Myofibrillogenesis in the developing chicken heart: assembly of Z-disk, M-line and the thick filaments

Abstract

Myofibrillogenesis in situ was investigated by confocal microscopy of immunofluorescently labelled whole mount preparations of early embryonic chicken heart rudiments. The time-course of incorporation of several components into myofibrils was compared in triple-stained specimens, taken around the time when beating starts. All sarcomeric proteins investigated so far were already expressed before the first contractions and myofibril assembly happened within a few hours. No typical stress fibre-like structures or premyofibrils, structures observed in cultured cardiomyocytes, could be detected during myofibrillogenesis in the heart. Sarcomeric proteins like (α)-actinin, titin and actin were found in a defined localisation pattern even in cardiomyocytes that did not yet contain myofibrils, making up dense body-like structures. As soon as the heart started to beat, all myofibrillar proteins were already located at their exact position in the sarcomere. The maturation of the sarcomeres was characterised by a short delay in the establishment of the pattern for M-line epitopes of titin with respect to Z-disk epitopes and the incorporation of the M-line component myomesin, which preceded that of myosin binding protein-C. Thus dense body-like structures, made up of titin, (α)-actinin and actin filaments serve as the first organised complexes also during myofibrillogenesis in situ and titin functions as a ruler for sarcomere assembly as soon as its C termini have become localised. We suggest that assembly of thin and thick filament occurs independently during myofibrillogenesis in situ and that myomesin might be important for integrating thick filaments with the M-line end of titin.

Progressive Myofibril Reorganization of Human Cardiomyocytes on a Dynamic Nanotopographic Substrate

“…By anchoring to the transmembrane integrin, cell focal adhesions are directly affected by external mechano-structural stimuli and then regulate downstream cytoskeletal dynamics. , It has been well documented that focal adhesions play a role in the CMs as the mechano-structural sensor to extracellular changes and transduce the mechanical signals through Z-discs to stabilize the contractile myofibrils. , In our study, disassembly and reassembly of long-stable focal adhesions was the first biological event occurred during hours 4–8, when hiPSC-CMs responded to nanowrinkle formation on the dynamic substrate (Figure k). FAK is the essential signaling machinery of focal adhesion dynamics. − It has been reported that FAK inhibition could enhance the stability of cell focal adhesions to the substrate, and thus promote the assembly of neo-myofibrils. , In our results, Y15-treated hiPSC-CMs obviously recruited large focal adhesion sites on the edge of cells, indicating that FAK inhibition stabilized the costameres consisting of focal adhesions and interconnected Z-discs.…”

“…41,42 It has been well documented that focal adhesions play a role in the CMs as the mechano-structural sensor to extracellular changes and transduce the mechanical signals through Z-discs to stabilize the contractile myofibrils. 43,44 In our study, disassembly and reassembly of long-stable focal adhesions was the first biological event occurred during hours 4−8, when hiPSC-CMs responded to nanowrinkle formation on the dynamic substrate (Figure 3k). FAK is the essential signaling machinery of focal adhesion dynamics.…”

Disruption of Drosophila larval muscle structure and function by UNC45 knockdown

“…Muscle function depends on the proper assembly of the sarcomere. Current models show that sarcomere assembly begins with the development of the Z-discs [1], recruiting proteins such as titin and α-actinin to serve as a scaffold for the integration of thin filaments to form the I-Z-I complex [2][3][4]. The thin filament develops through actin polymerization and troponin integrates with the developing filaments in order to recruit tropomyosin [5].…”

“…The thin filament develops through actin polymerization and troponin integrates with the developing filaments in order to recruit tropomyosin [5]. Myosin filaments are later integrated into this scaffold [2,6]. For each step of sarcomere assembly, molecular chaperones are responsible for incorporating its targeted protein with proper folding [7].…”

Biophysical Reviews “Meet the Editor Series”—Elisabeth Ehler

“…Jean-Claude was another stroke of luck as a supervisor for me, again somebody who had the trust to let people get on with their experiments, while at the same time being absolutely supportive behind the scenes (Ehler et al 2001;Ehler et al 1999). I was hired to run the confocal microscope of the institute, and while I obviously had an extremely good foundation in general fluorescence microscopy from my days in Vic's lab, I had never used a confocal before and had not the slightest idea about the UNIX computers that were used to process the imaging data at the time.…”