Fig. 7. Expression patterns of cartilage differentiation markers in mid-gestation embryos. (A) Pattern of Ihh expression in E12.5 control embryo detected by whole-mount in situ hybridization. Arrow indicates Ihh expression in the radius and ulna condensations of the forelimb bud. (B) Double mutant embryo with forelimb bud at approximately the same limb bud stage as that of control embryo in A stained with Ihh probe. Note significantly lower level of Ihh expression in radius and ulna (arrow) compared with control. (C) Ihh transcription in stage 12 control radius and ulna. (D) In situ hybridization of Ihh probe to section of a double mutant stage 12 forelimb. Transcripts are abundant in digit elements, but absent from radius and ulna. (E) Pthlh transcripts are found in the perichondrium surrounding carpal elements and the distal ends of the radius and ulna in E15.5 wild-type embryos. (F) Although Pthlh expression in the carpal region is readily observed in Hoxa11/Hoxd11 double mutant embryos, expression extending proximally around the distal radius and ulna is not seen. (G) In situ hybridization of the parathyroid hormone receptor (Pthr) probe to section of a stage 10 control embryo. (H) Section of a stage 12 double mutant forelimb hybridized with the Pthr probe. Transcripts are present in the digits but undetectable in the radius or the ulna. (I) Expression pattern of Hoxd11 in a stage 9-10 wild-type forelimb detected by in situ hybridization using a ³³P-labeled probe. Hoxd11 transcripts surround the ulna, with high levels at the distal end, and also surround the radius, carpals and digit condensations at this stage (data not shown). (J) Hoxa11 transcripts, detected by a ³³P-labeled probe, are abundant in mesenchyme surrounding the radius and ulna.