Gap junction coupling across endoderm of wild-type but not <i>Sox17</i> mutant embryos.

<p>(A and B) Experimental scheme. (C–D) Brightfield image and MIP of posterior view of ∼6 somite stage wild-type embryo, emVE cell on left side injected. (E) High magnification, injected cell retaining Alexa-568 (red). (F) Neurobiotin (white) visualized over several cell diameters. (G) Merge showing propagation of Neurobiotin through emVE-derived (GFP-positive) and the DE-derived (GFP-negative) gut endoderm cells. (H and I) 2-D/orthogonal views at dashed line in (C) showing Neurobiotin signal localized to endoderm epithelium and absent mesoderm. (J–L) Bilateral injection within gut endoderm of 0–1 somite stage wild-type embryo revealing exclusion of Neurobiotin from node/midline. (M and N) Brighfield and fluorescent merge of posterior views of a ∼5 somite stage <i>Sox17</i>^{−<i>/</i>−}<i>; Afp::GFP^Tg/+</i> injected into a left-sided gut endoderm cell. (O–Q) High magnifications show retention of Alexa-568 and Neurobiotin. (R–V) Bilateral injection of endoderm cells in 0–1 somite stage mutant depicting retention of Neurobiotin. GFP-negative line near the node (asterisk) is an artifact resulting from grid used for embryo positioning. m, midline; n, node; ys, yolk sac; mes, mesoderm; end, endoderm; A, anterior; L, left; P, posterior; R, right. Scale bars = 100 µm in (D, N, and S); 50 µm in (G and L); 20 µm in (Q and V).