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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2000;20:907.)
© 2000 American Heart Association, Inc.

Vascular Biology

Fibroblast Growth Factor Plays a Critical Role in SM22 Expression During Xenopus Embryogenesis

Toru Oka; Ichiro Shiojima; Koshiro Monzen; Sumiyo Kudoh; Yukio Hiroi; Koichiro Shiokawa; Makoto Asashima; Ryozo Nagai; Yoshio Yazaki; Issei Komuro

From the Department of Cardiovascular Medicine, Graduate School of Medicine (T.O., I.S., K.M., S.K., Y.H., R.N., Y.Y., I.K.), the Laboratory of Molecular Embryology, Department of Biological Sciences, Graduate School of Science (K.S.), and the Department of Life Sciences (Biology), Graduate School of Arts and Sciences (M.A.), University of Tokyo, Tokyo, Japan.

Correspondence to Dr Issei Komuro, Department of Cardiovascular Medicine, University of Tokyo Graduate School of Medicine, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan. E-mail komuro-tky{at}umin.ac.jp

Abstract—Although smooth muscle cells (SMCs) are critical components of the circulatory system, the regulatory mechanisms of SMC differentiation remain largely unknown. In the present study, we examined the mechanism of SMC differentiation by using Xenopus laevis SM22 (XSM22) as an SMC-specific marker. XSM22 cDNA contained a 600-bp open reading frame, and the predicted amino acid sequences were highly conserved in evolution. XSM22 transcripts were first detected in heart anlage, head mesenchyme, and the dorsal side of the lateral plate mesoderm at the tail-bud stage, possibly representing the precursors of muscle lineage. At the tadpole stage, XSM22 transcripts were restricted to the vascular and visceral SMCs. XSM22 was strongly induced by basic fibroblast growth factor (FGF) in animal caps. Although expressions of Xenopus cardiac actin were not affected by the expression of a dominant-negative FGF receptor, its injection dramatically suppressed the XSM22 expression. These results suggest that XSM22 is a useful molecular marker for the SMC lineage in Xenopus and that FGF signaling plays an important role in the induction of XSM22 and in the differentiation of SMCs.

Key Words: smooth muscle cells • SM22 • basic fibroblast growth factor • dominant-negative fibroblast growth factor receptor