Growth compensation upon changes in tissue size in the Drosophila abdomen

Attaining the appropriate size during development is essential for the function of animal tissues and organs. Robust tissue size control implies the existence of compensatory mechanisms that allow developing systems to recover from growth perturbations. However, the difficulty of directly observing normal or compensatory developmental growth means we have little understanding of the cellular behaviours that confer robustness to tissue size control. Here, we study how growth perturbations affect proliferation kinetics and the timing of growth termination of Drosophila histoblasts, the progenitors that give rise to the adult abdominal epidermis. Histoblasts undergo extensive growth and proliferation during the pupal stage, which is accessible for long-term live-imaging and precise quantitative analysis. By manipulating cell number or volume prior to the pupal growth phase, we changed the starting size of the abdomen primordium, then observed how the histoblasts adapted to these changes by altering their growth dynamics. We show that, upon a decrease in starting tissue size, the histoblasts compensate by extending their temporal proliferative window, undergoing additional cell cycles, as well as increasing their apical area to maximise coverage of the abdominal surface. When initial tissue size is increased, the histoblasts undergo fewer division cycles and arrest proliferation earlier than normal. Thus, the proliferative window of this tissue is flexible enough to buffer for changes in tissue size. Our data also suggest that the histoblasts sense both spatial and temporal cues to arrest their growth at the appropriate time and ensure accurate tissue size control.