Fig. 3. Characterization of the proximal homology region of Pax2. (A) Constructs and statistical overview of transgenic embryos. Transgene #6 was expressed in the MHB region and kidney of midgestation embryos both in the presence (#6a) or absence (#6b) of the Pax2 promoter (broken lines). A, ApaI; Af, AflII; Av, AvaI; B, BsrD1; K, KpnI; N, NarI; S, SphI; Sc, ScaI; Ps, PshAI; X, XmnI. (B-F) X-Gal staining of representative transgenic embryos. Strong staining was observed at the MHB for all transgenes up to construct #11 (B,C), whereas the minimal 410 bp NarI-ApaI fragment of transgene #14 (E) gave rise to reduced and more variable staining at the MHB. The activity of the MHB-specific enhancer was lost upon removal of the Pax2/5/8-binding site (S1) by either 3' deletion (D) or point mutation (F). Ectopic staining was frequently observed in the hindlimb (hl) and mesenchymal tissue of the trunk. fl, forelimb.