GRADED EXPRESSION OF EMX-2 IN THE ADULT NEWT LIMB AND ITS CORRESPONDING REGENERATION BLASTEMA

Amputation of a newt Limb causes stump cells to organize the reformati on of the missing structures. The phenomenon is remarkably precise in that the regeneration is perfect. During the first few days following amputation, the tissue proximal to the plane of amputation gives rise to the blastema, an area of growth composed of mesenchymal cells cover ed by a single epithelium. The blastema possesses a morphogenetic pote ntial characteristic of the structures that have been amputated. Looki ng for control genes putatively involved in regeneration, we cloned th e newt version of the mouse and human Emx-2. Its expression is restric ted to the skin of the regeneration territories and is graded along th e proximal-distal axis of both forelimb and hindlimb, with higher leve ls in distal regions. The regeneration blastema also show this proxima l-distal graded level of expression with distal blastemas (mid-radius and ulna) showing higher levels of expression when compared to blastem as of more proximal origin (mid-humerus). Finally, retinoic acid proxi malizes both the level of Emx-2 expression and the positional memory o f the blastema suggesting Emx-2 may participate in pattern formation b y specifying positional information. (C) 1998 Academic Press Limited.