[P81]: Semaphorin signalling during glioma cell migration and tumor progression

Neurofibromatosis type 1 (NF1) predisposes to benign, incurable peripheral nerve tumors. We hypothesized that expansion of a progenitor population in Nf1 mutant peripheral nerves contributes to tumorigenesis. To test this hypothesis, we studied progenitor cells from Nf1 mutant mice. We identified an embryonic dorsal root ganglia (DRG) derived cell population, which is expandable as EGF-dependent self-renewing spheres; loss of Nf1 is associated with an increase in sphere formation. Spheres from both wild type and Nf1 mutant DRG contained cells capable of glial differentiation. Spheres from Nf1 mutants contained cells with increased propensity to form neurons in vitro when compared with wild type cells. An EGFR+;p75+ cell population was previously isolated from Nf1 DRG cultures; here we show that these cells (Nf1−/−TXF) can be propagated as spheres at greatly (20×) increased efficiency. Consistent with a progenitor phenotype, Nf1−/−TXF cells showed migratory characteristics of neural crest stem cells in a chicken xenograft model and expressed markers (as assessed using Affymetrix GeneChips) of neural crest and at least three crest derivatives: neurons, Schwann cells, and melanocytes. Knockout of Nf1 at the embryonic Schwann cell stage of development, but not earlier or later, generated this progenitor like population, implying that loss of Nf1 at a critical stage in development causes an expansion of progenitor cells. Nf1 but not wild type perinatal mouse nerves contained cells expressing EGFR and p75, suggesting abnormal persistence of the progenitor population. We also prospectively identified EGFR+;p75+ cells by FACS analysis of human neurofibromas, and have derived spheres from primary neurofibroma cells in the presence of EGF. These data support the hypothesis that an EGFR+ neural progenitor is amplified in Nf1 mutants and is relevant to peripheral nerve tumorigenesis in NF1.