ABSTRACT
Importance of limb tissue associations in the development of nerve-induced supernumerary limbs in the newt Pleurodeles waltlii Michah.
Brachial nerve tip deviation has been carried out at various points in the upper arm and close to the limb. Some associations of cutaneous or muscular tissue from two opposite sides - dorsal and ventral or anterior and posterior - of the upper arm were made at these points. Various degrees of development of the nerve-induced supernumerary limbs were observed. When a nerve deviation was not followed by grafting of tissue from the opposite side, the supernumerary limbs did not develop or were strongly hypomorphic. A normal limb development can occur when tissues from the opposite side are associated with the ones located at the nerve tip. Such associations allow a harmonious nerve-induced supernumerary limb to develop and consequently allow all transverse axes to be established. Orientation of nerve-induced supernumerary limbs is determined by the orientation of the tissues in the area of nerve deviation.
In terms of positional information, since an absence of contact between tissues from two opposite sides results in a lack of normal development, we can conclude that positional values located on either side of, the centre of, at least, one transverse axis should be in contact to allow limb development, i.e. a regenerated limb or nerve-induced supernumerary limbs or supernumerary limbs. It appears that contact between such values along any transverse axis, under sufficient nervous stimulation may give rise to a supernumerary limb.
