Tissues were fixed in formalin, paraffin embedded, and sectioned at 5 microns, and were stained with hematoxylin and eosin (H&E), or prepared for immunostaining as previously described.[10 (link), 26 , 27 (link)] Images were captured on a Nikon Eclipse NI-U with a DS-QI1 or DS-Ri1 camera and NIS Elements software, and adjusted in Adobe Photoshop. Antibodies were as follows: rabbit anti-Krt10, chicken anti-Krt5, mouse anti-Krt8, and rabbit anti-Ki-67. Alexafluor 488, 546, and 647 secondary antibodies were from Thermo Fisher Scientific. Whole-mount in situ hybridization was performed on embryos with digoxigenin-labeled riboprobes, as described.[28 (link)] β-galactosidase staining was carried out as described[29 ]. Whole mount images were captured on a Leica MZ16 stereomicroscope and QImaging 5.0 RTV digital camera.