Mechanical tugging force regulates the size of cell-cell junctions.

Actomyosin contractility affects cellular organization within tissues in part through the generation of mechanical forces at sites of cell-matrix and cell-cell contact. While increased mechanical loading at cell-matrix adhesions results in focal adhesion growth, whether forces drive changes in the size of cell-cell adhesions remains an open question. To investigate the responsiveness of adherens junctions (AJ) to force, we adapted a system of microfabricated force sensors to quantitatively report cell-cell tugging force and AJ size.

Emergence of patterned stem cell differentiation within multicellular structures.

The ability of stem cells to differentiate into specified lineages in the appropriate locations is vital to morphogenesis and adult tissue regeneration. Although soluble signals are important regulators of patterned differentiation, here we show that gradients of mechanical forces can also drive patterning of lineages. In the presence of soluble factors permitting osteogenic and adipogenic differentiation, human mesenchymal stem cells at the edge of multicellular islands differentiate into the osteogenic lineage, whereas those in the center became adipocytes.

Activation of ROCK by RhoA is regulated by cell adhesion, shape, and cytoskeletal tension.

Adhesion to the extracellular matrix regulates numerous changes in the actin cytoskeleton by regulating the activity of the Rho family of small GTPases. Here, we report that adhesion and the associated changes in cell shape and cytoskeletal tension are all required for GTP-bound RhoA to activate its downstream effector, ROCK. Using an in vitro kinase assay for endogenous ROCK, we found that cells in suspension, attached on substrates coated with low density fibronectin, or on spreading-restrictive micropatterned islands all exhibited low ROCK activity and correspondingly low myosin light chain phosphorylation, in the face of high levels of GTP-bound RhoA.

Microcontact printing: A tool to pattern.

Microcontact printing has proven to be a useful technique in the patterned functionalization of certain chemicals onto surfaces. It has been particularly valuable in the patterning of biological materials. In this review, we describe the basic principles of the technology as well as its use in several applications, with an emphasis on biological ones.

An inhibitory role for FAK in regulating proliferation: a link between limited adhesion and RhoA-ROCK signaling.

Focal adhesion kinase (FAK) transduces cell adhesion to the extracellular matrix into proliferative signals. We show that FAK overexpression induced proliferation in endothelial cells, which are normally growth arrested by limited adhesion. Interestingly, displacement of FAK from adhesions by using a FAK-/- cell line or by expressing the C-terminal fragment FRNK also caused an escape of adhesion-regulated growth arrest, suggesting dual positive and negative roles for FAK in growth regulation.

Shear force at the cell-matrix interface: enhanced analysis for microfabricated post array detectors.

The interplay of mechanical forces between the extracellular environment and the cytoskeleton drives development, repair, and senescence in many tissues. Quantitative definition of these forces is a vital step in understanding cellular mechanosensing. Microfabricated post array detectors (mPADs) provide direct measurements of cell-generated forces during cell adhesion to extracellular matrix.

Nanotechnology for cell-substrate interactions.

In the pursuit to understand the interaction between cells and their underlying substrates, the life sciences are beginning to incorporate micro- and nanotechnology-based tools to probe and measure cells. The development of these tools portends endless possibilities for new insights into the fundamental relationships between cells and their surrounding microenvironment that underlie the physiology of human tissue. Here, we review techniques and tools that have been used to study how a cell responds to the physical factors in its environment.