Tissue-specific knockdown of dicer-1 by tissue-specific expression of dicer-1 RNAi. (A) Functional segregation of Drosophila dicer-1 (required for microRNA synthesis) and dicer-2 (required for RNAi) theoretically allows knockdown of dicer-1 protein by dicer-1 RNAi. (B) Images show a portion of a single ventral body wall hemisegment in a third instar Drosophila larva. Ventral longitudinal muscles 6 and 7 (VLM 6 and VLM 7) are labeled, as are the presynaptic motor terminals (stained with anti-HRP; magenta) that innervate these muscles. In control muscles (24Bgal4/+), dicer-1 immunoreactivity (green) appears most prominently as puncta scattered throughout the muscle, but also as a faint cytoplasmic haze. In animals expressing dicer-1 RNAi in muscle cells (24BGal4/UAS-dcr1.RNAi), the intensity of the dicer-1 immunoreactive haze and the number of dicer-1 puncta are significantly reduced, which is consistent with a large reduction in dicer-1 in these cells. The differences in dicer-1 immunoreactive puncta density and overall immunofluorescence are quantified and statistically compared in C and D (n = 6–7 for each genotype). Error bars represent SEM. *, P < 0.01; ***, P < 0.0001.