The Ric-8A/Gα13/FAK signalling cascade controls focal adhesion formation during neural crest cell migration in Xenopus.

Ric-8A is a pleiotropic guanine nucleotide exchange factor involved in the activation of various heterotrimeric G-protein pathways during adulthood and early development. Here, we sought to determine the downstream effectors of Ric-8A during the migration of the vertebrate cranial neural crest (NC) cells. We show that the Gα13 knockdown phenocopies the Ric-8A morphant condition, causing actin cytoskeleton alteration, protrusion instability, and a strong reduction in the number and dynamics of focal adhesions. In addition, the overexpression of Gα13 is sufficient to rescue Ric-8A-depleted cells. Ric-8A and Gα13 physically interact and colocalize in protrusions of the cells leading edge. The focal adhesion kinase FAK colocalizes and interacts with the endogenous Gα13, and a constitutively active form of Src efficiently rescues the Gα13 morphant phenotype in NC cells. We propose that Ric-8A-mediated Gα13 signalling is required for proper cranial NC cell migration by regulating focal adhesion dynamics and protrusion formation.

Redistribution of Adhesive Forces through Src/FAK Drives Contact Inhibition of Locomotion in Neural Crest.

Contact inhibition of locomotion is defined as the behavior of cells to cease migrating in their former direction after colliding with another cell. It has been implicated in multiple developmental processes and its absence has been linked to cancer invasion. Cellular forces are thought to govern this process; however, the exact role of traction through cell-matrix adhesions and tension through cell-cell adhesions during contact inhibition of locomotion remains unknown. Here we use neural crest cells to address this and show that cell-matrix adhesions are rapidly disassembled at the contact between two cells upon collision. This disassembly is dependent upon the formation of N-cadherin-based cell-cell adhesions and driven by Src and FAK activity. We demonstrate that the loss of cell-matrix adhesions near the contact leads to a buildup of tension across the cell-cell contact, a step that is essential to drive cell-cell separation after collision.

Michael Abercrombie: contact inhibition of locomotion and more.

Michael Abercrombie is regarded as one of the principal pioneers of cell biology. Although Abercrombie began his career as an experimental embryologist, working on the avian organizer with C. H. Waddington, questions on how cells in culture migrate and interact dominated his career. Whilst studying the social behaviour of chick heart embryonic fibroblasts, Abercrombie identified a phenomenon whereby colliding cells collapse their protrusions towards the cell-cell contact upon a collision, preventing their continued migration. The cells then form protrusions away from the contact and, space permitting, migrate away from each other. This behaviour is now referred to as 'contact inhibition of locomotion' and has been identified within embryology as the driving force behind the directional migration of the neural crest and the dispersion patterning of haemocytes and Cajal-Retzius neurons. Furthermore, its loss between collisions of cancer cells and healthy cells is associated with metastasis. In this review we begin with an overview of Abercrombie's life and highlight some of his key publications. We then discuss Abercrombie's discovery of contact inhibition of locomotion, the roles which cell-cell adhesions, cell-matrix adhesions and the cytoskeleton play in facilitating this phenomenon, and the importance of contact inhibition of locomotion within the living organism.

Molecular basis of contact inhibition of locomotion.

Contact inhibition of locomotion (CIL) is a complex process, whereby cells undergoing a collision with another cell cease their migration towards the colliding cell. CIL has been identified in numerous cells during development including embryonic fibroblasts, neural crest cells and haemocytes and is the driving force behind a range of phenomenon including collective cell migration and dispersion. The loss of normal CIL behaviour towards healthy tissue has long been implicated in the invasion of cancer cells. CIL is a multi-step process that is driven by the tight coordination of molecular machinery. In this review, we shall breakdown CIL into distinct steps and highlight the key molecular mechanisms and components that are involved in driving each step of this process.

Forcing contact inhibition of locomotion.

Contact inhibition of locomotion drives a variety of biological phenomenon, from cell dispersion to collective cell migration and cancer invasion. New imaging techniques have allowed contact inhibition of locomotion to be visualised in vivo for the first time, helping to elucidate some of the molecules and forces involved in this phenomenon.

A novel method to study contact inhibition of locomotion using micropatterned substrates.

The concept of contact inhibition of locomotion (CIL) describes the ability of a cell to change the direction of its movement after contact with another cell. It has been shown to be responsible for physiological and developmental processes such as wound healing, macrophage dispersion and neural crest cell migration; whereas its loss facilitates cancer cell invasion and metastatic dissemination. Different assays have been developed to analyze CIL in tissue culture models. However, these methods have several caveats. Collisions happen at low frequency between freely migrating cells and the orientation of the cells at the time of contact is not predictable. Moreover, the computational analysis required by these assays is often complicated and it retains a certain degree of discretion. Here, we show that confinement of neural crest cell migration on a single dimension by using a micropatterned substrate allows standardized and predictable cell-cell collision. CIL can thus easily be quantified by direct measurement of simple cellular parameters such as the distance between nuclei after collision. We tested some of the signaling pathways previously identified as involved in CIL, such as small GTPases and non-canonical Wnt signaling, using this new method for CIL analysis. The restricted directionality of migration of cells in lines is a powerful strategy to obtain higher predictability and higher efficiency of the CIL response upon cell-cell collisions.