Figure 4

BrdU incorporation in Hoxc-8 transgenic animals. Incorporation of BrdU in Hoxc-8 transgenic animals was detected by Horseradish Peroxidase (HRP) immunohistochemistry on sections from embryonic day 15.75 animals. Sections were cut at 5 μm thickness and counterstained with Hematoxylin. Quantitation of BrdU incorporation was obtained by counting cells in the vertebral centers on multiple sections from the same individual (see Methods). Panel A: Cartilage of the humerus (50 × magnification). Panel B: Cartilage of the third rib (200 ×). Panel C: Cartilage of the sixth rib (400 ×). Panel D: Hypertrophic cells of the scapula (200 ×). BrdU incorporation was only detected in proliferating and prehypertrophic, but not in hypertrophic cells. Panel E: BrdU incorporation (dark colored bars) in vertebral center chondrocytes (light colored bars: cells without BrdU incorporation) of embryos at embryonic day 15.5 to 16.5. Data were obtained from animals with moderate (blue; genotype TA/+ TR/+) and high (red; genotype TA/TA TR/+) Hoxc-8 expression. Panel F: Fraction of cells labeled by BrdU incorporation as a function of size of vertebral centers in animals with moderate (blue, open symbol) and high (red, closed symbol) Hoxc-8 transgene expression levels (genotypes correspond to colors as before).