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Activation of Insect Phenoloxidase after Injury: Endogenous versus Foreign Elicitors
Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
2009 (English)In: Journal of Innate Immunity, ISSN 1662-811X, Vol. 1, no 4, 301-308 p.Article in journal (Refereed) Published
Abstract [en]

The enzyme phenoloxidase (PO) is one of the first immune molecules that was identified in invertebrates. Recently, the immune function of PO has been challenged. We tested how PO is activated following injury in 2 insects, i.e. the fruit fly Drosophila melanogaster and the wax moth Galleria mellonella. Rapid PO activation in Drosophila was limited to discrete areas of the hemolymph clot which forms after injury. Surprisingly, unlike systemic PO activation during bacterial sepsis, clot melanization was not sensitive to microbial elicitors in our assay. Instead, Drosophila clot melanization was activated by endogenous signals such as apoptotic cells and was superinduced by phosphatidylserine, a negatively charged phospholipid normally found on the inner surface of the plasma membrane and exposed during apoptosis. In contrast, melanization in G. mellonella hemolymph was stronger and more uniform and was sensitive to peptidoglycan. This shows that both exogenous and endogenous signals can trigger the same immune mechanism in species and context-dependent ways. Our findings have implications for the evolutionary dynamics of immune mechanisms and are in agreement with recent comparisons of insect immune transcriptomes.

Place, publisher, year, edition, pages
2009. Vol. 1, no 4, 301-308 p.
Keyword [en]
Coagulation, Comparative immunology, Drosophila melanogaster, Hemostasis, Innate immunity, Insects, Pattern recognition, Sepsis, Wound healing
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:su:diva-59964DOI: 10.1159/000168009ISI: 000268091500004OAI: oai:DiVA.org:su-59964DiVA: diva2:432541
Note
authorCount :4Available from: 2011-08-04 Created: 2011-08-02 Last updated: 2012-02-15Bibliographically approved
In thesis
1. Genetic and molecular dissection of hemolymph coagulation and melanization in Drosophila melanogaster
Open this publication in new window or tab >>Genetic and molecular dissection of hemolymph coagulation and melanization in Drosophila melanogaster
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Injury to epithelial barriers puts metazoans at risk of loss of body fluid and contamination of their body by foreign particles. This risk is even exacerbated in insects, which have an open circulatory system and as a result, quickly need to seal wounds in order to keep a fairly constant internal milieu. Due to paucity of information on biochemical and molecular basis of insects’ clot, we studied how hemolymph of Drosophila melanogaster forms a clot, leading to a better understanding of responses after injury or infection in flies.

By comparing hemolymph of Drosophila after bleeding with that described for an earlier model Galleria mellonella, we showed that a bona fide clot forms in Drosophila. The Drosophila clot is a fibrous network of crosslinked hemolymph proteins, which incorporates blood cells (plasmatocytes) extending shorter cellular processes of filopodia compared to cells outside the clot. Also, some plasmatocytes in the clot show features of apoptotic death while other blood cells (crystal cells) quickly rupture.

The clot sequesters bacteria, as bacteria tethered to clot did not move. Clotting factors isolated include, Hemolectin (Hml) previously implicated in clotting, the immune induced protein Fondue and hemolymph proteins such as apolipophorin 2, fat body protein 1 and larval serum protein 1 γ. Hml mutants were more susceptible to infections when tested in a genetically sensitized background, suggesting that the clot may contribute to innate immunity. Clot also formed in hemolymph without phenoloxidase, an enzyme required for melanization and previously thought to be important for clot formation. However, we found that PO activity strengthens the clot to form a more solid plug.

We found PO activity in clot to be induced in a transcription independent manner by inner membrane phospholipids: phosphatidylserine (PS) and phosphatidylinositol (PI) exposed on dead plasmatocytes and ruptured crystal cells. This is in contrast to induction of the enzyme during infection, which requires microbial components and transcriptional induction. However, both activation of PO in the clot and activation after infection appear to depend on proteases. Surprisingly, neither PS nor PI induced PO activity in the lepidopteran Galleria mellonella, in which the enzyme activity was instead induced by the microbial components peptidoglycan. This result may caution against generalizations of findings from using only one particular insect species. Finally, we found that the rupture of crystal cell during clot formation requires the Drosophila TNF homologue Eiger, JNK homologue Basket and small GTPases. This work therefore adds hemolymph clotting to the responses after injury or infection in flies and largely establishes Drosophila as a model to study coagulation of insect hemolymph. This will lead to a more comprehensive picture of Drosophila immunity with implications for other innate immune systems including our own.

Place, publisher, year, edition, pages
Stockholm: Institutionen för molekylärbiologi och funktionsgenomik, 2007. 1-30, 36-49 p.
National Category
Biochemistry and Molecular Biology
Research subject
Molecular Biology
Identifiers
urn:nbn:se:su:diva-7046 (URN)978-91-7155-497-0 (ISBN)
Public defence
2007-09-28, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of doctoral defence the following paper was unpublished and had a status as follows: Paper 5: ManuscriptAvailable from: 2007-09-06 Created: 2007-08-31 Last updated: 2012-02-15Bibliographically approved

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