ROLE OF NUCLEAR ENVELOPE PROTEIN MAN1 IN NUCLEAR ORGANISATION AND MAINTENANCE OF GENOME STABILITY

The eukaryotic cell nucleus is characterized by a defined spatial organization of the chromatin, which relies on the physical tethering of many genomic loci to the inner surface of the nuclear envelope. This interaction is mainly mediated by lamins and lamin-associated proteins, which create a protein network at the nuclear periphery called nuclear lamina. Man1 is a member of a lamin-associated protein family known as LEM-domain proteins, which are characterized by the presence of a highly conserved domain, called LEM, that mediates the interaction with the chromatin. Data obtained with the yeast Man1 homolog Src1 underline the importance of this protein in different processes of the cell cycle, such as chromosome segregation, nuclear pores assembly, gene expression, chromatin organization and maintenance of genome stability, while in animal models, the function of Man1 has been associated to the regulation of developmental signalling pathways during embryogenesis. In this study, truncated recombinant mutants of Man1, containing the LEM domain, were shown to inhibit nuclear assembly and alter nuclear pore formation when added to Xenopus laevis cell-free extracts. Moreover, Xenopus nuclei assembled in the presence of Man1 truncated fragments were characterized by defects in chromatin organization, DNA replication and accumulation of DNA damage and, as a consequence, they failed to progress through mitosis. Furthermore, mouse embryonic stem cells (mESCs) depleted for Man1 showed evident signs of spontaneous differentiation, indicating inability in the maintenance of stem cell features. Intriguingly, preliminary analysis of Man1-knockout mESCs transcriptional profile showed an alteration of gene expression at the level of pericentromeric and telomeric regions, underlining a potential link between Man1 and genomic stability of these particular regions. In conclusion, this study illustrates the importance of Man1 in ensuring the proper chromatin organization necessary to support different cellular and DNA metabolic processes.