2020

EN2

-;engrailed homeobox 2;EN2;engrailed homeobox 2

engrailed homolog 2|engrailed-2|homeobox protein en-2|homeobox protein engrailed-2|hu-En-2

7q36

protein-coding

Pilocytic astrocytomas (PAs) are the most common brain tumors in pediatric patients and can cause significant morbidity, including chronic neurological deficiencies. They are characterized by activating alterations in the mitogen-activated protein kinase pathway, but little else is known about their development. To map the global DNA methylation profiles of these tumors, we analyzed 62 PAs and 7 normal cerebellum samples using Illumina 450K microarrays.These data revealed two subgroups of PA that separate according to tumor location (infratentorial versus supratentorial), and identified key neural developmental genes that are differentially methylated between the two groups, including NR2E1and EN2. Integration with transcriptome microarray data highlighted significant expression differences, which were unexpectedly associated with a strong positive correlation between methylation and expression. Differentially methylated probeswere often identified within the gene body and/or regions up- or downstream of the gene, rather than at the transcription start site. We also identified a large number of differentially methylated genes between cerebellar PAs and normal cerebellum, which were again enriched for developmental genes. In addition, we found a significant association between differentially methylated genes and SUZ12 binding sites, indicating potential disruption of the polycomb repressor complex2 (PRC2). Taken together, these data suggest that PA from different locations inthe brain may arise from region-specific cells of origin, and highlight the potential disruption of key developmental regulators during tumorigenesis. Thesefindings have implications for future basic research and clinical trials, as therapeutic targets and drug sensitivity may differ according to tumor location.

Medulloblatoma is a pediatric brain tumor originating in the human cerebellum. Acollection of 23 medulloblastomas was analyzed for expression of the developmental control genes of the PAX and EN gene families by RNase protection and in situ hybridization. Of ALL nine PAX genes investigated, only PAX5 and PAX6 were consistently expressed in most medulloblastomas (70 and 78% of ALL cases, respectively), as were the genes EN1 (57%) and EN2 (78%). EN1, EN2, and PAX6 genes were also expressed in normal cerebellar tissue, and their expression in medulloblastoma is consistent with the hypothesis that this tumor originates in the external granular layer of the developing cerebellum. PAX5 transcripts were,however, not detected in the neonatal cerebellum, indicating that this gene is deregulated in medulloblastoma. In the desmoplastic variant of medulloblastoma, PAX5 expression was restricted to the reticulin-producing proliferating tumor areas containing undifferentiated cells; PAX5 was not expressed in the reticulin-free nonproliferating islands undergoing neuronal differentiation. These data suggest that deregulated expression of PAX5 correlates positively with cell proliferation and inversely with neuronal differentiation in desmoplastic medulloblastoma.