SMOOTH-MUSCLE ALTERNATIVE SPLICING INDUCED IN FIBROBLASTS BY HETEROLOGOUS EXPRESSION OF A REGULATORY GENE

Alternative splicing is a common mechanism for regulating gene express ion in different cell types. In order to understand this important pro cess, the transacting factors that enforce the choice of particular sp licing pathways in different environments must be identified. We have used the rat alpha-tropomyosin gene as a model system of tissue-specif ic alternative splicing. Exon 3 of alpha-tropomyosin is specifically i nhibited in smooth muscle cells allowing the alternative inclusion of exon 2. We have used a novel gene transfer and selection strategy to d etect a gene whose expression in fibroblasts is sufficient to switch t hem to smooth muscle-specific splicing of alpha-tropomyosin and also a lpha-actinin. Extracts from the regulating fibroblasts contain an appa rently novel 55 kDa protein which binds to RNA elements required for r egulation of tropomyosin splicing. This protein is not detected in ext racts of non-regulating cells and is therefore a strong candidate-cell -specific splicing regulator. These experiments advance our understand ing of smooth muscle splicing regulation as well as establishing a mea ns for direct cloning of tissue-specific splicing regulators which hav e so far been refractory to biochemical analysis.