Quantitative cell polarity imaging defines leader-to-follower transitions during collective migration and the key role of microtubule-dependent adherens junction formation

Abstract

The directed migration of cell collectives drives the formation of complex organ systems. A characteristic feature of many migrating collectives is a 'tissue-scale' polarity, whereby 'leader' cells at the edge of the tissue guide trailing 'followers' that become assembled into polarised epithelial tissues en route. Here, we combine quantitative imaging and perturbation approaches to investigate epithelial cell state transitions during collective migration and organogenesis, using the zebrafish lateral line primordium as an in vivo model. A readout of three-dimensional cell polarity, based on centrosomal-nucleus axes, allows the transition from migrating leaders to assembled followers to be quantitatively resolved for the first time in vivo. Using live reporters and a novel fluorescent protein timer approach, we investigate changes in cell-cell adhesion underlying this transition by monitoring cadherin receptor localisation and stability. This reveals that while cadherin 2 is expressed across the entire tissue, functional apical junctions are first assembled in the transition zone and become progressively more stable across the leader-follower axis of the tissue. Perturbation experiments demonstrate that the formation of these apical adherens junctions requires dynamic microtubules. However, once stabilised, adherens junction maintenance is microtubule independent. Combined, these data identify a mechanism for regulating leader-to-follower transitions within migrating collectives, based on the relocation and stabilisation of cadherins, and reveal a key role for dynamic microtubules in this process.

A common framework for EMT and collective cell migration

“…This difference is again reflected by differences in apico-basal polarity, with cells at the front exhibiting a reduction or delocalisation of apico-basal polarity and adhesion proteins, and a loss of tight junctions ( Fig. 2; Revenu and Gilmour, 2009;Revenu et al, 2014). By contrast, cells in the body of the cohort are apicobasally polarised, with mature adherens junctions and desmosomes, but have a much reduced apical membrane and an enlarged basolateral membrane (Hava et al, 2009), similar to the cases mentioned above.…”

Tuning Collective Cell Migration by Cell–Cell Junction Regulation

“…2A,B) (Ghysen and Dambly-Chaudiere 2004). Cells of the primordium express E-cadherin and show foci of the TJ protein ZO1 and aPKC at the center of the tightly packaged primordium (Revenu et al 2014), similar to mature epithelium. On the other hand, cells particularly located at the edge of this cell group display typical mesenchymal characteristics, such as reduced apicobasal polarity and the presence of highly dynamic actin-rich lamellipodia-like protrusions at the basal interactions to the tissue (Lecaudey et al 2008;Hava et al 2009).…”

Noncentrosomal microtubules in C. elegans epithelia

“…Beyond, the contribution of recycling endosomes to junctional targeting will require further investigation. Altogether, the importance of MTs to junctional remodeling is supported by strong genetic data in various models (Brodu et al, 2010;Le Droguen et al, 2015;Meng et al, 2008;Revenu et al, 2014). However, not all junctional proteins strictly depend on MTs for their proper localization: for instance the protein DLG-1, which belongs to the conserved DLG-1/AJM-1-containing complex, remains targeted to adherens junctions when MTs are degraded (Quintin et al, 2016).…”