Condensin II mediated interphase chromosome compaction drive changes in nuclear architecture. Julianna Bozler¹, Huy Nguyen¹, Tom Hartl², Christopher Bauer², Gregory Rogers², Giovanni Bosco¹. 1) Geisel School of Medicine, Dartmouth College, Hanover, NH; 2) Molecular and Cellular Biology, University of Arizona, Tucson, AZ.

   In eukaryotic cells, the nuclear membrane is an essential component of cellular organization and highly dynamic through the cell cycle. Despite its loss of structural stability during early cell replication steps, the maintenance of its structure during interphase is important for normal cell function. Given the vital role of this structure, it is not surprising that aberrant nuclear envelope morphologies are characteristic of many human diseases, such as progeria. Additionally, recent evidence suggests the nuclear membrane plays an important role in the establishment and maintenance of chromosome arrangement in the interphase nucleus. We have investigated the relationship between the nuclear envelope and the 3-dimensional organization of chromatin. We show that Drosophila condensin II provides a chromatin compaction activity in interphase cells, and this condensation force can drive distortions in nuclear architecture that include invaginations of the envelope and intra-nuclear vesicle formation. Vesicles inside the nucleus contain nuclear pore proteins, suggesting that proteins integral to nuclear membrane are force into the interior of the nucleus. We propose a model where chromatin tethers to inner nuclear envelope proteins serve as anchors that allow interphase chromosome movements to cause morphological changes of the nuclear envelope. We speculate that interphase chromatin compaction may be a normal mechanism that reorganizes nuclear architecture, while under pathological conditions, such as laminopathies, these compaction forces contribute to dramatic defects in nuclear morphology.