Pitx2 is required for smooth muscle cell differentiation in branchial arch arteries and dorsal aorta

Mechanisms controlling differentiation of smooth muscle cells (SMCs) are poorly understood. We recently identified the Pitx2 gene as a homeodomain transcription factor which was rapidly induced in an in vitro inducible SMC differentiation system. The aim of the present study was to determine the role of Pitx2 in SMC differentiation. Results showed that overexpression of Pitx2 induced expression of multiple SMC differentiation marker genes including SM α‐actin, SM22α, and h1‐calponin in A404 SMC progenitor cells, whereas siRNA‐induced knockdown of Pitx2 attenuated retinoic acid‐induced SMC differentiation of A404 cells. Moreover, homozygous knockout of the Pitx2 gene impaired differentiation of embryonic stem cells into SMC in an embryoid body model in vitro. Of major significance, analysis of Pitx2 knockout mouse embryos revealed that expression of SMC differentiation marker genes including SM α‐actin and SM22α were nearly abolished in both the branchial arch arteries and the dorsal aorta at E11.5. In contrast, expression of endothelial cell marker, PECAM‐1 was unaltered, suggesting the cell‐selective role of Pitx2 in SMCs, but not in endothelial cells.. Taken together, these results provide evidence that Pitx2 is required for expression of SMC differentiation marker genes during embryonic development.