Herbivory: caterpillar saliva beats plant defences

Blood-feeding arthropods secrete special salivary proteins that suppress the defensive reaction they induce in their hosts. This is in contrast to herbivores, which are thought to be helpless victims of plant defences elicited by their oral secretions. On the basis of the finding that caterpillar regurgitant can reduce the amount of toxic nicotine released by the tobacco plant Nicotiana tabacum, we investigate here whether specific salivary components from the caterpillar Helicoverpa zea might be responsible for this suppression. We find that the enzyme glucose oxidase counteracts the production of nicotine induced by the caterpillar feeding on the plant.     

Draper-dependent glial phagocytic activity is mediated by Src and Syk family kinase signalling

The cellular machinery promoting phagocytosis of corpses of apoptotic cells is well conserved from worms to mammals. An important component is the Caenorhabditis elegans engulfment receptor CED-1 (ref. 1) and its Drosophila orthologue, Draper. The CED-1/Draper signalling pathway is also essential for the phagocytosis of other types of 'modified self' including necrotic cells, developmentally pruned axons and dendrites, and axons undergoing Wallerian degeneration. Here we show that Drosophila Shark, a non-receptor tyrosine kinase similar to mammalian Syk and Zap-70, binds Draper through an immunoreceptor tyrosine-based activation motif (ITAM) in the Draper intracellular domain. We show that Shark activity is essential for Draper-mediated signalling events in vivo, including the recruitment of glial membranes to severed axons and the phagocytosis of axonal debris and neuronal cell corpses by glia. We also show that the Src family kinase (SFK) Src42A can markedly increase Draper phosphorylation and is essential for glial phagocytic activity. We propose that ligand-dependent Draper receptor activation initiates the Src42A-dependent tyrosine phosphorylation of Draper, the association of Shark and the activation of the Draper pathway. These Draper-Src42A-Shark interactions are strikingly similar to mammalian immunoreceptor-SFK-Syk signalling events in mammalian myeloid and lymphoid cells. Thus, Draper seems to be an ancient immunoreceptor with an extracellular domain tuned to modified self, and an intracellular domain promoting phagocytosis through an ITAM-domain-SFK-Syk-mediated signalling cascade.     

A paracrine requirement for hedgehog signalling in cancer

Ligand-dependent activation of the hedgehog (Hh) signalling pathway has been associated with tumorigenesis in a number of human tissues. Here we show that, although previous reports have described a cell-autonomous role for Hh signalling in these tumours, Hh ligands fail to activate signalling in tumour epithelial cells. In contrast, our data support ligand-dependent activation of the Hh pathway in the stromal microenvironment. Specific inhibition of Hh signalling using small molecule inhibitors, a neutralizing anti-Hh antibody or genetic deletion of smoothened (Smo) in the mouse stroma results in growth inhibition in xenograft tumour models. Taken together, these studies demonstrate a paracrine requirement for Hh ligand signalling in the tumorigenesis of Hh-expressing cancers and have important implications for the development of Hh pathway antagonists in cancer.     

Production of the antimalarial drug precursor artemisinic acid in engineered yeast

Malaria is a global health problem that threatens 300-500 million people and kills more than one million people annually. Disease control is hampered by the occurrence of multi-drug-resistant strains of the malaria parasite Plasmodium falciparum. Synthetic antimalarial drugs and malarial vaccines are currently being developed, but their efficacy against malaria awaits rigorous clinical testing. Artemisinin, a sesquiterpene lactone endoperoxide extracted from Artemisia annua L (family Asteraceae; commonly known as sweet wormwood), is highly effective against multi-drug-resistant Plasmodium spp., but is in short supply and unaffordable to most malaria sufferers. Although total synthesis of artemisinin is difficult and costly, the semi-synthesis of artemisinin or any derivative from microbially sourced artemisinic acid, its immediate precursor, could be a cost-effective, environmentally friendly, high-quality and reliable source of artemisinin. Here we report the engineering of Saccharomyces cerevisiae to produce high titres (up to 100 mg l(-1)) of artemisinic acid using an engineered mevalonate pathway, amorphadiene synthase, and a novel cytochrome P450 monooxygenase (CYP71AV1) from A. annua that performs a three-step oxidation of amorpha-4,11-diene to artemisinic acid. The synthesized artemisinic acid is transported out and retained on the outside of the engineered yeast, meaning that a simple and inexpensive purification process can be used to obtain the desired product. Although the engineered yeast is already capable of producing artemisinic acid at a significantly higher specific productivity than A. annua, yield optimization and industrial scale-up will be required to raise artemisinic acid production to a level high enough to reduce artemisinin combination therapies to significantly below their current prices.     

Topical drug rescue strategy and skin protection based on the role of Mc1r in UV-induced tanning

Ultraviolet-light (UV)-induced tanning is defective in numerous 'fair-skinned' individuals, many of whom contain functional disruption of the melanocortin 1 receptor (MC1R). Although this suggested a critical role for the MC1R ligand melanocyte stimulating hormone (MSH) in this response, a genetically controlled system has been lacking in which to determine the precise role of MSH-MC1R. Here we show that ultraviolet light potently induces expression of MSH in keratinocytes, but fails to stimulate pigmentation in the absence of functional MC1R in red/blonde-haired Mc1r(e/e) mice. However, pigmentation could be rescued by topical application of the cyclic AMP agonist forskolin, without the need for ultraviolet light, demonstrating that the pigmentation machinery is available despite the absence of functional MC1R. This chemically induced pigmentation was protective against ultraviolet-light-induced cutaneous DNA damage and tumorigenesis when tested in the cancer-prone, xeroderma-pigmentosum-complementation-group-C-deficient genetic background. These data emphasize the essential role of intercellular MSH signalling in the tanning response, and suggest a clinical strategy for topical small-molecule manipulation of pigmentation.