title: Mutation that dramatically alters rat titin isoform expression and cardiomyocyte passive tension.
abstract: Titin is a very large alternatively spliced protein that performs multiple functions in heart and skeletal muscles. A rat strain is described with an autosomal dominant mutation that alters the isoform expression of titin. While wild type animals go through a developmental program where the 3.0 MDa N2B becomes the major isoform expressed by two to three weeks after birth (approximately 85%), the appearance of the N2B is markedly delayed in heterozygotes and never reaches more than 50% of the titin in the adult. Homozygote mutants express a giant titin of the N2BA isoform type (3.9 MDa) that persists as the primary titin species through ages of more than one and a half years. The mutation does not affect the isoform switching of troponin T, a protein that is also alternatively spliced with developmental changes. The basis for the apparently greater size of the giant titin in homozygous mutants was not determined, but the additional length was not due to inclusion of sequence from larger numbers of PEVK exons or the Novex III exon. Passive tension measurements using isolated cardiomyocytes from homozygous mutants showed that cells could be stretched to sarcomere lengths greater than 4 mum without breakage. This novel rat model should be useful for exploring the potential role of titin in the Frank-Starling relationship and mechano-sensing/signaling mechanisms.
authors.affiliation: Muscle Biology Laboratory, University of Wisconsin-Madison, 1805 Linden Drive, Madison, WI 53706, USA. Electronic address: mgreaser@ansci.wisc.edu.
authors.forename: Marion L
authors.initials: ML
authors.lastname: Greaser
authors.affiliation: Muscle Biology Laboratory, University of Wisconsin-Madison, 1805 Linden Drive, Madison, WI 53706, USA.
authors.forename: Chad M
authors.initials: CM
authors.lastname: Warren
authors.affiliation: Muscle Biology Laboratory, University of Wisconsin-Madison, 1805 Linden Drive, Madison, WI 53706, USA.
authors.forename: Karla
authors.initials: K
authors.lastname: Esbona
authors.affiliation: Muscle Biology Laboratory, University of Wisconsin-Madison, 1805 Linden Drive, Madison, WI 53706, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Guo
authors.affiliation: Muscle Biology Laboratory, University of Wisconsin-Madison, 1805 Linden Drive, Madison, WI 53706, USA.
authors.forename: Yingli
authors.initials: Y
authors.lastname: Duan
authors.affiliation: Muscle Biology Laboratory, University of Wisconsin-Madison, 1805 Linden Drive, Madison, WI 53706, USA.
authors.forename: Amanda M
authors.initials: AM
authors.lastname: Parrish
authors.affiliation: Muscle Biology Laboratory, University of Wisconsin-Madison, 1805 Linden Drive, Madison, WI 53706, USA.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Krzesinski
authors.affiliation: Department of Physiology, University of Wisconsin-Madison, 1805 Linden Drive, Madison, WI 53706, USA.
authors.forename: Holly S
authors.initials: HS
authors.lastname: Norman
authors.affiliation: Department of Physiology, University of Wisconsin-Madison, 1805 Linden Drive, Madison, WI 53706, USA.
authors.forename: Sandra
authors.initials: S
authors.lastname: Dunning
authors.affiliation: Department of Physiology, University of Wisconsin-Madison, 1805 Linden Drive, Madison, WI 53706, USA.
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Fitzsimons
authors.affiliation: Department of Physiology, University of Wisconsin-Madison, 1805 Linden Drive, Madison, WI 53706, USA.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Moss
mesh_terms: D017398:Alternative Splicing / Q000235:genetics*; D000818:Animals; D064211:Connectin; D005091:Exons / Q000235:genetics*; D006321:Heart / Q000254:growth & development; D006720:Homozygote; D040542:Mechanotransduction, Cellular / Q000235:genetics; D009124:Muscle Proteins / Q000096:biosynthesis* / Q000235:genetics; D018482:Muscle, Skeletal / Q000378:metabolism; D009154:Mutation; D009206:Myocardium / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D011916:Rats, Inbred F344; D011922:Rats, Mutant Strains; D017207:Rats, Sprague-Dawley; D012518:Sarcomeres / Q000235:genetics / Q000378:metabolism; D020107:Troponin T / Q000096:biosynthesis / Q000235:genetics
chemical_list: D064211:Connectin; D009124:Muscle Proteins; D020033:Protein Isoforms; D020107:Troponin T; C577295:Ttn protein, rat