PMC

(A–C) Activity of Msx2-cre persisted in the ventral forelimb ectoderm and inter-limb flank from E10.5 to E11.5. (D, E, G and H) Compared with E10.5, ectopic expression of Fgf8 in the ventral forelimb ectoderm was significantly reduced at E11.5 (red arrowheads). (F and I) Ectopic expression of Fgf8 disappeared along the inter-limb flank.

(A–F) The expression of ectopic Fgf8 was observed in the head, inter-limb flank, and tail regions at E10.5 (red arrowheads). (G–L) The expression of Shh was also detected in these extra tissues at E11.5 (red arrowheads). (M–R) The expression of Msx1 was observed in the extra tissues at the lateral flank, head, and tail regions at E12.5 (black arrowheads). (S–V) Only extra limbs immediately adjacent to the forelimb showed normal pattern identity, as reflected by the expression of Hoxd13 and Hoxa11 (green arrowheads), marking the autopod and zeugopod regions of the limb bud, respectively.

(A and E) Ectopic tissues were observed above the eyes in the mutants (yellow arrows). (B and F) An extra limb was formed immediately posterior to the forelimb (yellow arrow). (C and G) Ectopic outgrowths appeared in the abdominal region (yellow arrow). (D and H) The mutants showed saw-like tails due to the formation of ectopic tissues on the tail surface (yellow arrowheads).

(A and C) a whole-mount view of the abdomen revealed that in severely affected Msx2-cre; β-catenin^Δex3 mutants, AVBW closure had not been completed at E16.5, at which stage the AVBW of normal littermates has already closed at the abdominal midline (black arrowheads). (B and D) Sagittal view of the abdominal center. Yellow arrowheads indicate the intestines. (E–H) At E14.5, when obvious umbilical ring structures were present in the abdomen of normal embryos, the AVBW was closed in severely affected Msx2-cre; β-catenin mutants (black arrowheads), as revealed by the enclosure of the intestines by the body wall (F and H). Green arrowheads indicate the body wall.