Proximodistal leg regeneration in Carausius morosus: growth, intercalation and proximalization

The proximodistal epidermal organization of the regenerated insect leg has been studied by grafting between corresponding and noncorresponding levels of the pro- and metathoracic femur and tibia. The results have been studied quantitatively (growth rates of the associated parts and of unsegmented intercalary structures) and qualitatively (nature, length, polarity of intercalary structures). In grafts between equivalent levels, no intercalary structure is formed, but a differential growth has been observed, the distal one fifth of segments growing about 1.5 to 2 times more than the proximal one. In grafts between different levels, unsegmented intercalary structures are formed from the distal part which thereby acquires proximal characteristics (proximalization). However, distal tibial cells do not form femur in this process under an hypothetical femoral influence: there is no 'dominance' of femur over tibia. Some segmented intercalary structures have also been observed, but their formation cannot be related clearly to differences in the healing process. To explain proximalization, an hypothesis is presented suggesting that distal cells, which grow faster, would be the first to enter a period when positional value becomes labile and would then adapt to the proximal cells' value.

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