THE DROSOPHILA ZONDA GENE IS INVOLVED IN THE TRANSCRIPTIONAL RESPONSE TO HYPOXIA AND GROWTH REGULATION

NURIA M ROMERO; JUAN MANUEL GÒMEZ; PABLO WAPPNER

Buenos Aires

Congreso; 4th Internacional Meeting of the Latin American Society of Developmental Biology; 2008

Latin American Society of developmental Biology

The mammalian Hypoxia Inducible Factor (HIF) is a heterodimeric a/b transcription factor that induces a wide spectrum of genes under conditions of oxygen deprivation. The Drosophila bHLH-PAS proteins Sima and Tango function respectively as HIF1a and HIF1b homologues, being the mechanism of regulation by oxygen highly conserved in evolution. Animal growth depends on environmental conditions, including nutrient and oxygen availability, and this coordination is exerted mainly by the PI3K and TOR signaling pathways. Consistent with hypoxia being a modulator of development timing, we and others have reported that Fatiga, the main negative regulator of Sima, is required for normal growth and cell size determination. In a genetic screen for components required for the transcriptional response to hypoxia, we have identified a novel gene that we have named zonda (zda). RNAi-mediated zda silencing in S2 cells led to a decrease in Sima-dependent response to hypoxia, as revealed by the expression of a luciferase transcriptional reporter. We performed P-element imprecise excisions to generate zda null mutations, which are lethal at first larval instar, and exhibit an impaired hypoxic response. By using an available EP line, we explored the effect of zda overexpression, and found a remarkable delay of pupariation, which was further enhanced in hypoxic or starving conditions. Precise excisions of the EP element completely restored normal developmental timing, both in normoxia and in hypoxia. In wild type flies, it is known that hypoxia significantly slows down development, although this phenomenon has not been characterized in detail and the molecular mechanism involved remains obscure. We have found that Drosophila development is sensitive to hypoxia principally at third larval instar, leading to delayed pupariation. We found in addition that Sima is not responsible for this hypoxia-dependent developmental delay and consistent with this, the effect of the overexpression of zonda in a sima mutant background was identical to the one obtained upon its overexpression in wild type flies. We are currently exploring the occurrence of genetic interactions between zda and elements of the PI3K and TOR pathways.