Dp1 Is Largely Dispensable for Embryonic Development

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Abstract
E2F/DP complexes activate or repress the transcription of E2F target genes, depending on the association of a pRB family member, thereby regulating cell cycle progression. Whereas the E2F family consists of seven members, the DP family contains only two (Dp1 and Dp2), Dp1 being the more highly expressed member. In contrast to the inactivation of individual E2F family members, we have recently demonstrated that loss of Dp1 results in embryonic lethality by embryonic day 12.5 (E12.5) due to the failure of extraembryonic lineages to develop and replicate DNA properly. To bypass this placental requirement and search for roles of Dp1 in the embryo proper, we generated Dp1-deficient embryonic stem (ES) cells that carry the ROSA26-LacZ marker and injected them into wild-type blastocysts to construct Dp1-deficient chimeras. Surprisingly, we recovered mid- to late gestational embryos (E12.5 to E17.5), in which the Dp1-deficient ES cells contributed strongly to most chimeric tissues as judged by X-Gal (5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside) staining and Western blotting. Importantly, the abundance of DP2 protein does not increase and the expression of an array of cell cycle genes is virtually unchanged in Dp1-deficient ES cells or chimeric E15.5 tissues with the absence of Dp1. Thus, Dp1 is largely dispensable for embryonic development, despite the absolute extraembryonic requirement for Dp1, which is highly reminiscent of the restricted roles for Rb and cyclins E1/E2 in vivo.