Oded Singer

Glioblastoma multiforme (GBM) is the most common and aggressive malignant primary brain tumor in humans. Here we show that gliomas can originate from differentiated cells in the central nervous system (CNS), including cortical neurons. Transduction by oncogenic lentiviral vectors of neural stem cells (NSCs), astrocytes, or even mature neurons in the brains of mice can give rise to malignant gliomas. All the tumors, irrespective of the site of lentiviral vector injection (the initiating population), shared common features of high expression of stem or progenitor markers and low expression of differentiation markers. Microarray analysis revealed that tumors of astrocytic and neuronal origin match the mesenchymal GBM subtype. We propose that most differentiated cells in the CNS upon defined genetic alterations undergo dedifferentiation to generate a NSC or progenitor state to initiate and maintain the tumor progression, as well as to give rise to the heterogeneous populations observed in malignant gliomas.

We describe the use of lentiviral vectors expressing small interfering RNAs (siRNAs) to knock down the expression of specific genes in vitro and in vivo. A lentiviral vector capable of generating siRNA specific for GFP after transduction of 293T-GFP cell lines showed no GFP fluorescence. Furthermore, no GFP-specific RNA could be detected. When eggs from GFP-positive transgenic mice were transduced with lentivirus-expressing siGFP virus, reduced fluorescence could be seen in blastocysts. More interestingly, pups from F(1) progeny, which expressed siGFP, showed considerably diminished fluorescence and decreased GFP. We propose that an approach of combining transgenesis by lentiviral vectors expressing siRNAs can be used successfully to generate a large number of mice in which the expression of a specific gene(s) can be down-regulated substantially. We believe that this approach of generating "knockdown" mice will aid in functional genomics.