Fig. 4: Follicle cell expansion behavior bridges epithelial cell flattening and elongation to oocyte growth and extension.

a Representative cross-section images of E-cadherin-GFP labeled egg chambers during the cell expansion behavior, showing follicle cell flattening process. Dotted boxes show the enlarged images (below). b Quantification of flatten ratio of follicle cells. c The correlation assay of follicle cell basal area and oocyte area in egg chambers during the spreading phase. One-sided simple linear regression, p <  0.0001, R²  =  0.7751, n = 20 independent cells and oocytes. d, e Boundary outline marks temporal changes (RGB color bars) of one representative follicle cell (d) and oocyte (e) during the spreading phase. Since follicle cell boundary outlines from 0 to 100 min blocked us to view cell shape during the spreading process, boundary outlines at 0 and 100 min have been shown separately to highlight follicle cell elongation status. f Quantification of A–P length/D–V length ratio of follicle cells and oocytes. g Quantification of dynamic changes of the height in one representative indicated follicle cell after the ruffling phase. n  =  10 independent cells and data are presented as mean values ± SD. h Quantification of oocyte area increase from the indicated follicular epithelia during the increasing phase. i Quantification of A–P length/D–V length ratio in the indicated follicle cells during the spreading phase. j Boundary outlines mark temporal changes (color bars) of one representative oocyte from WT, Rac1DN-expressing, Rho1DN-expressing, Paxillin-expressing, or Talin RNAi-expressing follicular epithelium during the spreading phase. k Quantifications of A–P length/D–V length ratio of the oocytes from the indicated follicular epithelia during the spreading phase. l Representative cartoons to summarize follicle cell expansion waves correlated with follicle cell flattening and A–P elongation as well as oocyte growth and A–P elongation. Green and red colors mark E-cadherin and stress fibers, respectively. Scale bars are 10 μm in (a). The middle line shows medians, upper and lower lines as 25th and 75th percentiles, each datapoint is displayed as a dot, in (b, f, h, i, k). All P values have been listed in Supplementary Note 1. Source data are provided as a Source Data file.