Astrocyte inactivation of the pRb pathway predisposes mice to malignant astrocytoma development that is accelerated by PTEN mutation. 
We have inactivated pRb, p107, and p130 in astrocytes by transgenic expression of T(121) (a truncated SV40 T antigen) under the GFAP promoter.  Founder mice died perinatally with extensive expansion of neural precursor and anaplastic astrocyte populations.  In astrocytes, aberrant proliferation and extensive apoptosis were induced.  Using a conditional allele of T(121), early lethality was circumvented, and adult mice developed high-grade astrocytoma, in which regions of decreased apoptosis expressed activated Akt.  Indeed, astrocytoma development was accelerated in a PTEN(+/-), but not p53(+/-), background.  These studies establish a highly penetrant preclinical model for astrocytoma based on events observed in the human disease and further provide insight into the role of PTEN mutation in astrocytoma progression.