Figure 3.

Autonomous Activin signaling disrupts hub cell quiescence

(A) Expression of Babo-GFP fusion protein (green, single channel in A′) is detected in the testis apex. In particular, Babo-GFP expression is visible in hub cells (labeled with Fas3, red), outlined with a red dashed line in (A′). Vasa (blue) labels the germline.

(B) Graph showing the number of hub cells in control testes (upd^TS>+, gray bars, n = 23 for 0 days, n = 15 for 1 week, n = 13 for 2 weeks, n = 8 for 3 weeks, n = 84 for 4 weeks) or those with sustained Activin signaling in hub cells (upd^TS>babo^QD, purple bars, n = 16 for 0 days, n = 16 for 1 week, n = 28 for 2 weeks, n = 35 for 3 weeks, n = 30 for 4 weeks) at the indicated time points. Note the progressive loss of hub cells in upd^TS>babo^QD.

(C) Confocal sections of upd^TS>babo^QD testes at the indicated time points. Fas3 (green) marks hub cells and TO-PRO (magenta) marks DNA.

(D and E) Lineage tracing hub cells in control upd^TS>+ (D) and upd^TS>babo^QD testes (E). Note in (E) the presence of hub-lineage-positive (green) cells outside of the niche that express the CySC marker Zfh1 (red). Fas3 (blue) marks hub cells and TO-PRO (DNA) is white. In (E′), yellow and red arrowheads indicate hub-lineage-positive CySCs and hub-lineage-negative CySCs, respectively, and the green arrowheads indicate differentiating cyst cells descended from a hub-lineage CySC. Blue lines in (C and D) indicate Fas3-positive hub cells.

(F) Graph indicating the percentage of CySCs positive for hub lineage in upd^TS>+ (gray bar, n = 34) and upd^TS>babo^QD (purple bar, n = 26) testes.

Error bars represent the data range. ^∗∗∗∗p < 0.0001; ^∗∗∗p < 0.001. ns, not significant as assessed by Student’s t test.

See also Tables S1 and S2.

Scale bar, 5 μM in (C) and 10 μM in all other panels.