Is retinoic acid essential for patterning during axolotl limb regeneration

Retinoic acid (RA) has been detected in the regenerating limb, and exogenous RA can proximalize, posteriorize, and ventralize blastemal cells. Thus RA may be an endogenous regulatory factor during limb regeneration. Retinoic acid receptors (RAR) form heterodimers with retinoic X receptors (RXR) and transactivate RAR/RXR responsive genes. This thesis examined whether endogenous RA is essential for patterning during axolotl (Ambystoma mexicanum) limb regeneration, by using retinoid antagonists that bind to specific RAR or RXR subtypes. Retinoid antagonists: Ro41-5253, Ro61-8431, LE135, and LE540 were implanted into the regenerating limb using silastin blocks. The skeletal pattern of regenerated limbs treated with Ro41-5253 or Ro61-8431 differed only slightly from control limbs. LE135 inhibited limb regeneration, and LE540 revealed relatively normal regenerated limbs. Implanting LE135 and LE540 together, regeneration was not completely inhibited: a hand-like process regenerated. These results demonstrate a possible role of endogenous RA during patterning of the regenerating limb.