Anillin Regulates Cell-Cell Junction Integrity by Organizing Junctional Accumulation of Rho-GTP and Actomyosin

Abstract

Summary Anillin is a scaffolding protein that organizes and stabilizes actomyosin contractile rings and was previously thought to function primarily in cytokinesis [1–10]. Using Xenopus laevis embryos as a model system to examine Anillin’s role in the intact vertebrate epithelium, we find that a population of Anillin surprisingly localizes to epithelial cell-cell junctions throughout the cell cycle, whereas it was previously thought to be nuclear during interphase [5, 11]. Further, we show that Anillin plays a critical role in regulating cell-cell junction integrity. Both tight junctions and adherens junctions are disrupted when Anillin is knocked down, leading to altered cell shape and increased intercellular spaces. Anillin interacts with Rho, F-actin, and Myosin II [3, 8, 9], all of which regulate cell-cell junction structure and function. When Anillin is knocked down, active Rho (Rho-GTP), F-actin, and Myosin II are misregulated at junctions. Indeed, increased dynamic “flares” of Rho-GTP are observed at cell-cell junctions, while overall junctional F-actin and Myosin II accumulation is reduced when Anillin is depleted. We propose that Anillin is required for proper Rho-GTP distribution at cell-cell junctions and for maintenance of a robust apical actomyosin belt, which is required for cell-cell junction integrity. These results reveal a novel role for Anillin in regulating epithelial cell-cell junctions.

The MgcRacGAP SxIP motif tethers Centralspindlin to microtubule plus ends in Xenopus laevis

“…This abnormal accumulation of the key contractile ring components, F-actin and Myosin II, is likely to drive the cytokinesis defects observed when the Mgc SxIP motif is mutated. This is consistent with previous reports demonstrating cytokinesis failure due to an over-robust RhoA activity zone and/or actomyosin contractile ring ( DeWard and Alberts, 2009;Manukyan et al, 2015;Miller and Bement, 2009;Reyes et al, 2014). Collectively, these data provide in vivo evidence that the Mgc SxIP motif plays a functional role in regulating cytokinesis by mediating the precise localization of Centralspindlin in order for proper localized RhoA activation and accumulation of downstream targets.…”

RhoA regulates actin network dynamics during apical surface emergence in multiciliated epithelial cells

“…Given the requirement for Fmn1 in apical emergence (Sedzinski et al, 2016), we probed the role of RhoA in this process. We first measured the dynamics of RhoA activity using the active RhoA biosensor (rGBD), which has been shown previously to be effective in Xenopus (for examples, see Benink and Bement, 2005;Breznau et al, 2015;Reyes et al, 2014). We expressed GFP-rGBD in the mucociliary epithelium and found that throughout the expansion phase of the MCC apical surface, the fluorescence intensity of normalized active RhoA increased (Fig.…”

Spatial integration of E-cadherin adhesion, signalling and the epithelial cytoskeleton

“…Upon depletion of anillin, pulses of RhoA activation at discrete spots at junctions of Xenopus cells occur with higher frequency, but reduced life-time [90]. Such altered oscillation of active RhoA severely impairs adherens junctions [54,90]. The direct binding of anillin with active RhoA [89] may be a mechanism to maintain spatial and temporal regulation, albeit this has not yet been formally shown.…”

“…Anillin, a bundling protein, interacts with and recruits RhoA to the cytokinesis furrow and cell-cell contacts, where it controls active RhoA localization [89,90]. Upon depletion of anillin, pulses of RhoA activation at discrete spots at junctions of Xenopus cells occur with higher frequency, but reduced life-time [90]. Such altered oscillation of active RhoA severely impairs adherens junctions [54,90].…”