Fig 5. Foxa2 lineage-positive cells maintain Foxa2 expression at the mid-late steak stage.

(A, B) Representative embryos at the early (A) and mid-late (B) streak stages resulting from the administration of tamoxifen at E6+8h in Foxa2^{nGPF-CreERT2/+}; R26R^tdTomato/+ immunostained for Foxa2 (green) and T (blue). View is lateral in (A) and posterior in (B). (B”) Schematics of the embryo shown in (B). (C) Same embryo as in (B). Single optic sections are shown. (i–iii) are magnified views of the insets. Yellow arrows point to double Foxa2/T positive, blue arrows to Foxa2 positive T negative, and red arrows to Foxa2 negative T positive tdTomato-expressing cells. (D) Representative example of a segmented image based on Foxa2 and T signal. (E) Quantification of T and Foxa2 signal intensities along the proximal-distal axis of the embryo in single cell nuclei. All the tdTomato-positive cells are all located in the distal (anterior) portion of the primitive streak. The data underlying (E) can be found in S4 Source Data. (F) Quantification of Foxa2 and T intensities in single cell in distal (green), proximal (blue) primitive streak cells and tdTomato-positive cells. The data underlying (F) can be found in S4 Source Data. (G, H) Model. As the primitive streak extend along the proximal-distal axis, from the early to mid-late streak stages, a subset of the Foxa2-positive cells switch contribution from endoderm to cardiac (ventricles) progenitors and express T. ES, early streak; LV, left ventricle; MS, mid-streak; PS, primitive streak.