Tropomyosin gene expression in vivo and in vitro.

The evolution from unicellular to multicellular organisms of increasing complexity is paralleled by increased numbers of tropomyosin (Tm) genes and increasing numbers ofisoforms encoded by each gene. The regulation of Tm isoform expression is intimately associated with the morphological changes that take place during development and cell differentiation. The tissue- and cell-specific Tm expression patterns are regulated at multiple levels, allowing precise spatial and temporal regulation of Tm expression. In this chapter, we review the Tm isoform expression pattern during differentiation of different tissue types and from this data infer some general principles regarding Tm expression patterns during differentiation. Finally, we review the mechanisms that account for the highly regulated repertoire ofTm isoform expression.