Fig. 6. Purified gonocyte culture with or without FGF9 demonstrates direct pro-survival effect of FGF9 on XY gonocytes. Gonocytes of 10.5 dpc (A) or 11.5 dpc (B) Oct4:GFP or XXSry^Myc;Oct4:GFP embryos were purified (>95%) and cultured in DMEM alone or in DMEM + FGF9 (25 ng/ml). (A) XX and XY gonocytes (10.5 dpc) decline rapidly in number regardless of treatment. (B) XX and XY gonocytes (11.5 dpc) in DMEM also decline rapidly as do XX gonocytes in DMEM + FGF9. However, XY gonocytes and XXSry^Myc gonocytes in DMEM + FGF9 exhibit significantly improved survival after 18 and 36 hours in culture (n=10 for each time point; P<0.001). (C) Alkaline phosphatase staining of XXSry^Myc; Fgf9^+/– and XXSry^Myc; Fgf9^–/– gonads at 11.5 and 12.5 dpc. XXSry^Myc; Fgf9^–/– gonads at 12.5 dpc show reduced numbers of germ cells (n3 for each sample).