PROJECT SUMMARY The nuclear envelope (NE) has long been thought to function as a static barrier during interphase that regulates interactions between cytosolic proteins and the chromatin. However, recent work challenges this assumption. NE rupture, which results in the transient or permanent loss of nucleus compartmentalization, has been observed in dividing and migrating cells and occurs with increased frequency in cells from laminopathy and cancer patients. Current research has demonstrated that NE rupture can have significant consequences for gene expression, chromatin structure, aneuploidy, and genome stability. However, we have almost no information about the mechanisms driving NE rupture and repair and, thus, we have been unable to rigorously define the cellular consequences. This is due, in part, to our limited understanding of the structure of the NE, particularly lamin network organization, and how structural changes are regulated. The goals of our current research program are 1) to identify the mechanisms of NE rupture and repair, and 2) to develop new tools to analyze NE structure. We plan to achieve these goals by performing a genome-wide RNAi screen in cancer cells to identify regulators of NE stability, and designing new image analysis programs and live-cell imaging reporters to study the 3D dynamics and physical properties of the NE. We are at the beginning of defining the NE as a dynamic structure. Thus, the long-term goals of this research program are to identify the fundamental principles regulating NE dynamics and determine the molecular mechanisms by which defects in NE stability impact disease. Identifying the proteins and pathways that regulate NE rupture and repair will redefine our understanding of NE structure and have broad impacts on associated fields, including chromosome organization and chromatin structure, transcription regulation, cellular responses to mechanical force, and DNA replication and repair, and on larger questions about cell differentiation, tissue development, aging, and cancer initiation and progression.