Fig. 4: Ectopic Pvr activation is sufficient to activate ISCs and accelerate tissue turnover.

a–c Confocal images of guts expressing E-Cad::GFP under its endogenous promoter to label cell-cell adhesion junctions (in green) and ISC^ts-driven expression of LifeAct (to label F-actin in red) alone (a–a”’, control) or with ISC-specific Pvr activation (b–b”’, ISC^ts>Pvr^CA). Ectopic Pvr activation results in large-flattened ISCs that form actin-based protrusions in a non-coordinated fashion, quantified as an increase in cell size in (c, n = 13/333, 11/139 guts/cells). (d–f) The effect of ISC-specific Pvr activation on Rac1 activity was followed using a Rac1 sensor (pak3^RBD::GFP). Confocal images of posterior midguts from control flies d and flies with ISC-specific Pvr^act expression e showing an increase in Rac activity levels upon activation of Pvr in ISCs as quantified in (f) (n = 16, 15 guts). g–j The large-flattened morphology and formation of actin-based protrusions triggered by ISC-specific Pvr activation (h compared to g) are suppressed upon knockdown of Rac (i). Confocal images of dissected posterior midguts from uninfected (k, control) and P.e. infected control flies (l) and flies with ISC-specific Pvr knockdown m showing that the increase in Rac activity associated with oral P.e. infection (l compared to k) is suppressed upon Pvr knockdown m as quantified in (n) (n = 9/68, 15/124, 15/100 guts/ROI). o–q The TransTimer system was used to follow the differentiation of ISCs into progenitors (EBs) and mature EECs and ECs in control guts (o–o”) and guts with ISC-specific Pvr activation (p–p”). Confocal images of posterior midguts from control flies (o–o”) and flies expressing Pvr^act (p–p”) in ISCs using ISC^TransTimer tracing for 2 days. Pvr activation results in accelerated tissue turnover visualized by an increase in the number of EBs and mature EECs and ECs (red only cells, p–p”) compared with control guts (o–o”) as quantified in (q) (n = 22, 25 guts). Significance was tested with a two-tailed Mann–Whitney test (c, f,q) or Kruskal–Wallis with post-hoc multiple comparison analysis (n). Data are presented as mean values ± SD or ± SEM (c, n). Source data are provided as a Source data file.