Fig. 2

Rbfox1 is a pro-survival factor that regulates follicular epithelium differentiation. a In starved females, Rbfox1-overexpressing clones (Rbfox1 OE, GPF-positive, hsFlp; UAS-Rbfox1-RE/ + ; act > CD2 > Gal4 UAS-GFP) have higher cell density and decreased cell death. Note condensed DNA (separate channel, arrows) in non-clonal control cells, which die in response to starvation. b Abnormal autophagy measured by the significantly increased Atg8 intensity in Rbfox1 OE (n = 27) versus neighbouring control cells within the same egg chamber (n = 27); c Decreased apoptosis in Rbfox1 OE cells detected by the reduced Caspase3 intensity (Rbfox1 OE, n = 28, Control, n = 35). d Even without starvation, Rbfox1 overexpression reduces cell growth, illustrated by the significantly decreased Myc expression in Rbfox1 OE clones in comparison to the equal size of the non-clonal neighboring area within the same egg chamber (n = 17). e Rbfox1 OE cells express higher levels of the cell adhesion proteins Cadherin (DE-Cad, n = 10 clones) and β-Catenin (Arm, n = 5 clones), and form a multilayered epithelium (arrow, f). g, h Temporal regulation of the Notch-dependent transcription factor Cut is abnormal, showing that activation of Notch signaling required for proper follicle cell differentiation is slowed-down upon Rbfox1 overexpression (g). i When Rbfox1 is downregulated, Cut expression is also abnormal. h Bar graph and scheme show that timely repression or activation of Cut is delayed in the endocycling (st.6-10a) or amplifying (st.10b-14) mutant follicular epithelial cells, respectively. Cut expression during endocycling stages was detected in 20% and 80% of clones that have higher or lower Rbfox1 levels, respectively, in comparison to 0% in control non-clonal cells. At the same time, significantly higher percentages, 80% and 70% of clonal cells with overexpressed or downregulated Rbfox1, failed to turn on Cut expression during amplification stages (n = 19 and 43 clones for Rbfox1 OE and Rbfox1 KD, respectively). j Scheme represents miR-980/Rbfox1 function in response to nutritional stress. Upon stress, miR-980 levels are reduced, causing Rbfox1 upregulation and promoting cell survival. Images in a–g and i are maximum intensity projections of multiple Z-sections. Scale bars 5 µm. Developmental stages (st.) of egg chambers are marked. Relative antibody staining intensity (AVE ± AD) is presented as relative to control (b–e). Student’s t-test was applied for statistics in b–e and Chi square in h, *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001