Fig. 3. Positions of ectopic PGCs in frozen sections or whole isolated gonads at E13.5. (A) Cryostat section through a Bax^+/+ embryo. SC, spinal cord; ML, midline mesenchyme; GM, gonad mesentery; G, gut. Almost all the germ cells are in the gonad, which can be seen as a GFP+ mass of cells at the end of the gonad mesentery. Occasional cells are found in the midline mesenchyme (arrow), and around the junction of the gonad and its mesentery (right hand side of whole gonad shown in the inset). (B,C) Whole isolated gonads from female (B) and male (C) Bax^-/- embryos, showing ectopic PGCs at the hilus of the gonad, similar to the Bax^+/+ embryos. In addition, Bax^-/- embryos have groups of ectopic PGCs at other locations, including the gut mesentery (D), gonad mesentery and midline mesenchyme (E) and spinal cord (F). In each location, PGCs were also positive for alkaline phosphatase staining, shown for a group of cells in the spinal cord (G-I; enlargement of boxed area in F; green, GFP; red, alkaline phosphatase; yellow, merged images). Scale bars: 160 µm in A (inset 174 µm); 215 µm in B,C; 115 µm in D-F; 163 µm in E; 53 µm in G-I.