Fig. 3.

Administration of IPTG can induce regeneration defects in an animal with a LacI-dependent transgene. Scale bar in all images is 1 mm in length. (A) Right hind limb from O-Tsp4; CAG-LacI F₀ transgenic animal reared in the absence of IPTG shows a normal morphology. (B) Following amputation and subsequent housing in IPTG, the same limb regenerated with several defects including truncated posterior digits, missing digit 2, and a bifurcation on another digit (arrowhead). (C) When placed immediately into water without IPTG following the amputation of the limb shown in B, an almost entirely normal limb regenerated. (D) Skeletal preparation of the limb shown in B revealed the bifurcated minidigit contained a cartilaginous condensation (arrowhead); additionally, long bones in the stylopod and zeugopod regrew with a nodule near the center (asterisk). (E) Skeletal preparation of the limb shown in C demonstrated that even a malformed, IPTG-induced limb can regenerate an almost perfect limb in the absence of IPTG (normal skeletal morphology, missing one posterior digit). (F) The same limb was amputated again and allowed to regenerate in the absence of IPTG, producing a morphologically perfect limb.