Longitudinal bone-growth and growth-plate dynamics are altered in 2-week-old, but not mature, Stat5ab–/– mice. (a) Representative proximal tibial sections stained with toluidine blue from 2-, 6-, and 10-week-old wild-type and Stat5ab–/– mice. Horizontal bars indicate the limits of the proliferative (Prol) and hypertrophic (Hyp) zones. Scale bar, 100 μm. (b) Femoral length, femoral width, and widths of the proliferative and hypertrophic zones of the proximal tibial growth plate in wild-type and Stat5ab–/– mice at 2, 6, and 10 weeks of age; n = 6–12 per group. AP < 0.05, BP < 0.01 vs. control mice.