Stefania Bertora

The eukaryotic 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, that occurs through lamins and lamin-associated proteins. Man1 is a member of a lamin-associated protein family characterized by the presence of a highly conserved chromatin-binding domain (LEM). Data obtained with yeast Man1 homolog 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 genomic stability, while in animal models, the function of Man1 has been associated to the regulation of developmental signalling pathways. In this study, truncated mutants of Man1 containing the LEM domain added to Xenopus laevis cell-free extracts were shown to inhibit nuclear assembly and alter nuclear pores formation. Moreover, Xenopus nuclei assembled with 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 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 processes.