A lamin A/C variant causing striated muscle disease provides insights into filament organization

• Published in: Journal of cell science Vol. 134; no. 6
• Main Authors: Kronenberg-Tenga, Rafael, Tatli, Meltem, Eibauer, Matthias, Wu, Wei, Shin, Ji-Yeon, Bonne, Gisèle, Worman, Howard J., Medalia, Ohad
• Format: Journal Article
• Language: English
• Published: England The Company of Biologists Ltd 22.03.2021
• Subjects: Animals; Cytoskeleton; Lamin Type A - genetics; Lamin Type B - genetics; Mice; Muscle, Striated; Mutation - genetics; Nuclear Lamina; Lamins; Intermediate filaments; Cryo-electron tomography
• ISSN: 0021-9533; 1477-9137; 1477-9137
• DOI: 10.1242/jcs.256156

The LMNA gene encodes the A-type lamins, which polymerize into ∼3.5-nm-thick filaments and, together with B-type lamins and associated proteins, form the nuclear lamina. Mutations in LMNA cause a wide variety of pathologies. In this study, we analyzed the nuclear lamina of embryonic fibroblasts from LmnaH222P/H222P mice, which develop cardiomyopathy and muscular dystrophy. Although the organization of the lamina appeared unaltered, there were changes in chromatin and B-type lamin expression. An increase in nuclear size and consequently a relative reduction in heterochromatin near the lamina allowed for a higher resolution structural analysis of lamin filaments using cryo-electron tomography. This was most apparent when visualizing lamin filaments in situ and using a nuclear extraction protocol. Averaging of individual segments of filaments in LmnaH222P/H222P mouse fibroblasts resolved two polymers that constitute the mature filaments. Our findings provide better views of the organization of lamin filaments and the effect of a striated muscle disease-causing mutation on nuclear structure.