To determine how EGL-9 is modulated to control the O2-ON behavior, authors screened for mutants that resembled
egl-9 mutants. To facilitate this screen, authors constructed an integrated transgenic reporter strain (nIs470) in which a green fluorescent protein (GFP) variant (Venus) was driven by the promoter of a known HIF-1 target gene, K10H10.2.
egl-9 mutants exhibited bright GFP fluorescence throughout the animal, whereas GFP was essentially absent in
egl-9(+) and
egl-9;
hif-1 double mutants, indicating that the GFP transgene specifi- cally reports the transcriptional activity of HIF-1.