Isl1 is expressed in developing mouse stomach. (A) Embryonic stomach WISH analysis demonstrated that Isl1 expression was limited to the pylorus at E13.5 (arrow). (B) Immunohistochemical staining for Isl1 in stomach. Sections from embryos were arranged in rostral to caudal sequence at E11.5 and E13.5, and Isl1 expression was mainly localized to the mesenchyme of the posterior stomach. At E14.5 and E18.5, Isl1 was highly expressed in smooth muscle cells of the pylorus, although there were some Isl1-positive cells in the lamina propria (arrowheads). Enlarged images in boxed regions are shown below original images. D, duodenum; Liv, liver; Pa, pancreas; St, stomach. Scale bars of original images: 100 μm; scale bars of enlarged images: 50 μm.