Fig. 4. PTEN^2L117 homozygous embryos show constitutive induction of the transgenic HRE reporter LDH-LacZ. (A) Normoxic wild-type embryos. Drosophila wild-type embryos maintained in normoxia do not express the hypoxia-inducible reporter LDH-LacZ, as revealed by X-gal staining. (B) Hypoxic wild-type embryos. Embryos were exposed to 3% O₂ for 4 hours, fixed and stained with X-gal. Induction of the LDH-LacZ reporter was observed in an expression pattern that is coincident with some of the tracheal branches (arrow) (Lavista-Llanos et al., 2002). (C) Effect of PTEN loss-of-function on HRE induction in vivo. In PTEN^2L117homozygous embryos the LDH-LacZ reporter was induced in normoxia (arrow) in a pattern that paralleled induction of the reporter in hypoxic wild-type embryos (compare with B).