Figure 1. Rho GTPase functions in epithelial development. (A) Rhou is expressed in the foregut (fg) endoderm (en) of mouse embryos at embryonic day 9.5. Expression is downregulated in the ventral midline where the thyroid bud (t) emerges. (B) The foregut endoderm consists of polarized columnar epithelial cells with F-actin (red, visualized with phalloidin) concentrated beneath the apical surface, and a basement membrane containing fibronectin (green, visualized by immunofluorescence). (C) The foregut endoderm forms tight junctions apically (red, visualized by ZO-1 immunofluorescence) and adherens junctions (green, visualized by E-cadheren immunofluorescence) laterally. (D) Rho GTPases have multiple functions in epithelia. Rho GTPases interact with effector proteins to influence cell polarity, actin localization and cell junction formation. In turn, this affects tissue organization and lineage differentiation. (E and F) Electroporation of a construct encoding GFP-tagged Rhou (green) into the foregut endoderm reveals that its subcellular distribution overlaps with that of F-actin (red). (D) Merged image of GFP and phalloidin staining. (E) Phalloidin staining only. (B and C; E and F) Apical aspect is at the top of the figure, basal is at the bottom.