Fig. 6. The requirement of tkv for clonal expansion of GSCs during niche formation. Both germaria are labeled for lacZ (red), Hts (green) and DNA (blue). lacZ-negative mutant tkv PGCs were generated before the late third instar larval stage, and mutant tkv GSCs in the adult ovary were subsequently identified by loss of lacZ expression. (A) A germarium carrying three lacZ-positive wild type GSCs (outlined by unbroken lines) and lacZ-negative tkv mutant germline cysts (outlined by a broken line). The mutant tkv cysts were most likely derived from a lost mutant tkv GSC. (B) A germarium carrying a lacZ-negative tkv mutant GSC (outlined by a broken line), a lacZ-positive wild type GSC (outlined by an unbroken line), and a mutant tkv cyst (arrow). Scale bar: 10 µm.