Septin-dependent remodeling of cortical microtubule drives cell reshaping during epithelial wound healing

Abstract

Wounds in embryos heal rapidly through contraction of the wound edges. Despite well-recognized significance of the actomyosin purse string for wound closure, roles for other cytoskeletal components are largely unknown. Here, we report that the septin cytoskeleton cooperates with actomyosin and microtubules to coordinate circumferential contraction of the wound margin and concentric elongation of wound-proximal cells in embryos. Microtubules reoriented radially, forming bundles along lateral cell cortices in elongating wound-proximal cells. Depletion of septin 7 (Sept7) slowed wound closure by attenuating the wound edge contraction and cell elongation. ROCK/Rho-kinase inhibitor-mediated suppression of actomyosin contractility enhanced the Sept7 phenotype, whereas the Sept7 depletion did not affect the accumulation of actomyosin at the wound edge. The cortical microtubule bundles were reduced in wound-proximal cells in Sept7 knockdown (Sept7-KD) embryos, but forced bundling of microtubules mediated by the microtubule-stabilizing protein Map7 did not rescue the Sept7-KD phenotype. Nocodazole-mediated microtubule depolymerization enhanced the Sept7-KD phenotype, suggesting that Sept7 is required for microtubule reorganization during cell elongation. Our findings indicate that septins are required for the rapid wound closure by facilitating cortical microtubule reorganization and the concentric elongation of surrounding cells.

Novel Functions of the Septin Cytoskeleton

“…43 The functional relevance of these septin-microtubule interactions was highlighted by the findings that either SEPT2, or SEPT7 depletion disrupts different microtubule populations in polarized and migrating epithelial cells. 44,45 It should be noted that the ability of septins to form multiprotein complexes is not limited to their oligomerization and interactions with actin filaments and microtubules. Published interactomes of different septin family members show a large variety of additional binding partners that include actin-binding proteins, regulators of vesicle trafficking, and signaling molecules such as kinases, phosphatases, and small GTPases.…”

“…Several studies demonstrate that loss of SEPT2, SEPT7, and SEPT9 consistently attenuates wound healing in cultured epithelial and cancer cell monolayers, as well as in Xenopus embryo. 37,45,59,60 The observed promigratory activity of the septin cytoskeleton may be mediated by different mechanisms such as control of cortical microtubule assembly at the migrating cell edge, 45 formation of basal actin-based stress fibers, 37 stabilization of focal adhesions, 37,59 and activation of mitogen-activated protein (MAP) kinase signaling. 60 Interestingly, SEPT2 and SEPT9 are not only essential for focal adhesion maturation, but also regulate the assembly of other adhesion structures (such as podosomes), that mediate matrix degradation.…”

Forceful closure: cytoskeletal networks in embryonic wound repair

“…In Drosophila embryos, microtubules are present within filopodial protrusions at wound edges (Abreu-Blanco et al , 2012), where they may provide pushing force and facilitate the transport of adhesion receptors or guidance cues along the protrusion (Figure 3, cyan). In addition, in Xenopus embryos, microtubules form bundles along cell cortices perpendicular to the wound edge (Figure 1C) (Shindo et al , 2018). Disrupting microtubules results in reduced elongation of the cells adjacent to the wound edge, suggesting that microtubule bundles may stabilize the lateral edges of cells as they elongate into the wounded region (Shindo et al , 2018).…”

“…In addition, in Xenopus embryos, microtubules form bundles along cell cortices perpendicular to the wound edge (Figure 1C) (Shindo et al , 2018). Disrupting microtubules results in reduced elongation of the cells adjacent to the wound edge, suggesting that microtubule bundles may stabilize the lateral edges of cells as they elongate into the wounded region (Shindo et al , 2018).…”

“…Septins can interact with both actin filaments and microtubules, as well as the cell membrane. Notably, Sept7, which is a subunit of septin heterooligomers, localizes to the lateral cell edges and to the wound edge in Xenopus embryos (Figure 1D) (Shindo et al , 2018). Sept7 is required for the reorientation and organization of microtubules during wound closure, as well as for contraction of the actomyosin cable around the wound (Shindo et al , 2018), suggesting that septins may coordinate the rearrangements of different cytoskeletal networks during embryonic wound repair (Figure 3, magenta).…”