FIG. 4.

Cell proliferation in prehypertrophic chondrocytes in costal joints. Pregnant mice were injected with bromodeoxyuridine and sacrificed, and embryos were collected at day 16.5. BrdU incorporation was determined immunohistochemically, and the percentage of positive cells was plotted. Only littermates were used for comparisons; in one litter a single pair of p107⁻/⁻ and p107^−/− p27^D51/D51 was obtained, and in another litter two p107⁻/⁻ animals were paired with a single p107^−/− p27^D51/D51 sibling. Each tick mark represents the percentage of cells in one section that were BrdU positive. p107⁻/⁻, 3,5797 cells counted; p107^−/− p27^D51/D51, 2,7743 cells counted.