Development of Transgenic and Allograft Mouse Models of Ependymoma

Despite brain tumours being the leading cause of cancer death in children and ependymoma being the third most common pediatric brain tumour, its pathogenesis remains poorly understood and treatment options are limited to surgical resection with adjunct radiation. Ependymoma research has been severely hampered by the lack of in vitro and in vivo models. Using both transgenic and allograft approaches, this research aimed to establish mouse model(s) of this disease by applying putative ependymoma-initiating genetic events onto RGCs that are recognized as its cells of origin. We observed that transgenic mice with constitutive Notch signaling in their RGCs showed predisposition to ependymoma through development of SVZ hyperplasia in their lateral ventricles. We further promoted tumourigenesis by activating the SB transposon-based insertional mutagenesis system, which resulted in higher incidence of more aggressive ependymoma-like SVZ hyperplasia. However, early mortality due to hydrocephalus prevented further tumourigenesis in vivo and therefore must be overcome in future modeling endeavours. Despite this, we pioneered the application of the SB mutagenesis system for establishing a functional genomics mouse model of ependymoma with which specific genetic events driving ependymoma tumourigenesis may be uncovered by analyzing resultant tumours for SB insertions. Next, we attempted to develop an allograft mouse model of CIMP-positive PFA ependymoma by over-activating EZH2 in embryonic hindbrain RGCs followed by intracranial implantation into NSG mice. EZH2 over-activation did not lead to higher tumour incidence but its inhibition caused significant reduction in tumour cell self-renewal. The tumours appeared highly malignant and undifferentiated but did not fit with the diagnosis of ependymoma or any other known human brain tumour. Future modeling therefore requires better understanding of the tumourigenic mechanism along with more precise identification and isolation of its cells of origin in order to more accurately recapitulate this disease.Ph.D