Fibroblasts, immune cells, and cancer cells migrating through pores and fibers in tissue must deform their cell nucleus in order to move. The role of the nuclear protein lamin A/C in limiting nuclear deformation and passage has been studied in pores and microchannels with a smooth contiguous surface. However, cells such as fibroblasts and cancer cells also encounter slender extracellular matrix fibers as they migrate through interstitial tissue. To study this process, we micro-fabricated closely spaced, flexible obstacles with bending rigidity similar to collagen fibers and imaged cell migration around these obstacles. In contrast to its limiting role in nuclear passage through confining channels, lamin A/C facilitated nuclear deformation and passage through fibrous environments because nuclei in lamin-null (Lmna -/-) cells lost their overall morphology and became entangled around the obstacles. We propose that, analogous to surface tension-mediated deformation of a liquid drop, lamin A/C imparts a surface tension on the nucleus preventing nuclear entanglement and allowing nuclear passage through fibrous environments. We investigated a related long-standing question of how the cell shapes the nucleus in migrating cells. We cultured cells on surfaces with micro-patterned fibronectin such that narrow fibronectin lines (5 microns in width) culminated into wider rectangles. Nuclei in cells on 1-D lines had folds in the nuclear lamina, which disappeared as the cells migrated onto the 2-D rectangles and the nucleus reached a steady-state shape. These data confirmed the prediction of our previously proposed model that the resistance to nuclear shape changes in low so long as there are folds in the nuclear lamina. We also validated another model prediction- that the nuclear surface should move in response to local cell protrusions - through dynamic vertical imaging and tracking of protrusions and nuclear shapes in breast cancer cells. To address the errors in vertical imaging in these studies due to the well-known phenomenon of refractive index mismatch, we developed a new approach for improved imaging of the x-z cross-section of fluorescent samples. Finally, we reported the discovery that Barrier-to-autointegration Factor (BAF) mediates the repair of the nuclear envelope after nuclear envelope rupture during confined cell migration.
