Viral Immune Response in Drosophila
A common question until late 2005 was whether viruses infect insects, and if they do, how do the insects defend against the viruses. This question was answered by a French research group, where it was found that the Jak-stat pathway (on the right hand most side of the diagram from the post titles "Drosophila Immunity) had conserved functions in the Drosophila anti-viral response.
The virus used was the Drosophila C virus, DCV, which is an RNA virus in the same family as polio and foot-and-mouth disease. Depending on the dose, injected DCV can kill a fly within 4-10 days. Interstingly, ingestion of the virus does not make the flies sick. As such, the natural of DCV infection of Drosophila is unkown. Upon injection with DCV, approximately 140 genes are upregulated by at least two fold. Ingestion of DCV leads to the upregulation of only 10 genes. Of the 140 genes induced, only one third are common to those induced during bacterial or fungal infection, indicating that the Jak-Stat pathway may defend against viruses independently of the Imd or Toll pathways. In mammals, Jak-Stat pathways are responsible for T cell activation in aquired immunity as well as viral defense. While Drosophila only have one Jak-Stat pathway, it is unsurprising that it shares homology to mammalian Jak-Stats or that it is involved in viral immunity.
That Jak-Stat pathway, however, is not solely responsible for the Drosophila viral response. Not all of the 140 genes induced upon injection with DCV are Jak-Stat dependent. Moreover, activation of genes in response to another virus, the Flock House virus, are also independent of the Jak-Stat pathway. What is puzzling is that mutant flies with a lethal allele of Hopscotch, which leads to the constitutive activation of the Jak-Stat pathway, there was no activation of the DCV induced genes, but other targets of the pathway, not induced by DCV were activated. The aurthors hypothesize that Jak-Stat pathway does not act alone, but rather has to cooperate with another pathway(s) to recognize and defend against DCV.
This, while very interesting, goes to show that even though the Drosophila genome has been sequenced, there is still much we dont know in terms of the existence and function of genes.
The virus used was the Drosophila C virus, DCV, which is an RNA virus in the same family as polio and foot-and-mouth disease. Depending on the dose, injected DCV can kill a fly within 4-10 days. Interstingly, ingestion of the virus does not make the flies sick. As such, the natural of DCV infection of Drosophila is unkown. Upon injection with DCV, approximately 140 genes are upregulated by at least two fold. Ingestion of DCV leads to the upregulation of only 10 genes. Of the 140 genes induced, only one third are common to those induced during bacterial or fungal infection, indicating that the Jak-Stat pathway may defend against viruses independently of the Imd or Toll pathways. In mammals, Jak-Stat pathways are responsible for T cell activation in aquired immunity as well as viral defense. While Drosophila only have one Jak-Stat pathway, it is unsurprising that it shares homology to mammalian Jak-Stats or that it is involved in viral immunity.
That Jak-Stat pathway, however, is not solely responsible for the Drosophila viral response. Not all of the 140 genes induced upon injection with DCV are Jak-Stat dependent. Moreover, activation of genes in response to another virus, the Flock House virus, are also independent of the Jak-Stat pathway. What is puzzling is that mutant flies with a lethal allele of Hopscotch, which leads to the constitutive activation of the Jak-Stat pathway, there was no activation of the DCV induced genes, but other targets of the pathway, not induced by DCV were activated. The aurthors hypothesize that Jak-Stat pathway does not act alone, but rather has to cooperate with another pathway(s) to recognize and defend against DCV.
This, while very interesting, goes to show that even though the Drosophila genome has been sequenced, there is still much we dont know in terms of the existence and function of genes.
posted by Sean at 4:27 PM
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