Fig. 11.

Bone vasculature serves as a template for mineral deposition. The involvement of vascular patterning in bone morphogenesis. Vascular patterning in the bone precedes and predicts mineral deposition sites. At E14.5, blood vessels are asymmetrically distributed. At E15.5, mineral distribution follows the vascular pattern of the previous day. Whereas blood vessels outside the bone are covered with basement membrane (BM), inside the bone the vasculature lacks BM. Enlargements of the boxed areas are shown below. At E14.5, collagen I is seen on the bone collar and on adjacent blood vessels. At E15.5, mineral is deposited onto the collagen I-covered vessels, which exhibit a reduction in EC marker. On the right is an enlargement of the boxed area showing older mineral undergoing thickening. Osteoblasts secrete collagen I, which is deposited on the mineral from one side and, in small fragments, on the blood vessel on the other side.