Differential expression of two skeletal muscle beta-tropomyosin mRNAs during Xenopus laevis development

A cDNA clone for a Xenopus laevis skeletal muscle beta-tropomyosin (beta-TM ad) isoform was isolated from an adult skeletal muscle cDNA library. Sequen ce analysis revealed that this clone corresponded to a second beta-tropomyo sin mRNA distinct from the one that was previously characterized (beta-TMem b). The two skeletal beta-TM mRNAs originate from distinct genes and are di fferentially expressed during development. beta-TMemb mRNA is expressed onl y in the somites of the early embryo while beta-TMad mRNA is expressed in p re-metamorphic tadpoles and adult skeletal muscles. We have isolated the pr omoter region of the beta-TMemb gene and shown that a DNA construct contain ing 2.9 kb of promoter region is properly expressed after injection in the embryo.