Mechanical Forces Program the Orientation of Cell Division during Airway Tube Morphogenesis

Abstract

Oriented cell division plays a key role in controlling organogenesis. The mechanisms for regulating division orientation at the whole-organ level are only starting to become understood. By combining 3D time-lapse imaging, mouse genetics, and mathematical modeling, we find that global orientation of cell division is the result of a combination of two types of spindles with distinct spindle dynamic behaviors in the developing airway epithelium. Fixed spindles follow the classic long-axis rule and establish their division orientation before metaphase. In contrast, rotating spindles do not strictly follow the long-axis rule and determine their division orientation during metaphase. By using both a cell-based mechanical model and stretching-lung-explant experiments, we showed that mechanical force can function as a regulatory signal in maintaining the stable ratio between fixed spindles and rotating spindles. Our findings demonstrate that mechanical forces, cell geometry, and oriented cell division function together in a highly coordinated manner to ensure normal airway tube morphogenesis.

Cell-based Simulations of Biased Epithelial Lung Growth

“…We have used our cell-based tissue simulation framework LBIBCell to explore how biased epithelial outgrowth is achieved during mouse lung development. Experimental studies have previously linked the observed bias in outgrowth to a bias in cell shapes and cell division [4,5], and the simulations demonstrate that this is indeed plausible as long as the cortical tension is sufficiently high. The requirement for high cortical tension is consistent with the observation that biased outgrowth is lost in mutants that express a constitutive active form of KRas (Shh cre/+ ; KRas LSL/+ ) [4].…”

“…We sought to analyze whether the observed bias in cell shape and cell division orientation ( Figure 3a-c) would be sufficient to explain the measured bias in embryonic lung tube outgrowth [4,5]. To this end, we simulated tissue growth using parameter values that are consistent with measurements in mouse lung epithelia (Table 1), and we divided cells either according to the biased mitotic spindle angle distribution that has been experimentally measured in wildtype mouse lungs (Figure 3b) or according to the uniform mitotic spindle angle distribution of Shh cre/+ ; Kras LSL/+ mutant ( Figure 3c) mouse lung epithelia [4].…”

“…the circumference widens to the same extent as the tube elongates [3], whereas the mouse embryonic lung bronchi show biased outgrowth, i.e. the epithelial tube lengthens more than it widens [4,5]. The biased outgrowth of embryonic mouse lung bronchi has been related to a bias in the orientation of the mitotic spindles of the dividing cells: ∼ 42% of the dividing cells orient their mitotic spindle in the direction of elongation [4].…”

“…According to Hertwig's rule, cells divide through their mass point, and perpendicular to their longest axis ( Figure 1e) [7,8]. Indeed, the bias in cell division is accompanied by a bias in cell shape [5]. But how does the bias in cell shape arise in the embryonic lung?…”

“…Cell-based simulations are particularly useful when quantitative data is available to inform cell-based rather than continuous models [34,30]. In case of epithelia, quantifications of the apical polygonal lattice are available for a wide range of epithelia from Drosophila and mouse [4,35,36,5,37]. These can be used to adjust the mechanical parameters in the model [37,38].…”