A Novel Alternative Exon of the Caenorhabditis Elegans Lev-11 Tropomyosin Gene is used to Express a Head-Muscle-Specific Isoform

Tropomyosin (TM) is a coiled-coil dimer that binds along actin filaments in both muscle and non-muscle cells. TM is involved in cellular processes including muscle contraction, cell motility, and cell division. In mammals, more than 40 isoforms of TM are expressed from four genes through extensive alternative splicing. Isoform-specific actin cytoskeletal regulation is also achieved by tissue-specific expression and subcellular localization. We utilized the nematode Caenorhabditis elegans to study functional diversity of TM isoforms. In C. elegans, previous studies reported four TM isoforms from a single gene, lev-11, by alternative promotors and splicing. Two high-molecular-weight (HMW) isoforms are expressed by use of the upstream promoter and encoded by nine exons; whereas two low-molecular-weight isoforms are expressed from the downstream promoter and encoded by seven exons. In these four isoforms, exons 6, 7, and 8 were constitutive. Through analysis of Expressed Sequence Tag sequences and RT-PCR, we ...