Two skeletal alpha-tropomyosin transcripts with distinct 3 ' UTR have different temporal and spatial patterns of expression in the striated muscle lineages of Xenopus laevis

The Xenopus laevis alpha-tropomyosin (TM) gene, like its vertebrates counte rparts, encodes muscle and non-muscle isoforms through two promoters and al ternatively spliced exons. In the present study we describe a cDNA clone (X TM alpha 7) encoding a skeletal muscle isoform of the gene that differs fro m the previously described skeletal TM transcript (XTM alpha 2) by its 3'UT R sequence. The two skeletal alpha-TM encoding mRNAs are generated through distinct 3'end processing using different polyA signals and distinct patter ns of exon splicing. Using RNAse protection and RNA in situ hybridization, we have analysed the developmental and spatial expression of the two transc ripts. Both are expressed in the embryo, but XTM alpha 7 is by far the most prevalent of the two. In contrast, only XTM alpha 2 is expressed in adult striated muscle tissues. In the embryo, the spatial expression of XTM alpha 7 is restricted to the somites whereas XTM alpha 2 is expressed in both so mites and embryonic heart. (C) 1999 Elsevier Science Ireland Ltd. All right s reserved.