Mobility is vital for all animals. Striated muscles, allow animals to voluntarily move as well as involunteered movement of the cardiac muscle. This is achieved by converting chemical energy into mechanical one. The smallest contractile subunit of striated muscles is called the sarcomere. The boundaries between each sarcomere are called Z-disc. [1,2] They allow force transmission and are also a hub for cell signaling. These functions are possible thanks to a plethora of proteins that interact with each other in a highly ordered manner, appearing almost paracrystalline. [1] In this project we want to contribute to a better understanding of myofibrilogenesis the process in which the sarcomeres form. According to the premyofibril theory, the myofibrillogenesis starts from small punctate structures, called Z-bodies, which fuse laterally together. [3-5] Recently we discovered that one of the Z-Body associated Proteins, FATZ-1, can undergo Liquid-liquid phase separation (LLPS) [6], raising for the first time the question of whether FATZ‐1 can create an interaction hub for Z‐disk proteins through membrane‐less compartmentalization during the initial stages of sarcomere assembly. Experiments to answer this question proved that FATZ-1 droplets have liquid-like properties in vitro and that α-actinin 2 is colocalizes and is enriched in those droplets. Furthermore, α-actinin 2 alter the phase diagram of the droplets by the size and even dissolving them, indicating a regulatory mechanism. [6] Recently, the group of Travis Hinson was able to generate a cell model with human induced pluripotent stem cell cardiomyocytes (hiPSC-CM´s) in which they observed Z-Bodies upon troponin T knock out. [7] This project aims not only to expand our study on the localization and influence of the other Z-bodies protein on FATZ-1 phase separation but also to prove this hypothesis in vivo. Unrevealing how such a highly ordered structure like the Z-Disc emerges would lead to a better understanding of how muscles actually form on a molecular level and may reveal how pathogenic protein variants lead to myopathies.
1. Luther, P. K. (2009). The vertebrate muscle Z-disc: Sarcomere anchor for structure and signalling. Journal of Muscle Research and Cell Motility, 30(5–6), 171–185. https://doi.org/10.1007/s10974-009-9189-6
2. Gautel M, Djinović-Carugo K. The sarcomeric cytoskeleton: from molecules to motion. J Exp Biol. 2016 Jan;219(Pt 2):135-45. doi: 10.1242/jeb.124941. PMID: 26792323.
3. Sanger, J. W., Kang, S., Siebrands, C. C., Freeman, N., Du, A., Wang, J., Stout, A. L., & Sanger, J. M. (2005). How to build a myofibril. Journal of Muscle Research and Cell Motility, 26(6–8), 343–354. https://doi.org/10.1007/s10974-005-9016-7
4. Stout, A. L., Wang, J., Sanger, J. M., & Sanger, J. W. (2008). Tracking changes in Z-band organization during myofibrillogenesis with FRET imaging. Cell Motility and the Cytoskeleton, 65(5), 353–367. https://doi.org/10.1002/cm.20265
5. Sanger, J. W., Wang, J., Fan, Y., White, J., & Sanger, J. M. (2010). Assembly and dynamics of myofibrils. In Journal of Biomedicine and Biotechnology (Vol. 2010). https://doi.org/10.1155/2010/858606
6. Sponga, A., Arolas, J. L., Schwarz, T. C., Jeffries, C. M., Rodriguez Chamorro, A., Kostan, J., Ghisleni, A., Drepper, F., Polyansky, A., de Almeida Ribeiro, E., Pedron, M., Zawadzka-Kazimierczuk, A., Mlynek, G., Peterbauer, T., Doto, P., Schreiner, C., Hollerl, E., Mateos, B., Geist, L., … Djinović-Carugo, K. (2021). Order from disorder in the sarcomere: FATZ forms a fuzzy but tight complex and phase-separated condensates with -actinin. In Sci. Adv (Vol. 7). https://www.science.org
7. Ladha, F. A., Thakar, K., Pettinato, A. M., Legere, N., Ghahremani, S., Cohn, R., Romano, R., Meredith, E., Chen, Y. S., & Hinson, J. T. (2021). Actinin BioID reveals sarcomere crosstalk with oxidative metabolism through interactions with IGF2BP2. Cell Reports, 36(6). https://doi.org/10.1016/j.celrep.2021.109512