Balachandra, S. | Search bioRxiv

bioRxiv2018

Long-term live imaging of the Drosophila adult midgut reveals real-time dynamics of cell division, differentiation, and loss

Organ renewal is governed by the dynamics of cell division, differentiation, and loss. To study these dynamics in real time, here we present a platform for extended live imaging of the adult Drosophila midgut, a premier genetic model for stem cell-based organs. A window cut into a living animal allows the midgut to be imaged while intact and physiologically functioning. This approach prolongs imaging sessions to 12-16 hours and yields movies that document cell and tissue dynamics at vivid spatiotemporal resolution. Applying a pipeline for movie processing and analysis, we uncover new, intriguing cell behaviors: that mitotic stem cells dynamically re-orient, that daughter cells delay fate-determining Notch activation for many hours after birth, and that enterocytes extrude via constriction of a pulsatile cadherin ring. By enabling real-time study of cellular phenomena that were previously inaccessible, our platform opens a new realm for dynamic understanding of midgut organ renewal.

cell biology↗

bioRxiv2017

Feedback regulation of steady-state epithelial turnover and organ size

Epithelial organs undergo steady-state turnover throughout adult life, with old cells being continually replaced by the progeny of stem cell divisions1. To avoid hyperplasia or atrophy, organ turnover demands strict equilibration of cell production and loss2-4. However, the mechanistic basis of this equilibrium is unknown. Using the adult Drosophila intestine5, we find that robustly precise turnover arises through a coupling mechanism in which enterocyte apoptosis breaks feedback inhibition of stem cell divisions. Healthy enterocytes inhibit stem cell division through E-cadherin, which prevents secretion of mitogenic EGFs by repressing transcription of the EGF maturation factor rhomboid. Individual apoptotic enterocytes promote divisions by loss of E-cadherin, which releases cadherin-associated {beta}-catenin/Armadillo and p120-catenin to induce rhomboid. Induction of rhomboid in the dying enterocyte triggers EGFR activation in stem cells within a discrete radius. When we block apoptosis, E-cadherin-controlled feedback suppresses divisions, and the organ retains the same number of cells. When we disrupt feedback, apoptosis and divisions are uncoupled, and the organ develops either hyperplasia or atrophy. Altogether, our work demonstrates that robust cellular balance hinges on the obligate coupling of divisions to apoptosis, which limits the proliferative potential of a stem cell to the precise time and place that a replacement cell is needed. In this manner, localized cell-cell communication gives rise to tissue-level homeostatic equilibrium and constant organ size.

developmental biology↗