<i>Dullard<sup>−/−</sup></i> embryos fail to form primordial germ cells (PGCs).

<p>(<b>A–H</b>) Absence of alkaline phosphatase (AP)-positive PGCs in <i>Dullard<sup>−/−</sup></i> embryos at the (<b>A, B</b>) E7.75 neural plate stage (<b>A′</b>, <b>B′</b>; higher magnification views) and (<b>C–D</b>) E8.5 early somite stage (<b>C′</b>, <b>D′</b>; higher magnification views). (<b>E–H</b>) Histology of E7.5 (<b>E, E′</b>) <i>Dullard<sup> +/−</sup></i> and (<b>F, F′</b>) <i>Dullard<sup>−/−</sup></i> embryos revealing the absence of AP-positive cells in the endoderm of <i>Dullard<sup>−/−</sup></i> embryos, while few positive cells in the mesoderm displayed (<b>H</b>) the characteristic staining pattern (in the cell membrane and a cytoplasmic aggregate) of PGCs in the endoderm of (<b>G</b>) <i>Dullard<sup> +/−</sup></i> embryos. (<b>I, J</b>) Markedly reduced population of Dppa3-expressing cells in the E7.5 <i>Dullard<sup>−/−</sup></i> embryo (confocal images). (<b>K, L′′</b>) No clustering of Ifitm3-positive cells in the E7.5 <i>Dullard<sup>−/−</sup></i> embryo. (<b>K, L</b>; whole embryo bright-field view; <b>K′, L′</b>; immunostaining, <b>K′′</b>, <b>L′′</b>; high magnification views of Iftim3-positive (red) cells in the boxed areas of <b>K′</b> and <b>L′</b>; DAPI nuclear staining (blue). (<b>M–N</b>) Marked reduction in the numbers of <i>Prdm1</i>-positive cells in the E7.25 streak-stage <i>Dullard<sup>−/−</sup></i> embryo (<b>M′</b>, <b>N′</b>; high magnification views of the boxed areas in <b>M, N</b>, respectively). (<b>O–P′′</b>) Down-regulation of <i>Ifitm1</i> expression in the posterior mesoderm of the E7.5 <i>Dullard</i><sup>−/−</sup> embryo [<b>O, P</b>, whole embryo; <b>O′, P′</b>, merged bright-field and immunofluorescence images (boxed area); <b>O′′, P′′</b>, immunofluorescence image only]. (<b>A, A′, C, C′, E, E′, G, I, K–K′′, M, M′, O–O′′</b>) <i>Dullard<sup> +/−</sup></i> embryos; (<b>B, B′, D, D′, F, F′, H, J, L–L′′, N, N′, P–P′′</b>) <i>Dullard<sup>−/−</sup></i> embryos. (<b>E, F</b>) Dashed lines indicate the plane of sectioning. (<b>E′, F′</b>) Dashed lines mark the basal surface of the endoderm layer. Scale bars = 100 µm (<b>A–F′, K–L′, M–P′</b>′), 50 µm (<b>I, J</b>) and 25 µm (<b>K′′, L′</b>′).</p>