Dynamics of Multicellular Aggregation and Disaggregation: Implications for Tissue Engineering and Cancer Metastasis

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Epithelial tissues play an important physiological role. Tightly cohesive epithelial sheets form protective barriers that line organs, and in addition, fold into a wide variety of complex 3D architectures with specialized functions. A key facet of tissue morphogenesis involves the aggregation of similar cells into cohesive groups. Here, we have analyzed the dynamics of aggregation using quantitative imaging techniques (Chapter II). We show that multicellular aggregation dynamics adhere to a transport-reaction model that is broadly appreciated for physicochemical systems. This model of aggregation dynamics differs from the classical equilibrium paradigm of cell aggregation based on differential adhesivity of cells to neighboring cells versus the underlying substratum. Our findings reveal a previously unrecognized role for cell motility during developmental aggregation processes and provide design principles for promoting cell aggregation dynamics in contexts such as tissue engineering that are distinct from the currently accepted paradigm. Multicellular aggregation is reversible. In fact, the break-up of multicellular clusters (“cell scatter”) is not only important for developmental processes, but also contributes to metastasis. However, current molecular genetics studies of cell scatter are predominantly qualitative and do not provide a quantitative assessment of the relative strengths of molecular signals in inducing cell scatter. By developing and implementing an automated image processing algorithm, we quantify two aspects of cell scatter – the breakdown of cell-cell adhesions and the dispersion of detached cells – in mammary epithelial cells treated with different combinations of biochemical cues (Chapter III). We demonstrate that our metrics of cell scatter identify the effects of individual cues and detect synergies between them. We envision that this approach will be useful for mapping the relative potencies of regulators of cell scatter and may guide therapeutic strategies. Multicellular processes such as aggregation and scatter involve molecular-level changes within cell-cell adhesions. To complement imaging-based strategies at the cellular and multicellular levels, we developed a quantitative microtiter assay for examining the expression of cell-cell adhesion proteins and associations between them (Chapter IV). Using two case studies related to cancer biology, we demonstrate that our assay provides a more detailed quantitative picture of molecular changes within epithelial adhesive structures, which can provide added insight into the regulation of morphogenetic events.