FIGURE 2.

TopBP1 disruption results in early embryonic lethality. A, images of embryos at E3. 5 were obtained under bright-field conditions. The embryos were classified according to their appearance: morula, early stage of blastocyst, and mature blastocyst. B, outgrowth of wild-type, heterozygote, and mutant blastocysts (see “Experimental Procedures”) is shown. Blastocyst stage embryos recovered at E3.5 were cultured in vitro for several days and subsequently genotyped by PCR. Embryo outgrowths are composed of an inner cell mass surrounded by a single layer of trophoblast giant cells. C, hematoxylin and eosin staining of histologic sections were performed to analyze the appearance of E7.5 embryos developing in the uterus. Typical images of wild-type and fully resorbed mutant embryos are displayed in the left and right panels, respectively.