Fig. 4. gbb is expressed in the somatic cells of the germarium and is essential for maintaining GSCs and for repressing bam transcription in GSCs. (A) A DNA gel with RT-PCR products showing that gbb is expressed in the somatic cells of the germarium but not in GSCs. In this gel, mRNA for whole ovaries, agametic ovaries, inner sheath cells and GSC-like germ cells are marked by templates 1, 2, 3 and 4, respectively. vasa and dpp genes are positive controls, whereas rp49 is an internal control. Germaria in B-E are labeled for Hts (red, fusomes) and DAPI (blue), whereas germaria in F-I are labeled for Hts (red, fusomes), GFP (green) and DAPI (blue). Circles highlight cap cells, whereas asterisks indicate GSCs. (B) Germarial tip from a wild-type bam-GFP female cultured at 29°C for 1 week showing two GSCs. (C-E) Germarial tips from the bam-GFP gbb⁴/gbb^D4 females cultured at 29°C for one week showing one GSC (C), no GSC but 16-cell cysts (one indicated by arrow; D) and no GSCs and no cysts (E). (F) Germarial tip from a bam-GFP gbb⁴/gbb^D4 female cultured at room temperature for 2 days showing that the remaining GSC does not express bam. (G,H) Germarial tips from bam-GFP gbb⁴/gbb^D4 (G) and bam-GFP gbb⁴/gbb^D20 (H) females cultured at 29°C for one week, showing that the remaining single GSC expresses bam. (I) A germarial tip from a c587-gal4/UAS-gbb; bam-GFP female showing a normal number of GSCs, and normal bam-GFP expression in cystoblasts (arrow) and other differentiated germ cells. Scale bar in B: 10 µm for B-I.