RB1 and glioma: A gene recombination directly within the stem/progenitor cell compartment of the SVZ [140] demonstrated also that the brain tumour phenotype was strongly influenced by the gene recombination, with gliomas arising from recombination of Pten and p53, and primitive, poorly differentiated embryonal tumours from a recombination of Rb and p53, or by recombining Rb, Pten and p53; however, these experiments also demonstrated the essential role of p53 in CNS tumourigenesis, whereas the recombination of Rb and Pten alone did not generate CNS tumours [140].