Ventral enclosure (VE) is a key part of epidermal morphogenesis, where the ventral surface of the C. elegans embryo is enclosed in a layer of epithelial cells. VE requires the coordinated migration of ventral epidermal cells and their adhesion at the ventral midline. Known regulators of VE include RhoGTPases, nucleators of F-actin and the catenin/cadherin complex. There likely are additional proteins that regulate F-actin for cell shape change, migration and/or adhesion that have not yet been identified. One candidate is anillin, ANI-1, a multi-domain scaffolding protein that coordinates actomyosin contractility in the early embryo. We show that
ani-1 is required for epidermal morphogenesis. In
ani-1 RNAi embryos expressing AJM-1:GFP (adherens junctions marker), ventral epidermal cells fail to meet and adhere at the ventral midline. Although they migrate at a rate comparable to control embryos, they often are not properly aligned with their contralateral neighbors. Interestingly, ANI-1 does not localize to adherens junctions or epidermal F-actin, but is present in HAM-1-expressing neuroblasts. Neuroblasts lie underneath the epidermis and are hypothesized to serve as a substrate for ventral epidermal cell migration, likely by providing chemical cues for their guidance. ANI-1 localizes to the cleavage furrows of dividing neuroblasts, which fail to divide upon ANI-1 depletion, suggesting that ANI-1 regulates neuroblast cytokinesis. In support of ANI-1's non-autonomous regulation of VE,
ani-1 RNAi enhances VE phenotypes caused by hypomorphic alleles of the catenin/cadherin complex. Also, ANI-1 and alpha-catenin co-suppress one another when one is over-expressed and the other is mutated or depleted by RNAi. Therefore, strengthening the junctions between cells (e.g. by alpha-catenin over-expression) could make the substrate partially redundant and likewise, strengthening the cytoskeleton of the substrate (e.g. by ANI-1 over-expression) could make junctions partially redundant. These data support the model that mechanotransduction between multiple tissues in the developing embryo is essential for epidermal morphogenesis.