Final Report Summary - GENESFORCEMOTION (Physical Forces Driving Collective Cell Migration: from Genes to Mechanism)
A variety of fundamental processes in development, health, and disease depend upon the coordinated motion of cell groups. During morphogenesis, for example, the complex architecture of branched organs such as lung, kidney, pancreas, and vasculature is shaped by collective migration of sprouting vessels and ducts. In other developmental processes, clusters of cells are first specified at one location but then travel long distances to the location where they carry out their ultimate biological function. Some of these morphogenetic mechanisms are recapitulated in postnatal life to repair injured tissue. Collective cellular migration also plays a central role devastating diseases such as cancer, as evidenced in histopathological sections of a broad diversity of differentiated carcinomas in which the primary tumor is surrounded by secondary cancer cells that take the form of clusters, chains, and sheets.
To describe coordinated cellular motions in these processes, high-throughput genomic approaches have identified molecular players and mapped their interaction into comprehensive signaling networks. However, detailed signaling and structural information cannot predict collective cellular migration without a physical picture that links cell motion to mechanical stresses exerted within the cell body and at cell-cell boundaries. The main goal of GenesForceMotion was to provide such physical picture and integrate it with patterns of protein expression.
We began by developing novel technologies to map physical forces driving collective cell migration. We first developed Monolayer Traction Force Microscopy to compute forces at the cell-matrix interface from the displacements that cells generate on their underlying soft substrate. Next, we developed Monolayer Stress Microscopy, which computes forces between and within cells by applying rigorous force balance arguments to cell traction forces.
By combining these tools with micropatterning technologies we mapped systematically physical forces and motions during the growth of epithelial sheets. This physiological process revealed unexpected physical features and guidance mechanisms. Firstly, we found that cells within migrating collectives generate highly heterogeneous physical forces that are severe, emerge spontaneously, and ripple across the monolayer. Secondly, within that force landscape, local cellular migrations follow local orientations of maximal principal stress, an unanticipated guidance mechanism we called plithotaxis. Thirdly, we discovered a mechanical wave that propagates slowly to span the monolayer, traversing intercellular junctions in a cooperative manner, and building up differentials of mechanical stress.
We then turned to the study of collective cell migration in the context of gap sealing. By combining force measurements with micropatterning and laser ablation we mapped in time and space the relative contribution of purse string contraction and cell crawling. We showed by direct experimental measurement that these two well-known mechanisms are insufficient to explain force patterns observed during wound closure. We demonstrated a third mechanism of wound closure by which cells compress their underlying substrate by contracting supracellular actomyosin arcs adhered to the matrix through focal adhesions.
Finally we studied the interplay between intercellular adhesion proteins, physical forces, and tissue dynamics. We designed a minimal custom library of validated siRNAs targeting the main molecular components of the intercellular adhesome. For each siRNA perturbation we measured cellular velocities and deformation rates, as well as inter-, intra-, and extra-cellular forces. Using unsupervised clustering analysis, we identified systematic relationships between these physical properties and molecular control modules within the adhesome. Using a cross-validation analysis we established the ability of intercellular adhesion proteins to quantitatively predict tissue dynamics.
To describe coordinated cellular motions in these processes, high-throughput genomic approaches have identified molecular players and mapped their interaction into comprehensive signaling networks. However, detailed signaling and structural information cannot predict collective cellular migration without a physical picture that links cell motion to mechanical stresses exerted within the cell body and at cell-cell boundaries. The main goal of GenesForceMotion was to provide such physical picture and integrate it with patterns of protein expression.
We began by developing novel technologies to map physical forces driving collective cell migration. We first developed Monolayer Traction Force Microscopy to compute forces at the cell-matrix interface from the displacements that cells generate on their underlying soft substrate. Next, we developed Monolayer Stress Microscopy, which computes forces between and within cells by applying rigorous force balance arguments to cell traction forces.
By combining these tools with micropatterning technologies we mapped systematically physical forces and motions during the growth of epithelial sheets. This physiological process revealed unexpected physical features and guidance mechanisms. Firstly, we found that cells within migrating collectives generate highly heterogeneous physical forces that are severe, emerge spontaneously, and ripple across the monolayer. Secondly, within that force landscape, local cellular migrations follow local orientations of maximal principal stress, an unanticipated guidance mechanism we called plithotaxis. Thirdly, we discovered a mechanical wave that propagates slowly to span the monolayer, traversing intercellular junctions in a cooperative manner, and building up differentials of mechanical stress.
We then turned to the study of collective cell migration in the context of gap sealing. By combining force measurements with micropatterning and laser ablation we mapped in time and space the relative contribution of purse string contraction and cell crawling. We showed by direct experimental measurement that these two well-known mechanisms are insufficient to explain force patterns observed during wound closure. We demonstrated a third mechanism of wound closure by which cells compress their underlying substrate by contracting supracellular actomyosin arcs adhered to the matrix through focal adhesions.
Finally we studied the interplay between intercellular adhesion proteins, physical forces, and tissue dynamics. We designed a minimal custom library of validated siRNAs targeting the main molecular components of the intercellular adhesome. For each siRNA perturbation we measured cellular velocities and deformation rates, as well as inter-, intra-, and extra-cellular forces. Using unsupervised clustering analysis, we identified systematic relationships between these physical properties and molecular control modules within the adhesome. Using a cross-validation analysis we established the ability of intercellular adhesion proteins to quantitatively predict tissue dynamics.