Tkv prevents ectopic Dpp signaling. (A) A WT germarium contains two pMad-positive GSCs within the niche. (B) A control (Dad-lacZ/+) germarium contains five Dad-lacZ–positive cells. (C) A tkvⁱ (Bl-40937) germarium exhibits more pMad-positive spectrosome-containing cells. (D) A germarium carrying tkv⁸ ECs (arrowheads) also contains more pMad-positive cells. Genotype: c587.UAS-flp; FRT40A.ubiGFP/FRT40A.tkv⁸. (E) Relative pMad intensity in ectopic spectrosome-containing cells in germaria carrying tkv⁸ ECs (n = 113) compared with GSCs (n = 10). (F) A tkvⁱ (Bl-40937) germarium exhibits ectopic Dad-lacZ–positive spectrosome-containing cells. (G and H) dpp mRNA is strongly detected in the cap cells of WT (G) or tkvⁱ (H; v3059) germarium. (I and J) knockdown of Dpp in the ECs of a tkvⁱ (v3059) germarium does not suppress the formation of more spectrosome-containing cells. (K–M) Knockdown of Dpp in cap cells causes germ cell loss in a tkvⁱ (BL-40937) germarium. (N) Statistical data for I–M. (O) Knocking down Tkv in germline cells in a tkvⁱ (BL-40937) germarium results in the loss of germ cells. (P) A germarium without cap cell–contacting tkv⁸ mutant ECs does not exhibit more spectrosome-containing cells. tkv⁸ mutant clones are indicated by arrowheads. Genotype: c587.UAS-flp; FRT40A.ubiGFP/FRT40A.tkv⁸. (P′) Cartoon model to illustrate the positions of non cap cell–contacting EC mutant clones (blue). Error bars represent the SEM. ***, P < 0.001. Bars, 10 µm.