In vitro control of blastema cell proliferation by extracts from epidermal cap and mesenchyme of regenerating limbs of axolotls.

The presence of a mitogenic activity in limb blastemas of axolotls was detected in crude extracts of blastemas at the mid-bud stage. The mitogenicity of the extracts was estimated from the mitotic index of blastema cells grown for 6 days in the presence of limb blastema extracts, with colchicine present for the last 2 days. All the extracts tested (whole blastema, blastemal mesenchyme, epidermal cap) significantly enhanced proliferation of blastema cells. The highest stimulation factors we observed were 7 × with 7 μg protein/ml whole blastema extracts, 5.2 × with 14 μg/ml blastemal mesenchyme extracts, and 11 x with 3.5 μg/ml epidermal cap extracts. Hence the epidermal cap extracts appeared to be the most mitogenic. Extracts from the blastemal mesenchyme, although less mitogenic than the epidermal cap extracts, were more potent than nerve extracts [Albert P, Boilly B (1986) Biol Cell 58:251-262]. These results are discussed with regard to the production of growth factors during limb regeneration.