The molecular archaeology of a mitochondrial death effector: AIF in Drosophila

Abstract

Apoptosis-inducing factor (AIF) is a phylogenetically conserved redox-active flavoprotein that contributes to cell death and oxidative phosphorylation in Saccharomyces cerevisiae, Caenorhabditis elegans, mouse and humans. AIF has been characterized as a caspase-independent death effector that is activated by its translocation from mitochondria to the cytosol and nucleus. Here, we report the molecular characterization of AIF in Drosophila melanogaster, a species in which most cell deaths occur in a caspase-dependent manner. Interestingly, knockout of zygotic D. melanogaster AIF (DmAIF) expression using gene targeting resulted in decreased embryonic cell death and the persistence of differentiated neuronal cells at late embryonic stages. Although knockout embryos hatch, they undergo growth arrest at early larval stages, accompanied by mitochondrial respiratory dysfunction. Transgenic expression of DmAIF misdirected to the extramitochondrial compartment (DN-DmAIF), but not wild-type DmAIF, triggered ectopic caspase activation and cell death. DN-DmAIF-induced death was not blocked by removal of caspase activator Dark or transgenic expression of baculoviral caspase inhibitor p35, but was partially inhibited by Diap1 overexpression. Knockdown studies revealed that DN-DmAIF interacts genetically with the redox protein thioredoxin-2.In conclusion, we show that Drosophila AIF is a mitochondrial effector of cell death that plays roles in developmentally regulated cell death and normal mitochondrial function.

Tousled-like kinase mediated a new type of cell death pathway in Drosophila

“…AIF is a mediator of caspase-independent cell death in Drosophila. 18 We found that loss-of-function of AIF had no effect on the cell death in GMR4tlk flies; a similar effect was observed with the p53 mutant or overexpression of ROS chelating enzymes (catalase and GTPx-1) ( Figure 4E). …”

“…16,18 We observed that inhibition of the JNK pathway by overexpression of a dominant-negative Bsk (Bsk DN ) did not suppress the eye defect of GMR4tlk flies ( Figure 4C). Consistently, the JNK pathway was not activated in the eye disc of GMR4tlk flies as determined by puc-lacZ, an in vivo reporter of JNK activation 39 ( Figure 4D a-b).…”

“…16,17 Moreover, Drosophila AIF (apoptosisinducing factor)-mediated cell death is also independent of the canonical caspase pathway. 18 Autophagic cell death has been described to participate in Drosophila embryogenesis and is involved in the removal of the salivary gland and midgut tissues during Drosophila metamorphosis. [19][20][21] Beyond development, cell death has important roles in human diseases.…”

No death without life: vital functions of apoptotic effectors

“…81 This is remarkable because, in mammalian cells, AIF depletion causes mostly a defect in respiratory complex I, indicating a major phylogenetic conservation of the contribution of AIF to optimal mitochondrial function. As an aside, it should be noted that the knockout of the D. melanogaster homolog of aif1 also causes a major respiratory defect, 73 underscoring the importance of AIF in normal mitochondrial function.…”

“…72 Apoptosis-inducing factor (AIF) is a phylogenetically ancient protein essential for survival. 73 Murine AIF is synthesized from a nuclear gene as an immature precursor with a B100 amino-acid long N-terminal mitochondrial localization signal (MLS). Upon import into mitochondria, the MLS is removed and AIF inserts into the IM via an N-terminal transmembrane region.…”