cyclic AMP, both of which depress thymidine-H(3) incorporation), some cells subsequently form cartilage colonies. These results support the hypothesis that a temporary block at some stage in the cell cycle causes mesoblasts to acquire the capacity to differentiate into cartilage cells.