Ependymomas are the third most common brain cancer in children. Attempts to determine optimum therapies of ependymoma have been hindered by the low incidence of disease, a poor understanding of the disease’s biological characteristics and lack of in vivo and in vitro models. We aim to study the role of recurrent ependymoma genetic events using spatial and temporal regulation of cre in radial glia, the cell of origin for ependymoma. Radial glia are specialised cells within the developing central nervous system (CNS) that serve as primary progenitors capable of generating neurons, astrocytes, and oligodendrocytes. The availability of appropriate molecular tools to manipulate gene expression in vivo is therefore critical to further our understanding of the contributions made by radial glia to normal brain development and disease states such as ependymoma.
To this end, we have characterised cre recombinase activity in a novel transgenic mouse in which the coding sequence of a cre/progeseterone receptor fusion protein (CrePR) is knocked into the gene encoding the radial glia specific marker Fabp7/Blbp. Nuclear localisation, and thus temporal control, of cre is activated by injection of mice with a synthetic progesterone analog, RU486. To characterise this inducible system, Rosa26-LSL-LacZ reporter mice were bred with Fabp7-crePR knock-in mice to generate offspring where transcription of β-galactosidase does not occur until activation of CrePR using RU486. Cre activity was induced at postnatal day 0 (P0) and 7 (P7). Brain tissue from mice was subsequently assessed for β-galactosidase activity using histochemisty and immunofluorescence as a marker of cre-mediated recombination. β-galactosidase staining was observed in cells of the radial glia lineage including cortical astrocytes, Bergmann glia and neural progenitor cells. The RU486-mediated activation of CrePR in these mice was found to affect more cells at P0 compared to induction at P7, which is consistent with the known patterns of expression of the endogenous Fabp7 gene. β-galactosidase histochemistry assays were found to underestimate the extent of cre-mediated recombination when compared to immunofluorescence staining. Further characterisation of cre activity is currently being undertaken using multiple other reporter mouse strains including Rosa26-LSL-TdTomato mice, and lineage tracing of radial glia is being assessed using the Brainbow2.1 mice.