title: Modular proteins from the Drosophila sallimus (sls) gene and their expression in muscles with different extensibility.
abstract: The passive elasticity of the sarcomere in striated muscle is determined by large modular proteins, such as titin in vertebrates. In insects, the function of titin is divided between two shorter proteins, projectin and sallimus (Sls), which are the products of different genes. The Drosophila sallimus (sls) gene codes for a protein of 2 MDa. The N-terminal half of the protein is largely made up of immunoglobulin (Ig) domains and unique sequence; the C-terminal half has two stretches of sequence similar to the elastic PEVK region of titin, and at the end of the molecule there is a region of tandem Ig and fibronectin domains. We have investigated splicing pathways of the sls gene and identified isoforms expressed in different muscle types, and at different stages of Drosophila development. The 5' half of sls codes for zormin and kettin; both proteins contain Ig domains and can be expressed as separate isoforms, or as larger proteins linked to sequence downstream. There are multiple splicing pathways between the kettin region of sls and sequence coding for the two PEVK regions. All the resulting protein isoforms have sequence derived from the 3' end of the sls gene. Splicing of exons varies at different stages of development. Kettin RNA is predominant in the embryo, and longer transcripts are expressed in larva, pupa and adult. Sls isoforms in the indirect flight muscle (IFM) are zormin, kettin and Sls(700), in which sequence derived from the end of the gene is spliced to kettin RNA. Zormin is in both M-line and Z-disc. Kettin and Sls(700) extend from the Z-disc to the ends of the thick filaments, though, Sls(700) is only in the myofibril core. These shorter isoforms would contribute to the high stiffness of IFM. Other muscles in the thorax and legs have longer Sls isoforms with varying amounts of PEVK sequence; all span the I-band to the ends of the thick filaments. In muscles with longer I-bands, the proportion of PEVK sequence would determine the extensibility of the sarcomere. Alternative Sls isoforms could regulate the stiffness of the many fibre types in Drosophila muscles.
authors.affiliation: Institut für Anästhesiologie und Operative Intensivmedizin, Universitätsklinikum Mannheim, D-68167 Mannheim, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Burkart
authors.forename: Feng
authors.initials: F
authors.lastname: Qiu
authors.forename: Sigrun
authors.initials: S
authors.lastname: Brendel
authors.forename: Vladimir
authors.initials: V
authors.lastname: Benes
authors.forename: Petra
authors.initials: P
authors.lastname: Hååg
authors.forename: Siegfried
authors.initials: S
authors.lastname: Labeit
authors.forename: Kevin
authors.initials: K
authors.lastname: Leonard
authors.forename: Belinda
authors.initials: B
authors.lastname: Bullard
mesh_terms: D024506:5' Flanking Region; D008841:Actin Cytoskeleton / Q000378:metabolism; D000818:Animals; D030801:Animals, Genetically Modified; D064211:Connectin; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics* / Q000254:growth & development; D004548:Elasticity; D004625:Embryo, Nonmammalian; D015870:Gene Expression; D008954:Models, Biological; D024510:Muscle Development / Q000235:genetics; D009124:Muscle Proteins / Q000235:genetics* / Q000378:metabolism*; D009132:Muscles / Q000196:embryology / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D013909:Thorax / Q000378:metabolism
chemical_list: D064211:Connectin; D029721:Drosophila Proteins; D009124:Muscle Proteins; D020033:Protein Isoforms; C577347:sls protein, Drosophila