The Assembly of C. elegans Lamins into Macroscopic Fibers

Shani Deri ¹ Maayan Khayat ² Yosef Gruenbaum ⁴ Ohad Medalia ^2,3 Kfir Ben-Harush kfirb@sce.ac.il ⁵

¹Chemical Engineering, Ariel University, Ariel, Israel
²Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
³Biochemistry, University of Zurich, Zurich, Switzerland
⁴Genetics, The Hebrew University of Jerusalem, Jerusalem, Israel
⁵Chemical Engineering, SCE - Shamoon College of Engineering, Ashdod, Israel

The organization of nuclear lamins into higher-order assemblies within the cell nucleus play a pivotal role in nuclear structure, mechanics and function. The in-vitro investigation of lamins self-assembly into fibrous structures has contributed much to the understanding of lamins hierarchical organization. Information on the mechanical properties of lamin networks assembled in-vitro, however, is still missing. Here, we investigate the mechanics and structure of lamin fibers assembled from C. elegans nuclear lamin (Ce-lamin). Using two fiber-spinning approaches, self-assembly and wet spinning, and cryo electron tomography of vitrified sections, we show that Ce-lamins assemble into macroscopic fibers through the formation of network of paracrystals, which are prominent in vitro structures of lamins. Diversifying the physical properties of lamin-based fibers by protein truncations and point mutations that are known to cause human diseases and alter the structure of paracrystals, in vitro, may produce another tool to investigate the structural-mechanical properties relationship. Accordingly, a point mutation (Q159K), which cause disease in human, and truncations of the `head` and `tail` domains was introduced to Ce-lamin. These variants were tested in various assembly and mechanical testing conditions to produce macroscopic fibers with diverse and unique mechanical properties, such as combination of high plastic strains and intermediate stiffness, and in one case a fiber having superior toughness, comparable to spider silk fiber, which is famous for its amazing toughness. Finally, lamins are part of the intermediate filament (IF) proteins family that except for forming viscoelastic filamentous networks within cells, are also essential parts of various biological materials, such as keratin-based materials. Lamins self-assembly nature and mechanical properties can also make them attractive building blocks for biomimetic and biological materials in diverse applications.