We next tested whether Ptdsr is functionally required for the clearance of apoptotic cells. We started with an investigation of cell death in vivo in the interdigital areas of the developing limbs. Apoptosis of interdigital cells in the distal mesenchyme of limb buds occurs most prominently from developmental stages E12.0 to E13.5 and can be easily examined in situ by whole-mount terminal deoxynucleotide transferase-mediated UTP end-labeling (TUNEL). We compared the pattern of interdigital cell death in fore and hind limb buds from Ptdsr -/- (n = 3) and Ptdsr +/+ (n = 3) mice at E12.5 and E13.5. No differences in accumulation of TUNEL-positive cell corpses were observed between the two genotypes (Figure 6a). The kinetics of cell death occurrence and regression of the interdigital web was similar in wild-type and mutant littermates, providing no evidence that Ptdsr-deficiency is associated with impaired clearance of apoptotic interdigital cells during limb development.