Just as C. elegans HIF-1 activates a set of target genes, mammalian HIF can activate VEGF to promote CHIR-99021 in vivo tumor angiogenesis ( Kaelin and Ratcliffe, 2008 and Semenza, 2010). Given that HIF proline hydroxylases and H2S are emerging as promising pharmaceutical targets for a wide spectrum of human diseases—including reperfusion injury, ischemia, neurodegenerative diseases, and malignant cancer ( Kimura, 2010, Li et al., 2011, Olson, 2011, Quaegebeur and Carmeliet, 2010 and Szabó, 2007)—the link we have established

from H2S and CYSL-1 to the inhibition of EGL-9 might lead to novel therapeutic strategies to treat these disorders. Our analyses of the physiological function and evolution of CYSL-1 also provide surprising insights into how an ancient metabolic enzyme might have been co-opted during evolution to perform a novel AZD8055 ic50 function in intracellular signal transduction. CYSL-1 is more closely related to bacterial and plant cysteine synthases than to animal type-II PLP-dependent enzymes. Instead of forming a CS complex with an OAS acetyltransferase, C. elegans CYSL-1 apparently binds the

EGL-9 C terminus via an interface derived from an ancient interaction module between OASS and SAT in plants and bacteria. Such a shift in or acquisition of a new gene function, termed “gene co-option,” is a salient feature of genome evolution and can drive formation of novel biological traits that are selected ( True and Carroll, 2002). Of CYSL-1 and its five C. elegans paralogs, ZC373.1

is more similar to eukaryotic CBS proteins, whereas CYSL-1, R08E5.2, and F59A7.9 whatever form another homologous group related only distantly to their pro- and eukaryotic counterparts ( Figure 5A). Thus, the cysl-1 gene family might have divergently evolved and hence accommodated newly acquired functions beyond its metabolic roles in bacteria and plants. Interestingly, the expansion of the CBS protein family in nematodes and acquisition of CYSL-1-binding motifs in EGL-9 homologs appear to have coevolved ( Figure S7J) and occurred in a period approximately coincidental with anoxic H2S release on Earth during the Permian-Triassic mass extinction ( Grice et al., 2005). Co-option of CYSL-1 from an ancient sulfide-related metabolic enzyme into a cell-signaling mediator might have had adaptive value, enabling animals to efficiently couple decreased O2 and increased H2S levels under hypoxia or other adverse environmental conditions with enhanced cellular protection and behavioral flexibility for better survival and reproduction. To screen for mutations that activate the HIF-1 target gene reporter nIs470, we mutagenized otherwise wild-type animals carrying the K10H10.2::GFP transgene with EMS and observed the F2 progeny using a fluorescence dissecting microscope. Animals with constitutively bright GFP fluorescence under conditions of normoxia (21% O2) were isolated. Such mutants defined alleles of egl-9, vhl-1 and rhy-1.