E2F4 cooperates with pRB in the development of extra-embryonic, not embryonic, tissues

Homozygous mutation of the murine retinoblastoma tumor suppressor gene, Rb, results in embryonic lethality between E13.5 and E15.5 with defects in cellular proliferation, differentiation and apoptosis. Many of these defects are suppressed by mutation of an activating E2F, E2f1 or E2f3, indicating that they are key downstream targets of the retinoblastoma protein, pRB. In this study, we assess how E2F4 contributes to the developmental consequences of pRb-loss. In stark contrast to the activating E2Fs, the homozygous mutation of E2f4 shortened the lifespan of Rb-/- embryos. This resulted from an exacerbation of the placental defect of the Rb-/- mice indicating that E2F4 and pRB cooperate in the development of this tissue. Further analyses indicated that this defect reflects an increase in trophectoderm-like cells. Under conditions where the placenta was wild-type but the embryo mutant for E2f4 and pRb embryos survived to birth and exhibited all of the defects that were observed in the E2f4 and Rb single mutant embryos. Thus, while pRB and E2F4 cooperate in placental development, they play largely non-overlapping roles the development of many embryonic tissues.

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