Characterization of nucleologenesis and ribosomal synthesis in Emg1-/- embryos. (A) Immunofluorescence staining for the nucleolar markers B23/nucleophosmin and fibrillarin. In E3.5 Emg1+/+ embryos, the nucleoli are smaller and more irregular than the NPBs in E2.5 morulae. The nucleoli in E3.5 Emg1-/- mutants, however, display a large sphere shape, which closely resemble NPBs as seen in E2.5 wild-type embryos. (B) RT-PCR on E2.5 morulae harvested from Emg1+/- intercrosses. Arrows indicate the morulae that lack Emg1 mRNA but show a similar level of 18S rRNA to that of Emg1-expressing morulae. The genotypes for each sample are also presented. M: 50 bp or 100 bp DNA markers. (C) RT-PCR on E3.5 Emg-/- embryos, showing similar levels of 18S rRNA and pre-rRNA in both mutant and wild-type embryos.