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Fig. 2. Mesenchyme determines the timing of intramembranous ossification.
(A) In quck mandibles, quail mesenchyme maintains its faster timetable
for bone formation within the slower environment of duck hosts, based on
histological detection of matrix (arrow) using Osteoid stain (blue).
(B) Staining for bone is coincident only with Q¢PN positive cells
(i.e. quail-derived black cells, arrow) on the donor side. (C)
Reciprocal transplants that generate duail result in abundant quail
host-derived bone in chimeric mandibles (arrow). (D) On the duck
donor-derived side, bone has yet to form at 6 days of culture (dashed
outline). Note the sporadic Q¢PN-positive angioblasts and endothelial
cells, which are derived from quail host mesoderm, among duck donor mesenchyme
(Q¢PN-negative). (E,F) After 8 days of culture, which is
equivalent to the time required for bone to form in control duck, duck-derived
mesenchyme (i.e. Q¢PN-negative) stains positively (dashed outline).
(G,H) Whole-mount in situ hybridization reveals that
Runx2 and Msx1 are upregulated on the donor-derived
side.
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