FD curves were plotted as the deflection of the cantilever as it was lowered in the em z /em -axis to make contact with, and compress single cells

FD curves were plotted as the deflection of the cantilever as it was lowered in the em z /em -axis to make contact with, and compress single cells. separation in to directly evaluate the role of these various parameters. We find that ephrin-Eph-based repulsion is very effective at inducing and maintaining separation, whereas differences in adhesion or contractility have surprisingly little impact. Computer simulations support and generalise our experimental results, showing that a high heterotypic interfacial tension between tissues is key to their segregation. We propose a unifying model, in which conditions of sorting previously considered as driven by differential adhesion/tension should be viewed as suboptimal cases of heterotypic interfacial tension. Introduction Physical separation of embryonic cell populations is fundamental to metazoan development. The process, which results in the sharp delimitation of cell masses by so-called tissue boundaries, appears to rely on the ability of individual cells to distinguish between homotypic contacts, i.e. contacts with cells of the same type, and heterotypic contacts with cells of a different type. This property can be shown by mixing dissociated cells from different embryonic regions and observing their progressive sorting into separate groups. These observations led Holtfreter to propose the concept of selective cell affinities1, 2. Four major models have attempted to explain the elusive nature of these affinities: the differential adhesion hypothesis (DAH)3 stated that different cell types would sort according to their respective intercellular adhesive strength to maximise the number of adhesive complexes formed. In the differential interfacial tension hypothesis (DITH), Brodland4, 5 introduced contractility of the cortical actomyosin cytoskeleton as an essential parameter of cellCcell interactions. Tenants of the DITH have argued that tissue differences in cortical tension are Rocuronium bromide the major driver of tissue separation6, 7. The selective adhesion hypothesis (SAH) proposes that tissue segregation is due to the expression of unique sets of cadherins, which are considered to bind homophilically8, 9. Lastly, cell surface cues, such as ephrin ligands and Eph receptors have been involved in the generation of repulsive reactions at heterotypic contacts (reviewed in ref. 10). At the cellular level, these reactions are characterised by a local increase in cortical actomyosin contractility, and consequently destabilisation/disruption of cell adhesion at heterotypic contacts11. These four models can be expressed and directly compared using the concept of interfacial tension4, 5 (Fig.?1a). Note that to avoid ambiguities, we prefer to use the term contact tension and reserve the term interfacial tension to the tension at tissue interfaces12, 13 (Fig.?1b). DAH and DITH can be expressed by a similar configuration, where the tension at homotypic contacts is higher in one of the two cell populations and intermediate at heterotypic contacts (Fig.?1c). Ephrin-Eph-mediated repulsion creates a different situation, where tension is strongly increased at heterotypic contacts compared to homotypic contacts inside the tissues (Fig.?1c). We call this configuration high heterotypic interfacial Rabbit Polyclonal to MRIP tension (HIT). Most experimental data support ephrin-Eph-dependent HIT as the major mechanism for separation in vertebrates10, 14C22, and evidence for HIT has also been found in has turned out surprisingly resistant to manipulations of cadherin levels26, 27. Alternatively, adhesive and tensile properties may be participating in separation by reinforcing repulsion-based separation. CellCcell adhesion and ephrin-Eph signalling are indeed involved in an intimate interplay: we Rocuronium bromide have shown that a proper balance between ephrin-Eph signalling, and adhesion is crucial in setting the threshold required for overt cell Rocuronium bromide detachments, both at the tissue boundary interface and within the tissues20, 21. Thus, the impact of adhesive and contractile differences on tissue separation remains unclear. In ectoderm and mesoderm and their adhesive and contractile properties. a Diagram of the early gastrula indicating the regions used as the source for tissue explants. Induced mesoderm was produced by expression of -catenin (-cat) and constitutively active Activin receptor (caActR) in the blastocoel roof (or and point to the mature (and corresponding value), and min and max values without outliers (symbolises the actomyosin cortex. A curved cellCcell interface reflects unequal Ct A and Ct B tensions. b Examples of homotypic and heterotypic doublets, expressing.