Functional organization of the nucleus by LEM proteins

In the eukaryotic nucleus lamins and associated proteins form the lamina at the nuclear envelope and complexes in the nucleoplasm. A-type lamins are expressed only in differentiated cells and have important functions in tissue homeostasis and regeneration in the adult organism. Mutations in the LMNA gene give rise to a number of diseases, including muscular dystrophy, lipodystrophy, and premature ageing. The current model suggests that disease-specific lamin mutations interfere structurally and functionally with specific lamin complexes, particularly complexes containing LEM-domain proteins. These proteins are characterized by the presence of the short structural LEM motif , which mediates interaction with chromatin. LEM-domain proteins may therefore be involved in dynamic chromatin organization during cell proliferation and differentiation. The major aims of our study are to functionally analyze the LEM-domain proteins, LAP2alpha and LEM2, which have been shown to interact with lamin A, and to test the hypothesis that they exhibit disease-relevant functions in a complex with A- type lamins. A LAP2alpha knockout mouse model recently developed in our lab puts us in an ideal position for this study. We will generate LAP2alpha -/- cell differentiation models and study the consequences of LAP2alpha knockout on lamin A and nuclear envelope dynamics, on chromatin organization and gene expression in dividing cells and during differentiation. We will also study the interaction of LAP2alpha with chromatin and with novel interaction partners in vitro and in vivo and test the effects of previously generated LAP2alpha mutants showing unregulated or decreased binding to chromatin. In order to relate the observed phenotypes to lamin-linked diseases, we shall also test the hypothesis that some disease-related mutations in lamin A interfere with LAP2alpha association and function. Finally we will study a novel LEM protein, LEM2, aiming at testing the potential functional redundancy with LAP2alpha, by simultaneously knocking down these proteins in various cell systems. Thus, our studies can be expected to reveal molecular mechanisms of nucleoplasmic and peripheral lamin complexes in the functional orgainzation of the nucleus during cell division and differentiation and will also shed light on the molecular basis of lamin-linked human diseases.

In the eukaryotic nucleus lamins and associated proteins form the lamina at the nuclear envelope and complexes in the nucleoplasm. A-type lamins are expressed only in differentiated cells and have important functions in tissue homeostasis and regeneration in the adult organism. Mutations in the LMNA gene give rise to a number of diseases, including muscular dystrophy, lipodystrophy, and premature ageing. The current model suggests that disease-specific lamin mutations interfere structurally and functionally with specific lamin complexes, particularly complexes containing LEM-domain proteins. These proteins are characterized by the presence of the short structural LEM motif , which mediates interaction with chromatin. LEM-domain proteins may therefore be involved in dynamic chromatin organization during cell proliferation and differentiation. The major aims of our study are to functionally analyze the LEM-domain proteins, LAP2alpha and LEM2, which have been shown to interact with lamin A, and to test the hypothesis that they exhibit disease-relevant functions in a complex with A- type lamins. A LAP2alpha knockout mouse model recently developed in our lab puts us in an ideal position for this study. We will generate LAP2alpha -/- cell differentiation models and study the consequences of LAP2alpha knockout on lamin A and nuclear envelope dynamics, on chromatin organization and gene expression in dividing cells and during differentiation. We will also study the interaction of LAP2alpha with chromatin and with novel interaction partners in vitro and in vivo and test the effects of previously generated LAP2alpha mutants showing unregulated or decreased binding to chromatin. In order to relate the observed phenotypes to lamin-linked diseases, we shall also test the hypothesis that some disease-related mutations in lamin A interfere with LAP2alpha association and function. Finally we will study a novel LEM protein, LEM2, aiming at testing the potential functional redundancy with LAP2alpha, by simultaneously knocking down these proteins in various cell systems. Thus, our studies can be expected to reveal molecular mechanisms of nucleoplasmic and peripheral lamin complexes in the functional orgainzation of the nucleus during cell division and differentiation and will also shed light on the molecular basis of lamin-linked human diseases.