Apical Constriction Reversal upon Mitotic Entry Underlies Different Morphogenetic Outcomes of Cell Division

Abstract

1During development, coordinated cell shape changes and cell divisions sculpt 2 tissues. While these individual cell behaviors have been extensively studied, how cell 3 shape changes and cell divisions that occur concurrently in epithelia influence tissue 4 shape is less understood. We addressed this question in two contexts of the early 5Drosophila embryo: premature cell division during mesoderm invagination, and native 6 ectodermal cell divisions with ectopic activation of apical contractility. Using quantitative 7 live-cell imaging, we demonstrated that mitotic entry reverses apical contractility by 8 interfering with medioapical RhoA signaling. While premature mitotic entry inhibits 9 mesoderm invagination, which relies on apical constriction, mitotic entry in an artificially 10 contractile ectoderm induced ectopic tissue invaginations. Ectopic invaginations 11 resulted from medioapical myosin loss in neighboring mitotic cells. This myosin loss 12 enabled non-mitotic cells to apically constrict through mitotic cell stretching. Thus, the 13 spatial pattern of mitotic entry can differentially regulate tissue shape through signal 14 interference between apical contractility and mitosis. 15To determine whether loss of medioapical myosin was a general feature of 131 dividing, contractile epithelial cells, we took advantage of the stereotyped cell divisions 132 in the early mitotic domains that occur on the dorsal side of the head (Foe, 1989), 133 particularly focusing on mitotic domains 1 and 5 ( Figure 2C). We artificially increased 134 ectoderm apical contractility by ectopically expressing folded gastrulation (fog), a ligand 135 for a G-protein-coupled receptor (GPCR) that is expressed in the mesoderm and 136 functions upstream of apical myosin activation (Costa et al., 1994; Dawes-Hoang et al., 137 ,-.

The nature of cell division forces in epithelial monolayers

“…While it has been known that cells have the ability to generate large forces during cell spreading through the formation of robust adhesions and polymerization of branched actin networks, our work ties these forces to enabling reintegration of daughter cells into the monolayer. Beyond their role in driving division, division forces have been linked to tissue-scale biological processes, such as collective cell migration observed in intestinal crypts and villi (Parker et al, 2017;Krndija et al, 2019), cell rearrangements within chick embryos (Firmino et al, 2016), invagination within developing Drosophila embryos (Kondo and Hayashi, 2013;Ko et al, 2020), apical invagination during intestine villi formation (Freddo et al, 2016), and lumen growth (Hoijman et al, 2015). While previous work has typically attributed division forces to mitotic rounding, these processes are inherently anisotropic.…”

Actin-based force generation and cell adhesion in tissue morphogenesis

“…During C. elegans gastrulation, cell ingression is assisted by neighboring cells pushing with Arp2/3-mediated actin protrusions 90 . Entry of cells into mitosis has also been shown to be associated with apical relaxation, which can promote apical constriction and invagination of neighboring contractile cells 37,91 . Thus, understanding morphogenetic events requires investigating both the local properties of the tissue undergoing shape change, as well as the properties of the surrounding environment because both can contribute to movement.…”

The nature of mitotic forces in epithelial monolayers

“…While it has been known that cells have the ability to generate large forces during cell spreading, through the formation of robust adhesions and polymerization of branched actin networks, our work ties these forces to enabling reintegration of daughter cells into the monolayer. Beyond their role in mitosis, mitotic forces have been linked to tissue-scale biological processes such as collective cell migration observed in intestinal crypts and villi 2,5 , cell rearrangements within chick embryos 4 , and invagination within developing Drosophila embryos 7,35 . While previous work has typically attributed mitotic forces to mitotic rounding, these processes are inherently anisotropic.…”