Massachusetts General Hospital Cancer Center, Charlestown, Massachusetts 02129, USA.
To explore the physiological role of p107, a member of retinoblastoma gene (Rb) family, we disrupted the mouse gene by homologous recombination in embryonic stem cells. p107 homozygous mutant mice were viable, fertile, and displayed no obvious abnormalities. To investigate possible functional overlap between p107 and Rb, mice with mutations at both loci were generated. Rb+/-;p107-/- mice have a pronounced growth retardation and increased mortality rate during the first 3 weeks after birth. The Rb+/-;p107-/- pups that survive to adulthood did not show any altered tumor predisposition when compared with Rb+/- mice but developed multiple dysplastic lesions of the retina. Embryos homozygous for both Rb and p107 died at approximately 11.5 days of gestation, 2 days earlier than embryos homozygous for Rb alone. Histological examination revealed accelerated apoptosis in the liver and the central nervous system of Rb-/-;p107-/- embryos relative to Rb-/- embryos. These results provide the first in vivo evidence that p107 and Rb have overlapping functions in some tissues of the developing and adult mouse.