The Role of Excess Nuclear Laminar Area in Confined Migration

Abstract

Cell migration is an important process for functions such as immune response and wound healing. It also plays an important role in the metastatic spread of cancer. Migration occurs through pores of various sizes depending on the tissue, and cells must deform the nucleus to allow for such passage. The nucleus has excess surface area in the lamina - defined as the area over that of a sphere of the same volume - which shows up as wrinkles when the overall nuclear shape is rounded. As the cell tries to pass through a confining space, the lamina unwrinkles and smoothens out. In the first part of this thesis, we investigate the role of the nuclear lamina in limiting cell migration through constrictions, and our results suggest that nuclei with insufficient excess area cannot migrate through our constricting channels. The yes-associated protein (YAP) is a mechanosensitive transcriptional coactivator that plays a critical role in cell proliferation, regulation of organ size, and tumorigenesis. YAP activation, measured by increased translocation to the nucleus, is positively correlated with many types of cancers. Nuclear flattening, using atomic force cantilevers, has been shown to be sufficient to induce the nuclear import of YAP. In the second part of this thesis, we aim to understand if the forces experienced by a cell during confined migration also lead to activation of YAP, quantified as the nuclear to cytoplasmic ratio. We observe that cells in confinement have a lower nuclear to cytoplasmic ratio than cells that are unconfined between constrictions as well as cells spread on glass. Our hypothesis is that cellular forces that significantly deform the nucleus in constrictions do not promote YAP activation likely because the lamina has not unwrinkled fully and so there is no tension across the nuclear lamina. Further experiments with a tension-sensing probe are required to test this hypothesis.