Epithelial apoptotic pattern emerges from global and local regulation by cell apical area

Epithelial apoptosis: A back-and-forth mechanical interplay between the dying cell and its surroundings

Apoptosis is an essential cellular process corresponding to a programmed cell suicide. It has long been considered as a cell-autonomous process, supposed to have no particular impact on the surrounding tissue. However, it has become clear in the last 15 years that epithelial apoptotic cells interact mechanically and biochemically with their environment. Here, we explore recent literature on apoptotic mechanics from an individual dying cell to the back-and-forth interplay with the neighboring epithelial tissue. Finally, we discuss how caspases, key regulators of apoptosis, appear to have a dual function as a cytoskeleton regulator favoring either cytoskeleton degradation or dynamics independently of their apoptotic or non-apoptotic role.

Piezo regulates epithelial topology and promotes precision in organ size control

Mechanosensitive Piezo channels regulate cell division, cell extrusion, and cell death. However, systems-level functions of Piezo in regulating organogenesis remain poorly understood. Here, we demonstrate that Piezo controls epithelial cell topology to ensure precise organ growth by integrating live-imaging experiments with pharmacological and genetic perturbations and computational modeling. Notably, the knockout or knockdown of Piezo increases bilateral asymmetry in wing size. Piezo's multifaceted functions can be deconstructed as either autonomous or non-autonomous based on a comparison between tissue-compartment-level perturbations or between genetic perturbation populations at the whole-tissue level. A computational model that posits cell proliferation and apoptosis regulation through modulation of the cutoff tension required for Piezo channel activation explains key cell and tissue phenotypes arising from perturbations of Piezo expression levels. Our findings demonstrate that Piezo promotes robustness in regulating epithelial topology and is necessary for precise organ size control.

The G1/S transition in mammalian stem cells in vivo is autonomously regulated by cell size

Cell growth and division must be coordinated to maintain a stable cell size, but how this coordination is implemented in multicellular tissues remains unclear. In unicellular eukaryotes, autonomous cell size control mechanisms couple cell growth and division with little extracellular input. However, in multicellular tissues we do not know if autonomous cell size control mechanisms operate the same way or whether cell growth and cell cycle progression are separately controlled by cell-extrinsic signals. Here, we address this question by tracking single epidermal stem cells growing in adult mice. We find that a cell-autonomous size control mechanism, dependent on the RB pathway, sets the timing of S phase entry based on the cell's current size. Cell-extrinsic variations in the cellular microenvironment affect cell growth rates but not this autonomous coupling. Our work reassesses long-standing models of cell cycle regulation within complex metazoan tissues and identifies cell-autonomous size control as a critical mechanism regulating cell divisions in vivo and thereby a major contributor to stem cell heterogeneity.

Applying mechanical forces on Drosophila tissues in vivo using the StretchCo, a 3D-printable device

Applying mechanical forces to tissues helps to understand morphogenesis and homeostasis. Additionally, recording the dynamics of living tissues under mechanical constraints is needed to explore tissue biomechanics. Here, we present a protocol to 3D-print a StretchCo device and use it to apply uniaxial mechanical stress on the Drosophila pupal dorsal thorax epithelium. We describe steps for 3D printing, polydimethylsiloxane (PDMS) strip cutting, and glue preparation. We detail procedures for PDMS strip mounting, tissue compaction, and live imaging upon force application. For additional details on the use and execution of this protocol, please refer to Cachoux et al. (2023)1 from which the StretchCo machine has been derived.

Epithelial homeostasis: Cell size shapes cell fate

A new study shows that cell size, in conjunction with specific signaling pathways, controls apoptosis within developing tissues. Cells with smaller sizes and relatively smaller sizes compared to their neighbors exhibit an increased likelihood of undergoing apoptosis. These processes are regulated by the Hippo/YAP and Notch pathways, respectively.