Fig. 6.
αPS1βPS and αPS2βPS have distinct functions for follicle-cell stress-fibre organization. (A,B) In situ hybridization on whole egg chambers showing in black the levels of mRNAs encoding αPS1 (A) and αPS2 (B) during oogenesis. (C-D′) Clones of cells lacking αPS1, marked by the absence of GFP. (C,D) Position of the mutant cells (not green) are shown together with the distribution of actin (red) and another protein if relevant (blue). (C,C′) Cells lacking αPS1 form fibres with brighter actin intensity than in wild-type cells; compare arrowheads. (D,D′) Loss of αPS1 elevates αPS2 levels; compare arrowheads. (E-E″) Overexpression of αPS2 using the UAS-GAL4 system increased αPS2 levels (E″) but did not change the actin fibres (E′). (F-G′) Clones of cells lacking αPS2, marked by the presence of GFP (MARCM clones of ifB4). (F,F′) Loss of αPS2 does not perturb stress fibres; compare arrowheads pointing to a wild-type and a mutant cell on F′. (G-G′) αPS1 level in focal adhesions was increased when αPS2 was removed; compare arrowheads in G′. (H) Quantification of basal F-actin in cells lacking αPS1 (mew) compared to wild type (WT) as shown in C and measured as integrated area (grey mean value multiplied by the cell area). Wild-type value (106) divided by mutant value (147) is 0.72, which indicates a rough increase of 38% in basal actin in the mutant cells, comparable to the increase observed in the total absence of integrins (see Fig. 2E). P=1.5.E-8 (Student's t-test two samples assuming equal variances). (I-I′″) Re-expression of αPS1 (blue, I′″) in cells lacking αPS2 (CD8-GFP, green, I″) and stained for actin (red, I′) and αPS2 (green also, I″) results in a delay in stress-fibre re-orientation at stage 12 (I′); most stress fibres in CD8-GFP-positive cells have failed to reorient compared to WT neighbours. (J-J″,L) Global (J) and magnified (J′) view of the basal surface of an egg chamber at early stage 12 where the whole follicular epithelium lacks αPS2 and re-expresses αPS1. In this extreme case, the stress fibres have random orientation yet the whole egg morphology is normal (J″) compared to a wild-type egg chamber (K). Scale bar in B: 50 μm (for A,B,J″,K); scale bar in F: 20 μm (for C-I′″); scale bars in J and J′: 20 μm.