Elena Scarpa

Chase-and-run between adjacent cell populations promotes directional collective migration

Collective cell migration in morphogenesis and cancer progression often involves the coordination of multiple cell types. How reciprocal interactions between adjacent cell populations lead to new emergent behaviours remains unknown. Here we studied the interaction between neural crest (NC) cells, a highly migratory cell population, and placodal cells, an epithelial tissue that contributes to sensory organs. We found that NC cells chase placodal cells by chemotaxis, and placodal cells run when contacted by NC. Chemotaxis to Sdf1 underlies the chase, and repulsion involving PCP and N-cadherin signalling is responsible for the run. This chase-and-run requires the generation of asymmetric forces, which depend on local inhibition of focal adhesions. The cell interactions described here are essential for correct NC migration and for segregation of placodes in vivo and are likely to represent a general mechanism of coordinated migration.

Cadherin Switch during EMT in Neural Crest Cells Leads to Contact Inhibition of Locomotion via Repolarization of Forces

Summary Contact inhibition of locomotion (CIL) is the process through which cells move away from each other after cell-cell contact, and it contributes to malignant invasion and developmental migration. Various cell types exhibit CIL, whereas others remain in contact after collision and may form stable junctions. To investigate what determines this differential behavior, we study neural crest cells, a migratory stem cell population whose invasiveness has been likened to cancer metastasis. By comparing pre-migratory and migratory neural crest cells, we show that the switch from E- to N-cadherin during EMT is essential for acquisition of CIL behavior. Loss of E-cadherin leads to repolarization of protrusions, via p120 and Rac1, resulting in a redistribution of forces from intercellular tension to cell-matrix adhesions, which break down the cadherin junction. These data provide insight into the balance of physical forces that contributes to CIL in cells in vivo.

Collective cell migration in development.

During embryonic development, tissues undergo major rearrangements that lead to germ layer positioning, patterning, and organ morphogenesis. Often these morphogenetic movements are accomplished by the coordinated and cooperative migration of the constituent cells, referred to as collective cell migration. The molecular and biomechanical mechanisms underlying collective migration of developing tissues have been investigated in a variety of models, including border cell migration, tracheal branching, blood vessel sprouting, and the migration of the lateral line primordium, neural crest cells, or head mesendoderm. Here we review recent advances in understanding collective migration in these developmental models, focusing on the interaction between cells and guidance cues presented by the microenvironment and on the role of cell–cell adhesion in mechanical and behavioral coupling of cells within the collective.

Citron kinase controls abscission through RhoA and anillin

In this report, we confirm that the RhoA-binding protein citron kinase (CIT-K) is required for midbody abscission in late cytokinesis, while it has little or no role in early cytokinesis. Moreover, we show that CIT-K, despite being commonly considered a RhoA effector, promotes midbody stability through RhoA and anillin during late cytokinesis.

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

Summary 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.

The DCR protein TTC3 affects differentiation and Golgi compactness in neurons through specific actin-regulating pathways

In neuronal cells, actin remodeling plays a well known role in neurite extension but is also deeply involved in the organization of intracellular structures, such as the Golgi apparatus. However, it is still not very clear which mechanisms may regulate actin dynamics at the different sites. In this report we show that high levels of the TTC3 protein, encoded by one of the genes of the Down Syndrome Critical Region (DCR), prevent neurite extension and disrupt Golgi compactness in differentiating primary neurons. These effects largely depend on the capability of TTC3 to promote actin polymerization through signaling pathways involving RhoA, ROCK, CIT-N and PIIa. However, the functional relationships between these molecules differ significantly if considering the TTC3 activity on neurite extension or on Golgi organization. Finally, our results reveal an unexpected stage-dependent requirement for F-actin in Golgi organization at different stages of neuronal differentiation.

