The effect of cytochalasin B on chondrogenesis in chick limb-bud mesoderm cells grown in vitro

Summary Cytochalasin B (CB) has been shown to have many biological effects on cultured cells. We report that an initial 48-hr treatment of freshly plated chick embryo limb mesoderm cells with CB irreversibly inhibits chondrogenesis. A slight inhibition in the amount of matrix is seen when limb cells are allowed to grow in culture for 24 hr prior to treatment for the second 24 hr of culture. If the cells are allowed to plate-out and grow for 48 hr or longer prior to being treated with CB for 24 hr, the amount of matrix produced is essentially the same as that seen in the controls. However, if the initial 48-hr culture period is followed by a 48- or 72-hr treatment, chondrogenesis is reduced, but not to the same extent as that seen in cultures treated for the first 48 or 72 hr. The irreversible inhibition of chrondrogenesis does not appear to be due to irreversible inhibition of protein synthesis or hexose uptake because, although these are reduced during treatment, they return to control levels within 48 hr following the removal of the drug. We cannot mimic the effect of CB treatment using glucose-deficient medium, thereby eliminating the possiblity that a critical glucose level is necessary to permit chondrogenesis. Multinucleation of limb cells treated with CB is reversed within 4 to 7 days following the removal of the drug. Therefore multinucleation alone is probably not responsible for the CB effect on chondrogenesis. However, other subtle permanent changes may occur during the period of multinucleation which result in the irreversible inhibition of chondrogenesis. This work was supported in part by a grant to R. A. F. from the North Carolina United Way and a grant to C. L. P. from the General Research Support Grant RR-5404 from the National Institutes of Health. A portion of these results were presented at the 28th Annual Meeting of the Tissue Culture Association, New Orleans, Louisiana, 1977.