Figure 1

Introduction to the mitotic shift. (A) The Drosophila wing imaginal disc. Neuroglian-GFP (green) marks the septate junctions. (B) The Drosophila wing disc epithelium. The rounded cell (center) is undergoing mitosis. (C) The mitotic shift in Drosophila (red) and Cucumis (green) [9, 24]. The overall distribution of cellular shapes has a hexagonal mean (red and green). By contrast, the mitotic cell shape distribution (red and green) is shifted to have a heptagonal mean in both organisms. Hence, one distribution is approximately a shifted version of the other. Sample sizes for both organisms are given under the heading “Sample sizes for overall and mitotic cell shape distributions” in the Methods section. (D) Representative mitotic cells (as detected based on cell rounding) in the Drosophila wing imaginal disc. Mitotic cells show an enrichment in cell-cell contacts. Stars (black) mark neighboring cells; labeled cells’ polygonal topologies are designated in black. (E-F) An overview of mitotically induced topological transformations during epithelial proliferation. (E) An illustration of autonomous “side loss” during polygonal cell division. The octagonal cell (green) gives rise to two hexagonal daughters (grey). On average, a mitotic N-sided cell will give rise to daughters having (N + 4)/2 sides, making side loss a general trend except for rare polygonal cells in which N = 3 or N = 4. Note the creation of a set of new tri-cellular junctions (red), which are formed at either end of the cleavage plane (black), which is depicted as a dashed line. (F) Non-autonomous “side gaining” due to neighbor cell mitoses. In this example, a pentagonal cell (blue), gains one neighbor to become a hexagonal cell (grey). In general, during polygonal cell division, exactly two neighboring cells adjacent to the newly-formed tri-cellular junctions (red) will effectively gain one neighbor each.