Stage- and region-dependent responses of chick wing-bud mesenchymal cells to retinoic acid in serum-free microcultures.

Abstract

Retinoic acid (RA) has been shown to affect skeletal patterning in vivo in both developing and regenerating limbs. Regional differences in RA concentrations alone cannot account for the region-specific cell behaviors involved in limb-skeletal morphogenesis. The present study explores a role for regional differences in signal interpretation in RA's effects along the anteroposterior and proximodistal axes of stage 21-22 and 23-24 chick wing-buds. Mesenchymal cells isolated from specific limb regions were grown in chemically defined medium and exposed to 5 or 50 ng/ml of RA for 4 days in high-density microtiter cultures. Previous studies showed that RA's effects on chondrogenesis and growth in such cultures differed depending on the position along the limb's proximodistal axis from which the cells were isolated. The present study is the first to show that such differences in RA-responsiveness also exist along the limb's anteroposterior axis, especially in the distal subridge mesenchyme. The region-dependent relationships between RA's effects on growth and chondrogenesis suggest that RA affects these two behaviors through different mechanisms. The regional differences in the responsiveness of these cells to exogenous RA are discussed with respect to their correspondence to the in vivo patterns of expression of RA-binding proteins, RA-receptors, and other patterning-related genes.