FIG. 1.

A hypoxia-inducible transcriptional response in Drosophila. Physiological characterization of the hypoxic response in vivo. (A) Schematic representation of the LDH-LacZ transcriptional reporter: A 233-bp fragment of the murine LDH-A enhancer from bp −186 to +47 (relative to the transcription initiation site) controls β-Gal expression. The sequences correspond to HRE and CRE elements present in the enhancer. Bases in bold lettering mark the HRE consensus, and the numbers above indicate the position relative to the transcription initiation site. (B) The LDH-LacZ reporter is induced in embryos maintained at 5% O₂ for 8 h (•) compared to normoxia (⧫). The x axis represents time course of the β-Gal reaction. (C and D) Stage 17 transgenic embryos carrying the LDH-LacZ reporter maintained in normoxia (C) or hypoxia (8 h at 5% O₂) (D) were stained with X-Gal in a reaction developed overnight. Whereas in embryos exposed to hypoxia the X-Gal staining was ubiquitous, in normoxic individuals the expression of the reporter was restricted to a small anterior domain. (E) Modulation of the hypoxic response during development. Individuals bearing the LDH-LacZ reporter were synchronized at different stages of development and were subjected to hypoxia (5% O₂) for 4 h. The hypoxia/normoxia β-Gal activity ratio is shown. Hypoxic induction of the reporter is maximal at late embryogenesis, although it is also high at larval stages 1 and 2. P, pupa; A, adult. (F) Effect of oxygen concentration. Stage 16 to 17 embryos bearing the LDH-LacZ reporter were exposed to different oxygen concentrations for 4 h, the β-Gal activity was compared with that of normoxic controls, and the ratios of the activities were calculated. Triplicate determinations of the activity were performed. Induction of the reporter was maximal between 3 and 5% oxygen concentration.