GFAP and neoplasm: The edges of the transcription network are given weights based on expression data such that expression data from a normal control group (N, optic nerves from Nf1flox/flox mice, which are equivalent to wild-type mice [2]), result in a “normal” network, while data from a group of optic glioma tumor samples (OPG-1, optic nerves from Nf1flox/null; GFAP-Cre mice, [2]) comprise a “tumor” network.