Fog2 is expressed in the diffuse pulmonary mesenchyme at E13.5 (A) (arrow shows mesenchyme) and is restricted to the bronchial and vascular smooth muscle (sm) at E16.5 (B). Fog2 is expressed diffusely in the developing diaphragm (Dia) both prior to (E11.5) (C) and after muscularization (E13.5) (D).