Figure 7. Conditional Rb^−/−;E2f4^−/− embryos exhibit Rb and E2f4 mutant phenotypes at E18.5.

A) Control, E2f4^−/−, Rb^1lox/1lox;Meox^cre/+ (cRb^−/−) and Rb^1lox/1lox;E2f4^−/−;Meox^cre/+ (cRb^−/−; E2f4^−/−, DKO) embryos at E18.5. DKO embryos are growth retarded, like E2f4^−/− mice, and have a hunched appearance similar to cRb^−/− embryos. B) Skeletal staining with Alcian blue (cartilage) and Alizarin red (bone) of control and mutant embryos reveals altered curvatures of the spine and ribcage in the cRb^−/− and DKO embryos. C) Decrease in muscle density and fiber organization in the Rb mutants is unchanged with the additional loss of E2F4 as judged by hematoxylin and eosin staining. Magnification, 40x. D) Darkly stained BrdU-positive cells were detected in the lens fiber cell compartment (indicated by the black arrows) in the cRb^−/− and DKO lenses, but not in the control and E2f4^−/− lenses. Magnification, 40x. E) Giemsa stained peripheral blood smears from control and mutant animals. There are a considerable percentage of erythroblasts containing Howell-Jolly bodies (white arrowheads) following the loss of E2F4 while the loss of pRB leads to a number of immature nucleated erythroblasts (black arrowheads). Both of these phenotypes are present in DKO blood preparations.