ORIGINAL ARTICLE

Abstract Studies on smooth muscle cell differentiation and those on vascular development in mouse and humans have long been hampered by the lack of suitable markers. Here we describe a novel, large isoform of smoothelin, a structural protein of differentiated, contractile smooth muscle cells. The protein, which is highly conserved in mouse and humans, shows homology with other cytoskele-ton-associated smooth muscle cell proteins and contains an actinin-type actin-binding domain. Northern blot analy-sis from various mouse organs identified short and long smoothelin mRNA forms, which exhibit distinct tissue ex-pression patterns. The short form is highly expressed in visceral muscle tissues such as intestine and stomach and is not detectable in brain, while the long mRNA form is expressed in all vascularized organs. These results may provide new tools and approaches to study both smooth muscle cell differentiation and proliferative vascular dis-ease. Key words Smooth muscle cell differentiation · Proliferative vascular disease · Actinin-type actin-binding domain · Smooth muscle cell marker · Cytoskeleton-associated protein Abbreviations PCR Polymerase chain reaction · RACE Rapid amplification of cDNA ends · SDS Sodium dodecyl sulfate · VSMC Vascular smooth muscle cel