A unicellular relative of animals generates a layer of polarized cells by actomyosin-dependent cellularization

Dudin, O., Ondracka, A., Grau-Bové, X., Haraldsen, A. A. B., Toyoda, A., Suga, H., Bråte, J. and Ruiz-Trillo, I. 2019. eLife. doi:10.7554/eLife.49801

Figure 1. Cellularization dynamics in Sphaeroforma arctica Figure 2. Actin cytoskeleton and plasma membrane dynamics during cellularization of S. arctica Figure 3. Transcriptional dynamics across the S. arctica life cycle Figure 4. Dynamics of lincRNAs, alternative splicing, and gene phylostrata Figure 5. Temporal transcript abundance of cytoskeletal, cell polarity and cell adhesion genes Figure 6. The actomyosin network organization is crucial for cellularization of S. arctica


In animals, cellularization of a coenocyte is a specialized form of cytokinesis that results in the formation of a polarized epithelium during early embryonic development. It is characterized by coordinated assembly of an actomyosin network, which drives inward membrane invaginations. However, whether coordinated cellularization driven by membrane invagination exists outside animals is not known. To that end, we investigate cellularization in the ichthyosporean Sphaeroforma arctica, a close unicellular relative of animals. We show that the process of cellularization involves coordinated inward plasma membrane invaginations dependent on an actomyosin network and reveal the temporal order of its assembly. This leads to the formation of a polarized layer of cells resembling an epithelium. We show that this stage is associated with tightly regulated transcriptional activation of genes involved in cell adhesion. Hereby we demonstrate the presence of a self-organized, clonally-generated, polarized layer of cells in a unicellular relative of animals.