FIGURE 1:

Nipped-A is required in the germ line for differentiation of the germline stem cell daughter. (A) Schematic representation of a Drosophila germarium where germ cells (blue) are surrounded by somatic cells (gray). The germline stem cells (GSCs) reside in the germarium and are maintained by a somatic niche. The GSC divides to give rise to a daughter, called a precystoblast (pre-CB). The pre-CB turns on differentiation factors and is then called the cystoblast (CB). The CB undergoes incomplete mitotic divisions to give rise to 2-, 4-, 8-, and 16-cell cysts. Single cells are marked by punctate structures called spectrosomes (red), and cysts are marked by the elongated, branched spectrosomes called fusomes (red). The 16-cell cyst migrates, buds off from the germarium, and is encapsulated by the soma (gray) to generate egg chambers. Developing egg chambers will have one germ cell that becomes the oocyte (yellow), and the other germ cells will be support cells (blue). (B) Schematic of Nipped-A function. Nipped-A (teal) can associate with transcriptional activators (light green) to recruit SAGA and Tip60 complexes. These complexes can acetylate lysines on histones (dark green circle) to regulate transcription (dark green arrow). Nipped-A cartoon is based on the Cryo-EM structure of Tra1 in SAGA complex in Pichia pastoris yeast (Sharov et al., 2017). (C, C′) Control and (D, D′) germline-depleted Nipped-A (RNAi line #1) germaria stained with Vasa (blue) and 1B1 (red). Germaria depleted of Nipped-A show accumulation of single cells (yellow dashed line). 1B1 channel is shown in C′ and D′. (E) Quantitation of the number of single cells in germaria of control and germline-depleted Nipped-A using three RNAi lines (34.64 ± 15.04 in Nipped-A RNAi #1, 27.96 ± 12.17 in Nipped-A RNAi #2, and 12.56 ± 4.94 in Nipped-A RNAi #3 compared with 3.04 ± 0.68 in UAS-Dcr2;nosGAL4 control; n = 25 for all, ****P < 0.0001). (F, F′) Control and (G, G′) germline-depleted Nipped-A germaria stained with pMAD (green), Vasa (blue), and 1B1 (red). Germaria depleted of Nipped-A do not accumulate pMAD-positive germ cells (yellow dashed circle) (n = 20 for both, P < 0.0001). pMAD channel is shown in F′ and G′. (H, H′) Control and (I, I′) germline-depleted Nipped-A germaria stained with BamC (red) and Vasa (blue). Germaria depleted of Nipped-A do not accumulate BamC-positive germ cells (yellow dashed line in control) (n = 25 for both). BamC channel is shown in H′ and I′. (J, J′) Control and (K, K′) pgcGFP with Nipped-A germline-depletion germaria stained with GFP (green), Vasa (blue), and 1B1 (red). Germaria depleted of Nipped-A accumulate a higher number of Pgc-positive germ cells (n = 25 for both, P < 0.0001). Pgc expression is marked by GFP (yellow dashed circle/line in control and knockdown, respectively). GFP channel is shown in J′ and K′. Statistical analysis performed with Student’s t test for all except for Chi-square for H–I′. Scale bar for all images is 20 μm.