Fig. 1. Pgc is expressed during G2 phase in the differentiating GSC daughter.

(A) A schematic of the Drosophila female germarium. Stem cells (blue) are attached to the somatic niche (grey). The stem cells divide asymmetrically to renew and to give rise to the pre-cystoblast (pre-CB) (green). The pre-CB expresses Bam and is referred to as the cystoblast (CB) (red). The CB undergoes four incomplete rounds of divisions to give rise to a 16-cell cyst. The undifferentiated cells are marked by structures called spectrosomes while the differentiating cysts are marked by structures called fusomes. (B) The Pgc reporter (pgcGFP) was created by replacing the coding region of pgc with eGFP, leaving the pgc promoter, 5′ UTR and 3′ UTR intact. (C, C1) Germarium of pgcGFP transgenic female stained for 1B1 (red), GFP (green) and Vasa (blue). Pgc is expressed in a single cell of the germarium (white arrow), usually in the cell that is one-cell diameter away from the somatic niche (dotted line). Cells closest to the somatic niche are the germline stem cells (GSC) marked with white asterisks. (D) Quantification of cells expressing Pgc in the germaria (n=230 germaria). 24% of the germaria show pgcGFP expression and 80% of those were one cell diameter away from the niche. Later stages showed no prominent Pgc expression. (E, E1) Germarium of pgcGFP flies stained with pMAD (red), GFP (green) and 1B1 (blue). Pgc expressing cells are not positive for GSC specific marker, pMAD. GSC is marked with a yellow circle. GFP channel is shown in E1. (F, F1) Germarium of pgcGFP flies stained with differentiation marker BamC (red), GFP (green) and Vasa (blue). Pgc expressing cell (yellow circle) is not positive for Bam. BamC channel is shown in F1. White asterisk represents a GSC. (G, G1) pgcGFP; bam mutant germarium stained with GFP (green) and Vasa (blue). 23% of the CB in the bam tumor showed high levels of Pgc expression (white arrow) (n=974 cells, 12 tumors). White asterisk represents GSCs. (H) Quantification of CBs positive for both Pgc and cell cycle markers. Pgc expression correlated mostly with G2 phase markers, CycA (81% in pgcGFP, n=25 germaria and 85% in pgcGFP; bam n=220 cells) and CycB (49% in pgcGFP, n=85 germaria and 47% in pgcGFP; bam, n=200 cells). For representative images see Fig. S1B–I2. (I, I1) Germarium of CycB mutant carrying Pgc reporter stained with Vasa (blue) and GFP (green) show 70% of undifferentiated cells expressing Pgc (n=136 cells, 5 tumors). GFP channel is shown in I1. Scale: 10 µm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)