IPLS Seminar: Dr Benjamin Friedrich (Physics of Life - Dresden, Germany)

Host: Zena Hadjivasiliou

Abstract: 

Animal movements are powered by contractile myofibrils, millimeter-long acto-myosin bundles that span the entire length of muscle cells with characteristic periodic patterns of micrometer-sized sarcomeres. The physical mechanisms that drive the self-assembly of these “cytoskeletal crystals” are not understood.

I will report a novel mechanisms of controlled “self-rupture” by which new sarcomeres can be added to an existing myofibril that is already under mechanical tension. By combining automatic image analysis of ten-thousand sarcomeres with live imaging of myofibrillogenesis in fast-growing insect flight muscles, we show that sarcomeres can divide into daughter sarcomeres by segregating their myosin filaments along the myofibril axis. This provides a robust mechanism for sarcomere addition, without compromising the structural integrity of pre-tensed myofibrils [Rodier et al., unpublished].

In a second part, I will address the establishment of the first periodic patterns in developing myofibrils. We report data demonstrating that myosin and actin-crosslinking Z-disc proteins form sarcomeric patterns first, while actin becomes polarity-sorted only hours later. This data informs mathematical models of sarcomere self-assembly that are able to replicate periodic sarcomeric patterns, either through non-local interactions between spatially-extended myosin filaments and Z-disc proteins, which bind to an actin scaffold, or catch-bond behavior of the prominent Z-protein a-actinin in response to myosin forces [Kolley et al. PRX Life 2024].