Expression of the Smooth Muscle Cell Calponin Gene Marks the Early Cardiac and Smooth Muscle Cell Lineages during Mouse Embryogenesis

Joseph M Miano,Eric N Olson

doi:10.1074/jbc.271.12.7095

Abstract

Although several genes are considered markers for vascular smooth muscle cell (SMC) differentiation, few have been rigorously tested for SMC specificity in mammals, particularly during development where considerable overlap exists between different muscle gene programs. Here we describe the temporospatial expression pattern of the SMC calponin gene (formerly h1 or basic calponin) during mouse embryogenesis and in adult mouse tissues and cell lines. Whereas SMC calponin mRNA expression is restricted exclusively to SMCs in adult tissues, during early embryogenesis, SMC calponin transcripts are expressed throughout the developing cardiac tube as well as in differentiating SMCs. Transcription of the SMC calponin gene initiates at two closely juxtaposed sites in the absence of a consensus TATAA or initiator element. Transient transfection assays in cultured SMC demonstrated that high level SMC calponin promoter activity required no more than 549 nucleotides of 5 sequence. In contrast to the strict cell type-specificity of SMC calponin mRNA expression, the SMC calponin promoter showed activity in several cell lines that do not express the endogenous SMC calponin gene. These results demonstrate that SMC calponin responds to cardiac and smooth muscle gene regulatory programs and suggest that the cardiac and smooth muscle cell lineages may share a common gene regulatory program early in embryogenesis, which diverges as the heart matures. The finding that the isolated SMC calponin promoter is active in a wider range of cells than the endogenous SMC calponin gene also suggests that long-range repression or higher order regulatory mechanism(s) are involved in cell-specific regulation of SMC calponin expression.

Highlights

The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) U37071 and U28932
The discovery of cell-specific transcription factors that trigger differentiation in skeletal and cardiac muscle has led to a search for similar regulatory factors in smooth muscle cells (SMCs),1 whose differentiation program is impaired during the course of intimal disease [1]
SMC calponin was expressed in proliferating BC3H1 cells, which have been reported to exhibit properties of smooth and skeletal muscle, and only weakly in the differentiated P19 embryonal carcinoma cell line, which has the potential to differentiate into smooth muscle [38] (Fig. 1B)

Summary

Introduction

The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) U37071 and U28932. Given the similarities between skeletal, cardiac, and smooth muscle cells, it is reasonable to anticipate that these different muscle cell types may share certain aspects of a myogenic gene regulatory program. SM22␣ is expressed in cardiac, skeletal, and smooth muscle cells in the embryo before becoming restricted to SMCs late in embryogenesis [14, 15]. Dissection of the cis-acting regulatory elements associated with these and other SMC genes will be an important step toward understanding the similarities and differences in the myogenic regulatory programs in the three major muscle cell types. Defining SMC-specific transcription factors that activate the SM ␣-actin promoter, is complicated by its expression in multiple cell types during embryogenesis and in the adult [11,12,13]. No cis elements have been shown to confer SMC-specific expression of these promoters

Methods

Results

Conclusion