Early “first wave” alpha cells are present in mouse models despite the deletion of factors necessary for pancreas development and endocrine specification. Sagittal sections of E10.5 embryos from a representative wildtype littermate (A), Pdx1 null (B), Ptf1a null (C), Neurog3 null (D), Nkx2-2 null (E), and pancreas-specific deletion of Arx (F), were stained by immunofluorescence for the hormone glucagon (A–F). In all images glucagon-expressing cells are present. All images are of the dorsal pancreas. DAPI marks all nuclei. 40X