Distribution of phosphorylated Smad2 identifies target tissues of TGFβ ligands in mouse development

Transforming growth factor β (TGFβ) and related family members control the development of tissues by regulating cell proliferation, differentiation, migration and apoptosis. They transmit signals to the nucleus via phosphorylation of Smad proteins. Here, we used an antibody specifically recognising phosphorylated Smad2 (PSmad2) to identify tissues that have received signals of TGFβ family members acting via Smad2, e.g. TGFβs, activins and nodal. At embryonic day (E)5.5–E8.5, punctuated nuclear PSmad2 staining was scattered throughout the embryo. At E10.5–E12.5, specific zones of the neural tube and brain, ganglia, premuscle masses and precartilage primordia exhibited pronounced nuclear staining, while tissues undergoing epithelial–mesenchymal interactions showed prominent cytoplasmic staining. Interestingly, in the endocardium and most endothelial cells PSmad2 is not detected at E10.5–E12.5, although at E8.5 these cells were stained. These data document the cells that may have received a TGFβ-like stimulus and illustrate, for the first time, the dynamic regulation in space and time of phosphorylated Smad2 during mouse development.