Fig. 4. Supplementation of Hoxa13 homozygous mutant limbs with BMP2 or BMP7 partially restores interdigital programmed cell death (IPCD) and Msx2 expression. (A-C) Hoxa13 heterozygotes exhibited elevated levels of IPCD when treated with beads soaked in 0.1 mg/ml rhBMP2 or rhBMP7, whereas PBS control beads did not elevate IPCD beyond normal levels in organ cultured limbs. (D-F) IPCD is partially restored in Hoxa13 homozygous mutants in the presence of rhBMP2- or rhBMP7-treated beads, whereas PBS-treated beads did not re-initiate IPCD. Arrows denote sites of IPCD as detected by TUNEL assay (red signal). (G-J) Organ cultures of Hoxa13 mutant limbs treated with rhBMP2 or rhBMP7 exhibit reduced levels of Msx2 induction (arrows), when compared with age-matched controls. (K,L) Control treatments using PBS-beads had no affect on Msx2 expression (arrows). Roman numerals denote digits II, III and IV. Scale bar: 50 µm.