The accumulation of basement membrane components during the onset of chondrogenesis and myogenesis in the chick wing bud.

The study describes the distribution of several basement membrane molecules in the embryonic chick wing bud from stages 23 to 26, during the onset of myogenesis and chondrogenesis, and then later at stage 28. Laminin is localized as early as stage 23, prior to the onset of myogenesis, in regions corresponding to the position of the future dorsal and ventral myogenic areas. Other matrix components, including fibronectin, do not differentially accumulate in these same regions. Fibronectin, basement membrane heparan sulphate proteoglycan and type IV collagen are more widespread in their distribution than laminin, and are even present between mesenchymal cells. These results suggest a role for laminin in the initial differentiation of the muscle masses and emphasize that components of basement membrane can also be associated with mesenchymal cells.