Genetically Engineered Mouse Models of Gliomas: Technological Developments for Translational Discoveries

Abstract

The most common brain tumours, gliomas, have significant morbidity. Detailed biological and genetic understanding of these tumours is needed in order to devise effective, rational therapies. In an era generating unprecedented quantities of genomic sequencing data from human cancers, complementary methods of deciphering the underlying functional cancer genes and mechanisms are becoming even more important. Genetically engineered mouse models of gliomas have provided a platform for investigating the molecular underpinning of this complex disease, and new tools for such models are emerging that are enabling us to answer the most important questions in the field. Here, I discuss improvements to genome engineering technologies that have led to more faithful mouse models resembling human gliomas, including new cre/LoxP transgenic lines that allow more accurate cell targeting of genetic recombination, Sleeping Beauty and piggyBac transposons for the integration of transgenes and genetic screens, and CRISPR-cas9 for generating genetic knockout and functional screens. Applications of these technologies are providing novel insights into the functional genetic drivers of gliomagenesis, how these genes cooperate with one another, and the potential cells-of-origin of gliomas, knowledge of which is critical to the development of targeted treatments for patients in the clinic.

Keywords: CRISPR; cancer; glioma; mouse model; piggyBac; transposon.

Figure 1

(A) Summary of glioma subtypes, including oligodendroglioma, astrocytoma and glioblastoma (GBM). The transcriptional subtypes of GBM are based on large-scale transcriptomics of human GBMs [25]. (B) The genetic features of these glioma subtypes, with the typical mutations seen in each category. The diagnosis of glioma is currently based on integration of classical histopathology with defining mutations (World Health Organisation (WHO) criteria). ‘pHGG’ refers to pediatric high-grade glioma, which has a different spectrum of mutations compared with adult GBMs. Illustration was prepared using the Motifolio drawing toolkit.

Figure 2

The use of genetically engineered mouse models for investigating the cell of origin of glioblastomas. The appropriate Cre transgenic mouse line can be selected for investigating the role of neurons, astrocytes, oligodendrocytes, oligodendrocyte precursor cells (OPC) or neural stem cells. Conditional mice carrying mutations in the relevant tumor suppressor genes or oncogenes are crossed with the cre line to determine the effect of these mutations in transforming the cell of interest. The glioblastomas (GBMs) generated are subject to phenotyping (such as transcriptional and histopathological) to determine their relevance to the human disease. Such models are also invaluable for exploring the cooperativity between genes of interest in gliomagenesis.

Figure 3

Somatic mutagenesis using clustered regularly interspaced short palindromic repeats (CRISPR)-cas9 for developing glioma genetically-engineered mouse models (GEMMs). A new and efficient method for generating somatic gene knockout is by crossing a conditional-Cas9 transgenic mouse with the appropriate cre for recombination in the cells of interest. Lentiviral delivery of single guide RNAs (sgRNAs) through stereotaxic brain injections will lead to knockout of the gene of interest (eg Trp53) only in the cells expressing Cas9 where cre-mediated recombination has occurred.