Figure 2: Rescue of Pitx1−/− HL skeletal defects by Tbx4 but not Tbx5.

(a) Lateral view of e17.5 skeletal preparations (alcian blue/alizarin red staining of cartilage and bone, respectively) showing lower spine and HL of Pitx1+/− (identical to Pitx1+/+), Pitx1−/− and transgene rescues. (b) Angle of pelvis (dotted outline) relative to spine. The increased angle observed in Tbx5 transgenics (column 4) was quantitated (± s.e.m.) in embryos showing displacement (n=5/5). FL scapula (dotted line) relative to spine angle in column 5. (c) Loss of ilium (il) in Pitx1−/− (column 2) embryos and anterior HL displacement with femur head aligned (dotted line) with sacral vertebra S1 rather than S3 (column 1). Complete rescue of ilium and HL position in 8 of 10 (partial in 2) Tbx4 transgenic mice (column 3), but not in Tbx5 transgenic mice (n=5/5). Is, ischium. (d) Limb joints for indicated limb and genotype. (e) Schematic of bone contacts, with green line between fibula (Fb)/tibia (Ti) in Pitx1+/− and Pitx1−/−;Prx1-Tbx4 HL and magenta between ulna (Ul)/humerus (Hum) in FL or mutant fibula/femur (Fe) in Pitx1−/− mutant and Pitx1−/−;Prx1-Tbx5 HL. Rescue of normal HL contacts in 5 of 10 Tbx4 transgenic skeletons examined (column 3), but not in Tbx5 (n=5/5). (f) Angle (black line) between calcaneus and footplate in HL or between pisiform and handplate in FL. Angle (± s.e.m.) measured for the number (n) of rescued embryos as indicated. (g) Femur length (± s.e.m.) for indicated genotypes and number (n) of embryos examined. Pitx1−/− femurs develop a tuberosity (asterisk, columns 2 and 4) that is similar to humerus deltoid tuberosity (DT, column 5).