Tissue-specific expression of rat myosin light-chain 2 gene in transgenic mice.

One approach to determining how the differential expression of specific genes is regulated in higher organisms is to introduce cloned copies of the genes (or parts of the genes) into the genomes of individual organisms from the very beginning of their development. The way in which the exogenous genetic information behaves during the development of the experimental organisms can then provide a means of defining the DNA sequences that restrict the expression of the gene to specific cell types and times of development. So far, several different genes have been introduced into the genomes of mice, but in only a few cases have the exogenous genes retained the tissue specificity of expression of the equivalent endogenous genes. I report here that in two out of three 'transgenic' mice carrying copies of the rat gene for skeletal muscle myosin light chain 2, the exogenous gene is expressed specifically in skeletal muscle cells. The sequences contained in the cloned copy of the myosin light-chain 2 gene used in these experiments are thus sufficient to confer a tissue-specific pattern of expression.