An unstable crust-like network under construction – ScienceDaily


During development, the cells of the fetus divide until a fully functioning organism appears. One component of the cell is particularly important during this process: the cell cortex. This fine network of hair-like filamentous structures (called actin) just below the cell membrane is the main determinant of cell shape and is involved in almost everything the cell does, such as movement, division, or sensing its environment. However, the cortex must first be built of single molecules, and if it is not built correctly, the cells of an organism will never get to the right place to perform their functions.

An international team of researchers from the Max Planck Institute for Molecular Cell Biology and Genetics (MPI-CBG) in Dresden, the Max Planck Institute for the Physics of Complex Systems (MPI-PKS), and the Physics of Life Distinguished Group (PoL) at TU Dresden has studied the formation of a dynamic cell cortex. This is in the roundworm Certain types are elegant. They found that thousands of dynamic, short-lived, droplet-like condensers formed by actin filaments control the generation of the first cortex, the time an unfertilized egg cell passes into an embryo after fertilization. The principles revealed in this study help to understand how the formation of cellular structures is controlled.

Immediately after the fertilization of the egg cell, the formation of the cell shell begins and it takes about ten minutes for it to fully form. The cortex consists of actin filaments and motor proteins, which are organized into a dense interlocking network. Cortical dynamics stem from motor proteins that pull on actin filaments, generating stresses that lead to cortical tension. This cortical tension drives, for example, the shape of cells, their ability to sense their environment, and their ability to function in our bodies. The dynamics of the cell cortex have been intensively studied in the past, but the mechanism by which the cell cortex is first activated immediately after fertilization is unknown. It is crucial to understand the principles underlying cell cortex formation because it is involved in nearly every function of the cell, and improper cortical organization impairs key cellular and developmental processes.

Protein thickeners have a short life and ensure proper development

To explore how the cell cortex is activated, a multidisciplinary team of researchers at MPI-CBG, MPI-PKS and PoL studied this process in the roundworm. C. elegans. “We were able to observe how the actin and actin core proteins WSP-1 and ARP2/3 came together to form condensers that lasted only seconds, only to disassemble immediately afterwards. These condensers ensure that the right amount of actin filaments are present and that they are connected in just the right way. For me, the The beauty of these structures, which are made of highly branched actin filaments, like a snowflake, lies in what their dynamics teach us about the unconventional chemistry of living matter,” explains Arjun Narayanan, one of the study’s lead authors and researcher in Stefan Grill, Director of MPI-CBG. Victoria Tianjin Yan, another lead author, continues, “We developed our own imaging and image analysis method, called mass balance imaging, to study how the structure of short-lived capacitors grows and develops.” During their study, the researchers found that internal chemical reactions control how quickly the capacitor grows and when it contracts. Thus, cortical condensate strongly regulates its life cycle, largely independent of its external environment.

Stefan Grill summarizes, “We conclude that condensers in the cell cortex represent a new type of biomolecular condensate driven by specific chemical reactions to assemble and disassemble within seconds.” “We propose that these short-lived condensers control the activation of the cell cortex and the fine-tuning of its growing structure after fertilization,” he adds. C. elegans Egg. Frank Gulisher, MPI-PKS Director and another supervising author, adds, “This study is another example of linking physics and biology here in Dresden. Our interactive environment with biologists and theoretical physicists together includes new, interdisciplinary approaches to unraveling the physics of biology processes.”



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