Promotion of mitosis in cultured newt limb regenerates by a diffusible nerve factor

Regeneration blastemata of adult newt forelimbs were cultured transfilter to dorsal root ganglia on extremely low porosity (0.05 mu m) filters. Mitotic index profiles in these blastemata were compared with those obtained using filters of greater porosity (0.45 mu m). In the above experiments nerves and blastema tissue were separated by 5 or 25 mu m, i.e., the thickness of the respective filters. The results show that the transfilter mitogenic effect of the nerves was retained when the lower pore size filters were used. In addition, sensory ganglia grown at the bottom of a culture well, separated from the blastema explants by a distance of approximately 2 mm, were nevertheless able to promote blastema cell proliferation. The ganglia can thus be considered to be providing a "sustained conditioning" of the medium with neuromitogenic factor(s). This study also shows that nerves can promote blastema cell mitosis, although cell-to-cell contact between nerves and responding cells was precluded.