Upregulated Hedgehog Signaling Promotes Zebrafish CNS Tumorigenesis

Using a cytokeratin 5 gene promoter, we ectopically expressed a constitutively active zebrafish smoothened (smoa1) in presumably glial progenitor cells of zebrafish CNS. Stable transgenic zebrafish developed retinal tumors and low grade glioma of the optic nerve. Microarray analysis showed upregulation of Hh downstream targets of ptc1, gli1 and gli2a in tumors. Immunofluorescence studies confirmed overexpression of Pax2, GFAP, S100 and Sox2, specifically in gliomas. We also detected upregulated expression of phosphorylated pRb and Mdm2 associated with gliomagenesis. Our results suggest that dysregulated Hh signaling initiates tumorigenesis in zebrafish CNS. Zebrafish optic nerve maintains phosphorylated pRb expression, therefore provides a unique niche for pathogenesis of glioma. RNAs from 4 gross eye tumors (from fish of 4 months of age) and 4 normal eyes from wil-type control fish were extracted and used for array analysis