Mitotic cell rounding and epithelial thinning regulate lumen growth and shape

Abstract

Many organ functions rely on epithelial cavities with particular shapes. Morphogenetic anomalies in these cavities lead to kidney, brain or inner ear diseases. Despite their relevance, the mechanisms regulating lumen dimensions are poorly understood. Here, we perform live imaging of zebrafish inner ear development and quantitatively analyse the dynamics of lumen growth in 3D. Using genetic, chemical and mechanical interferences, we identify two new morphogenetic mechanisms underlying anisotropic lumen growth. The first mechanism involves thinning of the epithelium as the cells change their shape and lose fluids in concert with expansion of the cavity, suggesting an intra-organ fluid redistribution process. In the second mechanism, revealed by laser microsurgery experiments, mitotic rounding cells apicobasally contract the epithelium and mechanically contribute to expansion of the lumen. Since these mechanisms are axis specific, they not only regulate lumen growth but also the shape of the cavity.

Mechanical control of mitotic progression in single animal cells

“…Indeed, although strategies for chemical perturbation of cell division have been pursued for decades (36), the advent of mechanical approaches opens the door to studies of physical perturbation. Our approach expands the applicability of in vitro cell mechanics studies by providing a platform to understand how confinement forces can affect mitosis (8). Further studies could lead to novel concepts, for example, perturbing cell division with a combination of cortex-weakening agents and external force (37).…”

“…I n mitosis, eukaryotic cells down-regulate focal adhesions and increase their cortical tension and intracellular pressure, thereby generating force to round up against external impediments (1)(2)(3). Recent studies in the epithelium and epidermis of various organisms indicate that mitotic cell rounding is involved in tissue organization, development, and homeostasis (4)(5)(6)(7)(8). Abnormal mitotic cell shape can have adverse consequences for chromosome segregation and tissue growth (9), in some cases contributing to tumorigenesis (7).…”

Cavity morphogenesis: imaging mitotic forces in action

“…While this is also happening in the inner ear, we found that every epithelial cell also reduces its volume and changes its shape, thinning the epithelium. 4 This would result in a net redistribution of fluid from the cells to the lumen, a novel kind of fluid flow. This seems to be a general feature of lumen formation processes, as tissue thinning during lumen growth can be observed in many lumen-forming organs.…”

“…The understanding of these shaping mechanisms in vivo is challenging, as most of these organs are large and located deep in the embryo, hindering their in vivo imaging and whole 3D lumen reconstruction. We recently tackled this issue by imaging in real time the dynamics of lumenogenesis in the zebrafish inner ear, 4 a small and rather superficially located organ. Not studied before, the zebrafish otic vesicle lumen displays an asymmetric shape that resembles a biaxial ellipsoid, with one long axis and 2 equally sized short axes ( Fig.…”

“…This seems to be a general feature of lumen formation processes, as tissue thinning during lumen growth can be observed in many lumen-forming organs. 4 Finally, as both the tissue thinning and contraction are not occurring in a uniform manner over the entire vesicle, they constitute direct shaping mechanisms. 4 While the thinning occurs preferentially along the short axes, the contraction occurs close to the long axis poles.…”