Intrinsic control of vascularization in developing cartilage rudiments.

The vascularization of developing cartilage rudiments is temporally and spatially defined. By using an in vivo angiogenesis model, the chorioallantoic membrane (CAM) of the chick embryo and chick embryo cartilage rudiments, we conclude that the factors controlling the vascular invasion of cartilage rudiments are intrinsic. Intact rudiments, separate hypertrophic zones and separate rounded cell zones, when grafted onto the CAM, become vascularized in the same temporal and spatial manner as occurs in ovo. When grown as organ cultures prior to CAM grafting, rudiments still become vascularized in the same temporal and spatial manner. The integrity of the extracellular matrix and the presence of the periosteum are two physical factors regulating the control of vascularization. Removal of the periosteum from hypertrophic regions caused a cessation of the invasion. Insults to the matrix via brief enzymatic degradation of extracellular matrix components resulted in invasion and erosion of rounded cell zones at an earlier time than is ordinarily seen both in ovo and on the CAM.