The Wnt signaling pathway can be grouped into two classes, the β-catenin-dependent and β-catenin-independent pathways. Wnt5a signaling through a β-catenin-independent pathway promotes microtubule (MT) remodeling during cell-substrate adhesion, cell migration, and planar cell polarity formation. Although Wnt5a signaling and MT remodeling are known to form an interdependent regulatory loop, the underlying mechanism remains unknown. Here we show that in HeLa cells, the paralogous MT-associated proteins Map7 and Map7D1 (Map7/7D1) form an interdependent regulatory loop with Disheveled, the critical signal transducer in Wnt signaling. Map7/7D1 bind to Disheveled, direct its cortical localization, and facilitate the cortical targeting of MT plus-ends in response to Wnt5a signaling. Wnt5a signaling also promotes Map7/7D1 movement toward MT plus-ends, and depletion of the Kinesin-1 member Kif5b abolishes the Map7/7D1 dynamics and Disheveled localization. Furthermore, Disheveled stabilizes Map7/7D1. Intriguingly, Map7/7D1 and its ortholog, Ensconsin show planar-polarized distribution in both mouse and fly epithelia, and Ensconsin influences proper localization of Disheveled in pupal wing cells. These results suggest that the role of Map7/7D1/Ensconsin in Disheveled localization is evolutionarily conserved.

In contrast to extracellular chemotactic gradients, how cell-adhesion molecules contribute to directing cell migration remains more elusive. Here we studied the collective migration of Drosophila larval epidermal cells (LECs) along the anterior-posterior axis and propose a migrating cell group-autonomous mechanism in which an atypical cadherin Dachsous (Ds) plays a pivotal role. In each abdominal segment, the amount of Ds in each LEC varied along the axis of migration (Ds imbalance), which polarized Ds localization at cell boundaries. This Ds polarity was necessary for coordinating the migratory direction. Another atypical cadherin, Fat (Ft), and an unconventional myosin Dachs, both of which bind to Ds, also showed biased cell-boundary localizations, and both were required for the migration. Altogether, we propose that the Ds imbalance within the migrating tissue provides the directional cue and that this is decoded by Ds-Ft-mediated cell-cell contacts, which restricts lamellipodia formation to the posterior end of the cell.

The molecular mechanisms by which cilia orientation is coordinated within and between multiciliated cells (MCCs) are not fully understood. In the mouse oviduct, MCCs exhibit a characteristic BB orientation and microtubule gradient along the tissue axis. The intracellular polarities were moderately maintained in the cells lacking CELSR1, a planar cell polarity (PCP) factor involved in tissue polarity regulation, although the intercellular coordination of the polarities was disrupted. Whereas CAMSAP3, a microtubule minus-end regulator, is found to be critical for determining the intracellular BB orientation. CAMSAP3 localized to the base of cilia in a polarized manner, and its mutation led to the disruption of intracellular coordination of BB orientation as well as the assembly of microtubules interconnecting BBs without affecting PCP factor localization. Thus, both CELSR1 and CAMSAP3 are responsible for BB orientation but in distinct ways; their cooperation should thus be critical for generating functional multiciliated tissues.

No abstract