Cadherin-6 promotes neural crest cell detachment via F-actin regulation and influences active Rho distribution during epithelial to mesenchymal transition

Abstract

The epithelial-to-mesenchymal transition (EMT) is a complex change in cell phenotype that is important for cell migration, morphogenesis and carcinoma metastasis. Loss of epithelial cell adhesion and tight regulation of cadherin adhesion proteins are crucial for EMT. Cells undergoing EMT often display cadherin switching, where they downregulate one cadherin and induce expression of another. However, the functions of the upregulated cadherins and their effects on cell motility are poorly understood. Neural crest cells (NCCs), which undergo EMT during development, lose N-cadherin and upregulate Cadherin 6 (Cdh6) prior to EMT. Cdh6 has been suggested to suppress EMT via cell adhesion, but also to promote EMT by mediating pro-EMT signals. Here, we determine novel roles for Cdh6 in generating cell motility during EMT. We use live imaging of NCC behavior in vivo to show that Cdh6 promotes detachment of apical NCC tails, an important early step of EMT. Furthermore, we show that Cdh6 affects spatiotemporal dynamics of F-actin and active Rho GTPase, and that Cdh6 is required for accumulation of F-actin in apical NCC tails during detachment. Moreover, Cdh6 knockdown alters the subcellular distribution of active Rho, which is known to promote localized actomyosin contraction that is crucial for apical NCC detachment. Together, these data suggest that Cdh6 is an important determinant of where subcellular actomyosin forces are generated during EMT. Our results also identify mechanisms by which an upregulated cadherin can generate cell motility during EMT.

Should I stay or should I go? Cadherin function and regulation in the neural crest

“…Studies on zebrafish Cadherin-6 revealed that while reduced in the midbrain during EMT (as seen for chick Cadherin-6B), Cadherin-6 is present at low levels in hindbrain neural crest cells both prior to and during their delamination/EMT, a pattern also noted for chick Cadherin-6B (our unpublished data). After EMT, however, Cadherin-6 is not observed in migratory neural crest cells but is instead localized to neuroepithelial cells (Clay & Halloran, 2014). This group also went on to demonstrate, through live imaging in Cadherin-6 morphant embryos, that knockdown of Cadherin-6 precludes neural crest cell EMT by inhibiting the apical detachment of neural crest cells from the neuroepithelium (Figure 1b).…”

Neural crest delamination and migration: Looking forward to the next 150 years

“…In zebrafish, Cadherin-6 is expressed during EMT but in contrast to the chicken embryos, it plays a positive role on EMT. Delamination of fish cephalic NC cells is done by a retraction of the apical pole of the cells and blebbing towards the extracellular matrix (Clay & Halloran, 2013), zebrafish Cadherin-6 controls the activity of the small GTPase Rho during this process (Clay & Halloran, 2014).…”

Cadherin interplay during neural crest segregation from the non‐neural ectoderm and neural tube in the early chick embryo

“…Intriguingly, a number of functional studies suggest that, rather than maintaining epithelial stability among NC cells, Cadherin-6B in chick and Cadherin-6 in fish are required for cells to lose their epithelial junctional polarity and acquire their motile properties (Park and Gumbiner, 2010;Clay and Halloran, 2014). This effect is mediated in chick by non-canonical BMP signaling and in Zebrafish by controlling Rho GTPase distribution in the cytoplasm.…”

“…This effect is mediated in chick by non-canonical BMP signaling and in Zebrafish by controlling Rho GTPase distribution in the cytoplasm. Both signaling pathways ultimately regulate locally the organization of the actin cytoskeleton and promote polarized actomyosin contraction necessary for disruption of apical cell junctions (Park and Gumbiner, 2010;Park and Gumbiner, 2012;Clay and Halloran, 2014). A possible interpretation of these apparently antagonistic functions is that Cadherin-6B would play a dual role in promoting first cell sorting during NC cell specification and maintain their cohesion until delamination while also activating signaling pathways that would act as a negative feedback loop and set the grounds for future delamination.…”