Fig. 1. Isolation of Pax2-expressing mid-hindbrain cells from mouse embryos. (A) Structure of the Pax2^GFP BAC transgene, which was previously described as transgene 30 containing an in-frame GFP insertion in exon 2 of Pax2 (Pfeffer et al., 2002). (B) GFP expression of the Pax2^GFP transgene in the mid-hindbrain boundary (mhb) region, otic placode (op) and tail bud (tb) of E8.5 embryos. (C) Representative FACS sorting of Pax2-expressing mid-hindbrain cells. The mid-hindbrain domain (indicated by a bracket in B) was manually dissected from a control wild-type and transgenic Pax2^GFP Pax2^–/– embryo at E8.5 (seven somites) and dissociated into single cells by trypsin digestion. Live PI^– GFP⁺ cells were isolated from individual embryos by fluorescence-activated cell sorting (FACS). The percentage of GFP⁺ cells located within the sorting gate is shown for control and transgenic embryos. PI, propidium iodide.