title: Titin visualization in real time reveals an unexpected level of mobility within and between sarcomeres.
abstract: The giant muscle protein titin is an essential structural component of the sarcomere. It forms a continuous periodic backbone along the myofiber that provides resistance to mechanical strain. Thus, the titin filament has been regarded as a blueprint for sarcomere assembly and a prerequisite for stability. Here, a novel titin-eGFP knockin mouse provided evidence that sarcomeric titin is more dynamic than previously suggested. To study the mobility of titin in embryonic and neonatal cardiomyocytes, we used fluorescence recovery after photobleaching and investigated the contribution of protein synthesis, contractility, and calcium load to titin motility. Overall, the kinetics of lateral and longitudinal movement of titin-eGFP were similar. Whereas protein synthesis and developmental stage did not alter titin dynamics, there was a strong, inhibitory effect of calcium on titin mobility. Our results suggest a model in which the largely unrestricted movement of titin within and between sarcomeres primarily depends on calcium, suggesting that fortification of the titin filament system is activity dependent.
authors.affiliation: Neuromuscular and Cardiovascular Cell Biology, Max-Delbrück-Center for Molecular Medicine (MDC), D-13122 Berlin-Buch, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: da Silva Lopes
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Pietas
authors.forename: Michael H
authors.initials: MH
authors.lastname: Radke
authors.forename: Michael
authors.initials: M
authors.lastname: Gotthardt
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D064211:Connectin; D036681:Fluorescence Recovery After Photobleaching; D005455:Fluorescent Antibody Technique; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D057507:Mice, 129 Strain; D008822:Mice, Transgenic; D018715:Microscopy, Video; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012518:Sarcomeres / Q000378:metabolism*
chemical_list: D064211:Connectin; D009124:Muscle Proteins; D011993:Recombinant Fusion Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D011494:Protein Kinases; D002118:Calcium