Fig. 3. Two mechanisms used by GSCs for populating their niches. (A) An explanatory diagram for two potential mechanisms populating GSC niches: GSCs in one niche come from one PGC (top); GSCs in one niche come from multiple PGCs (bottom). PGCs are marked by gain of lacZ (nuclear) expression (B,C) or loss of lacZ (nuclear and cytoplasmic) expression (D,E) before the late third instar larval stage. (B-E) Germaria are labeled for lacZ (red), Hts (green) and DNA (blue). (B) A germarium with one lacZ-positive marked GSC (broken outline) and a lacZ-negative unmarked GSC (unbroken outline) (i.e. only some of the GSC progeny are marked by lacZ expression). (C) A germarium with three GSCs (their spectrosomes indicated by arrowheads) and their progeny are marked by lacZ expression (an overlaid image). (D) A germarium with one lacZ-negative marked GSC (broken outline) and one lacZ-positive unmarked GSC (unbroken outline) (i.e. only a fraction of differentiated germ cells are marked by loss of lacZ expression). (E) A germarium with three GSCs (broken outline) marked by the loss of lacZ expression, in which all differentiated germ cells are lacZ negative. Scale bar: 10 µm.