Intranuclear compartments make essential contributions to chromosome structure and function. One such compartment is organized by the nuclear lamina (NL), a protein meshwork that lines the nucleoplasmic surface of the nuclear envelope (NE) in metazoan cells. The NL contains a polymeric assembly of nuclear lamins associated with a large number of transmembrane and peripheral proteins. In addition to serving as a structural framework for the NE, the NL modulates numerous signaling and transcriptional pathways, and provides a tethering and regulatory site for chromatin at the nuclear periphery. The nuclear lamina and associated peripheral heterochromatin can be viewed as comprising a distinctive nuclear compartment, herein termed the nuclear lamina/peripheral chromatin (NL/PC) compartment. Although various components of the NL have been described, the analysis has not been comprehensive. Moreover, approaches are underdeveloped for defining its compositional changes during cell differentiation, and for elucidating the protein-protein interactions that specify the NL network and its chromatin interactions. To address these fundamental issues, this project aims to develop methods to isolate sub-nuclear fractions enriched in the NL/PC compartment from mesenchymal stem cells (MSCs), and from myocytes and adipocytes differentiated from these cells. With the use of these fractions, systematic mass spectrometry (MS) methods will be developed to characterize the protein composition of the NL/PC compartment and to quantitatively chart its changes during differentiation. Chemical crosslinking (XL) combined with MS will be deployed to map the interactions of constituent proteins, and biochemical methods in tandem with super-resolution light microscopy will be used to validate these associations. From implementation of this complementary set of approaches, the project will provide a comprehensive reference map of the NL and the changes that it undergoes during differentiation of defined MSC lineages. This will potentiate the formulation of more general concepts on the functions of the NL/PC compartment, and will identify new components and nodes that can be targeted in future functional studies. This is expected to substantially advance our understanding of the role of the NL in cell-type-specific regulation of peripheral heterochromatin and gene expression.