Hideto Koso1,2, Asano Tsuhako1, Eli Lyons1, Jerrold M. Ward2, Alistair G. Rust3, David J. Adams3, Nancy A. Jenkins2,4, Neal G. Copeland2,4,*, and Sumiko Watanabe1,*
1 Division of Molecular and Developmental Biology, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan
2 Division of Genetics and Genomics, Institute of Molecular and Cell Biology,
Agency for Science, Technology and Research, Singapore, Singapore
3 Experimental Cancer Genetics, Wellcome Trust Sanger Institute,
Hinxton, Cambridge, United Kingdom
4 Cancer Research Program, The Methodist Hospital Research Institute, Houston, Texas
* Corresponding authors
Published in Cancer Research on 15 April 2014.
Medulloblastoma is the most common pediatric brain tumor, and in approximately 25% of cases, it is driven by aberrant activation of the Sonic Hedgehog (SHH) pathway in granule neuron precursor (GNP) cells. In this study, we identified novel medulloblastoma driver genes through a transposon mutagenesis screen in the developing brain of wild-type and Trp53 mutant mice. Twenty-six candidates were identified along with established driver genes
such as Gli1 and Crebbp. The transcription factor FoxR2, the most frequent gene identified in the screen, is overexpressed in a small subset of human medulloblastoma of the SHH subtype. Tgif2 and Alx4, 2 new putative oncogenes identified in the screen, are strongly expressed in the SHH subtype of human medulloblastoma. Mutations in these two genes were mutually exclusive with mutations in Gli1 and tended to co-occur,
consistent with involvement in the SHH pathway. Notably, Foxr2, Tgif2, and Alx4 activated Gli-binding sites in co-operation with Gli1, strengthening evidence that they function in SHH signaling. In support of an oncogenic function, Foxr2 overexpression transformed NIH3T3 cells and promoted proliferation of GNPs, the latter of which was also observed for Tgif2 and Alx4. These findings offer forward genetic and functional evidence associating Foxr2, Tgif2, and Alx4 with SHH subtype medulloblastoma.
Figure Legend: Transposon mutagenesis induces medulloblastoma.
A: Kaplan-Meier survival curves show that mice with mobilized transposons display shortened survival compared with mice without mobilized transposons.
B: Tumors were found in the cerebellum (arrows).
C-E, H&E: Staining of tumors show classic histologic features of medulloblastomas. Arrows, multinucleated giant cells. Bars, 100 mm.
F and G: Tumors were negative for GFAP (F, left) and Nestin (G, left). GFAP and Nestin
staining were observed in cortical astrocytes (F, right) and the ventricular zone of embryonic brain (G, right), respectively. Bars, 100 mm.
H: PCR-based detection of the recombined and activated Trp53R172H mutant allele. The Trp53R172H mutant allele was detected in the cerebellum (Ce) of double transgenic animals (Nes-cre/þ; Trp53R172H/þ) but not in control (Ctrl) animals (Trp53R172H/þ). Both Trp53 WT and Trp53R172H mutant alleles were observed in 6 MBs (T1-T6).