NERVE EXTRACTS AND SUBSTANCE-P ACTIVATE THE PHOSPHATIDYLINOSITOL SIGNALING PATHWAY AND MITOGENESIS IN NEWT FORELIMB REGENERATES

We investigated the inositol phospholipid transmembrane signaling path way as a possible mediator of neurotrophic (mitogenic) signals in the newt limb regeneration blastema. Blastema mesoderm tissues were prelab eled with myo-[H-3] inositol, treated with 10 mM LiCl and then exposed to substance P or to extracts of spinal ganglia, brain, or spinal cor d. Stimulation with substance P resulted in a rapid dose-dependent red uction of [H-3]phosphatidylinositol 4,5-bisphosphate and [H-3]phosphat idylinositol 4-phosphate, correlated with a rapid accumulation of inos itol 1,4,5-triphosphate. This effect was inhibited when the blastema t issue was treated with neomycin, a known inhibitor of inositol phospho lipid turnover. In addition, substance P stimulated the incorporation of [H-3]thymidine into DNA of blastema mesoderm cells, and this effect was also suppressed by neomycin, at a dose corresponding to that requ ired to inhibit inositol phosphate accumulation. Extracts of neural ti ssues, especially spinal ganglia, induced the formation of inositol ph osphates and extract activity was attenuated following treatment with heat or trypsin. These findings suggest a role for mitogen-activated i nositol phospholipid signaling, initiating events that ultimately lead to cell proliferation. (C) 1995 Academic Press, Inc.