Actomyosin-driven tension at compartmental boundaries orients cell division independently of cell geometry in vivo

During animal development, planar polarization of the actomyosin cytoskeleton underlies key morphogenetic events such as axis extension and boundary formation. Actomyosin is enriched along compartment boundaries during segmentation of the Drosophila embryo, forming supracellular contractile cables that keep cells segregated at boundaries. Here, we show that these contractile actomyosin cables bias the orientation of division in cells in contact with compartment boundaries. By decreasing actomyosin cable tension locally using laser ablation or, conversely ectopically increasing tension using laser wounding, we demonstrate that localised subcellular force is necessary and sufficient to orient mitoses in vivo. Moreover this bias is independent of cell geometry and involves capture of the spindle pole by the actomyosin cortex.

Suppression of epithelial folding at actomyosin-enriched compartment boundaries downstream of Wingless signalling in Drosophila

ABSTRACT Epithelial folding shapes embryos and tissues during development. Here, we investigate the coupling between epithelial folding and actomyosin-enriched compartmental boundaries. The mechanistic relationship between the two is unclear, because actomyosin-enriched boundaries are not necessarily associated with folds. Also, some cases of epithelial folding occur independently of actomyosin contractility. We investigated the shallow folds called parasegment grooves that form at boundaries between anterior and posterior compartments in the early Drosophila embryo. We demonstrate that formation of these folds requires the presence of an actomyosin enrichment along the boundary cell-cell contacts. These enrichments, which require Wingless signalling, increase interfacial tension not only at the level of the adherens junctions but also along the lateral surfaces. We find that epithelial folding is normally under inhibitory control because different genetic manipulations, including depletion of the Myosin II phosphatase Flapwing, increase the depth of folds at boundaries. Fold depth correlates with the levels of Bazooka (Baz), the Par-3 homologue, along the boundary cell-cell contacts. Moreover, Wingless and Hedgehog signalling have opposite effects on fold depth at the boundary that correlate with changes in Baz planar polarity. Highlighted Article: In the Drosophila embryo, Wingless signalling is required to maintain robust actomyosin enrichment at parasegmental boundaries, and suppresses epithelial folding along these boundaries, where Hedgehog signalling has opposing effects.

Par3/Baz levels control epithelial folding at actomyosin-enriched compartmental boundaries

Epithelial folding is crucial to shape embryos and tissues during development. Here we investigate the coupling between epithelial folding and actomyosin-rich boundaries. The mechanistic relationship between the two is unclear, since actomyosin-rich boundaries can be either associated with folds or not, while epithelial folding has been found to be either dependent or independent of actomyosin contractility. Here we investigate the shallow folds that form at compartmental parasegment boundaries (PSBs) in the early Drosophila embryo. First, we demonstrate that formation of these folds is dependent on the contractility of supracellular actomyosin cables. When the Myosin II phosphatase Flawing is depleted at the PSBs, actomyosin contractility increases, resulting in deeper folds. Conversely, in wingless mutants, actomyosin enrichment and increased contractility at PSBs are lost and this correlates with an absence of folding. Furthermore, when we make ectopic PSBs by expressing Wingless ubiquitously, the ectopic boundaries become enriched in actomyosin and epithelial folds form. Ectopic PSB folds, however, are much deeper than endogenous ones, indicating that epithelial folding is normally under inhibitory control. We present evidence that depletion of Bazooka/Par-3 levels at PSB cell-cell contacts, which is under Wingless signaling control, is responsible for this inhibition. Bazooka is found depleted at endogenous but not ectopic PSBs. In embryos overexpressing Bazooka, endogenous PSB folds form earlier and are much deeper. To ask how local signaling at the boundaries control Bazooka levels at cell-cell contacts, we examined embryos that ectopically expressed Wingless in an hedgehog mutant background. In these embryos, inhibition of folding is rescued, with ectopic PSBs now forming shallow folds as endogenous PSBs. Bazooka is depleted at these ectopic PSBs in absence of Hedgehog, suggesting an opposite effect of Wingless and Hedgehog signaling on Bazooka levels at PSB cell-cell contacts. This uncovers a new role of Bazooka in controlling fold formation at actomyosin-rich compartmental boundaries.