Marta Rowińska

Emery–Dreifuss muscular dystrophy type 1 (EDMD1) is a rare genetic disease caused by mutations in the EMD gene, which encodes the nuclear envelope protein emerin. Despite understanding the genetic basis of the disease, the molecular mechanism underlying muscle and cardiac pathogenesis remains elusive. Progress is restricted by the limited availability of patient-derived samples; therefore, there is an urgent need for human-specific cellular models. In this study, we present the generation and characterization of induced pluripotent stem cell (iPSC) lines derived from EDMD1 patients carrying EMD mutations that lead to truncated or absent emerin, together with iPSCs from healthy donor. The patient-specific iPSCs exhibit stable karyotypes, maintain appropriate morphology, express pluripotency markers, and demonstrate the ability to differentiate into three germ layers. To model EDMD1, these iPSCs were differentiated into myogenic progenitors, myoblasts, and multinucleated myotubes, which represent all stages of myogenesis. Each developmental stage was validated by the presence of stage-specific markers, ensuring the accuracy of the model. We present the first iPSC-based in vitro platform that captures the complexity of EDMD1 pathogenesis during myogenesis. This model can significantly contribute to understanding disease mechanisms and develop the targeted therapeutic strategies for EDMD1.

Emery-Dreifuss muscular dystrophy type 1 (EDMD1) is a rare genetic disease caused by mutations in the EMD gene, which encodes the nuclear envelope protein emerin. Despite understanding the genetic basis of the disease, the molecular mechanism underlying muscle and cardiac pathogenesis remains elusive. Progress is restricted by the limited availability of patient-derived samples, therefore there is an urgent need for human-specific cellular models. In this study, we present the generation and characterization of induced pluripotent stem cell (iPSC) lines derived from EDMD1 patients carrying EMD mutations that lead to truncated or absent emerin, together with iPSCs from healthy donor. The patient-specific iPSCs exhibit stable karyotypes, maintain appropriate morphology, express pluripotency markers and demonstrate the ability to differentiate into three germ layers. To model EDMD1, these iPSCs were differentiated into myogenic progenitors, myoblasts and multinucleated myotubes, which represent all stages of myogenesis. Each developmental stage was validated by the presence of stage-specific markers, ensuring the accuracy of the model. We present the first iPSC-based in vitro platform that captures the complexity of EDMD1 pathogenesis during myogenesis. This model can significantly contribute to understanding disease mechanisms and develop the targeted therapeutic strategies for EDMD1.

Lamins and topoisomerases play a critical role in the structural support of cell nuclei, in the regulation of chromatin structure, chromatin distribution, topology of DNA, gene expression, transcription, splicing and transport. Here, we report the role of lamins and Top2 during transition from normal conditions (N), in heat shock (HS) and recovery (R) in Drosophila since the fly genome contains a single gene for B-type lamin (lamin Dm), for A-type lamin (lamin C) and Top2. Heat shock increases transient phosphorylation of lamin Dm on S25, induces changes in solubility of lamin Dm, Top2, HSF, HDAC1 and HP1 proteins, especially in S2 cells and relocates Top2 and chromatin closer to the nuclear lamina with induction of granular staining for Top2 in Kc, S2 and embryonic cells. Lamin Dm interacts with Top2 protein and HS increases the interaction. In vivo photocrosslinking and immunoprecipitation revealed a significant increase in binding to chromatin and nucleic acids upon HS induction for Top2 and lamin Dm. All the detected changes in the properties and location of proteins returned to “normal” after recovery from heat shock. This suggests an important role for lamin Dm, Top2 and their complexes in nuclear functions during HS and recovery. We propose a model in which relocation of Top2 chromatin complexes closer to the nuclear lamina and lamin Dm may help to rearrange the gene expression pattern by tethering HS inactivated genes to nuclear lamina and NPCs which might also help to bind nuclear fraction of non-HS-related transcripts at the nuclear lamina/NPCs area.

Lamin proteins are type V intermediate filament proteins (IFs) located inside the cell nucleus. They are evolutionarily conserved and have similar domain organization and properties to cytoplasmic IFs. Lamins provide a skeletal network for chromatin, the nuclear envelope, nuclear pore complexes and the entire nucleus. They are also responsible for proper connections between the karyoskeleton and structural elements in the cytoplasm: actin and the microtubule and cytoplasmic IF networks. Lamins affect transcription and splicing either directly or indirectly. Translocation of active genes into the close proximity of nuclear lamina is thought to result in their transcriptional silencing. Mutations in genes coding for lamins and interacting proteins in humans result in various genetic disorders, called laminopathies. Human genes coding for A-type lamin (LMNA) are the most frequently mutated. The resulting phenotypes include muscle, cardiac, neuronal, lipodystrophic and metabolic pathologies, early aging phenotypes, and combined complex phenotypes. The Drosophila melanogaster genome codes for lamin B-type (lamin Dm), lamin A-type (lamin C), and for LEM-domain proteins, BAF, LINC-complex proteins and all typical nuclear proteins. The fruit fly system is simpler than the vertebrate one since in flies there is only single lamin B-type and single lamin A-type protein, as opposed to the complex system of B- and A-type lamins in Danio, Xenopus and Mus musculus. This offers a unique opportunity to study laminopathies. Applying genetic tools based on Gal4 and in vitro nuclear assembly system to the fruit fly model may successfully advance knowledge of laminopathies. Here, we review studies of the laminopathies in the fly model system.