Is abnormal limb bud morphology in the mutant Talpid² chick embryo a result of altered intercellular adhesion? Studies employing cell sorting and fragment fusion

In the past, studies of avian limb morphogenesis emphasized epithelial‐mesenchymal tissue interactions and problems of determination of limb symmetry. In contrast, a recent hypothesis, based on studies of the aggregation rates of dissociated cells and on computer modeling, proposes that the paddle shaped polydactylous limb of the talpid³ mutant is the result of increased intercellular adhesion of limb bud mesoderm cells during limb development. The notion that differences in intercellular adhesion may have profound effects on limb morphogenesis has not been critically explored previously. The present experimental approach includes studies of cell sorting in aggregates containing both talpid² and wild‐type cells. In this system, adhesive differences should result in cell sorting. Instead, cell sorting did not occur, indicating by this test at least, that limb bud mesoderm cells of talpid² and wild‐type embryos are equally adhesive. This conclusion finds support from studies involving tissue spreading in fused fragments of talpid² and wild‐type limb bud mesenchyme tissue and in studies of kinetics of aggregation of dissociated cells.