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Chronic activation of the epithelial immune system of the fruit fly's salivary glands has a negative effect on organismal growth and induces a peculiar set of target genes.

Abdelsadik A, Roeder T - BMC Genomics (2010)

Bottom Line: Gene ontology analyses of regulated genes revealed a significant increase in genes associated with ribosomal and proteasomal function.Among the regulated genes, those that code for signaling associated protease activity are significantly modulated.Although they produce antimicrobial peptides, their overall response is highly tissue-specific.

View Article: PubMed Central - HTML - PubMed

Affiliation: Christian-Albrechts-University of Kiel, Zoophysiology, Kiel, Germany.

ABSTRACT

Background: Epithelial and especially mucosal immunity represents the first line of defence against the plethora of potential pathogens trying to invade via the gastrointestinal tract. The salivary glands of the fruit fly are an indispensable part of the gastrointestinal tract, but their contribution to the mucosal immunity has almost completely been neglected. Our major goal was to elucidate if the fly's salivary glands are able to mount an immune response and what the major characteristics of this immune response are.

Results: Ectopic activation of the IMD-pathway within the salivary gland cells is able to induce an immune response, indicating that the salivary glands are indeed immune competent. This reaction is characterized by the concurrent expression of numerous antimicrobial peptide genes. In addition, ectopic activation of the salivary gland's immune response induces morphological changes such as dwarfism throughout all developmental stages and a significantly decreased length of the salivary glands themselves. DNA-microarray analyses of the reaction revealed a complex pattern of up- and downregulated genes. Gene ontology analyses of regulated genes revealed a significant increase in genes associated with ribosomal and proteasomal function. On the other hand, genes coding for peptide receptors and some potassium channels are downregulated. In addition, the comparison of the transcriptional events induced following IMD-activation in the trachea and the salivary glands shows also only a small overlap, indicating that the general IMD-activated core transcriptome is rather small and that the tissue specific component of this response is dominating. Among the regulated genes, those that code for signaling associated protease activity are significantly modulated.

Conclusions: The salivary glands are immune-competent and they contribute to the overall intestinal immune system. Although they produce antimicrobial peptides, their overall response is highly tissue-specific. Our analysis indicates that chronic activation of the salivary gland's immune system is costly, as it induces severe reduction in growth throughout development. The IMD-regulated increase in expression levels of the fly's presenilin representatives opens the opportunity to use the salivary glands for studying the physiological and pathophysiological role of these genes in a simple but functional environment.

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Using the Gal4/UAS-system, activation of the salivary glands can be achieved by genetic means. Proteins of the salivary gland secretion family are believed to be restricted to the salivary glands. Crossing the sgs3::gal4 line with a UAS::gfp responder line revealed that expression is indeed restricted to the salivary glands (A). Based on the UAS/Gal4 system for ectopic activation, the IMD-pathway, which is instrumental in epithelial immunity, can be activated by targeted overexpression of peptidoglycan recognition receptors. The membrane bound PGRP-LC activates in a cell-autonomous way, whereas the soluble PGRP-LE activates in an organ-wide, systemic way (B). If the pgrp-le gene is expressed in the salivary glands only, the antimicrobial peptide gene drosomycin (here used as a reporter for immune system activity and visualized by drosP::gfp) is expressed in defined parts of the intestine only (but not on the salivary glands) (C).
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Figure 1: Using the Gal4/UAS-system, activation of the salivary glands can be achieved by genetic means. Proteins of the salivary gland secretion family are believed to be restricted to the salivary glands. Crossing the sgs3::gal4 line with a UAS::gfp responder line revealed that expression is indeed restricted to the salivary glands (A). Based on the UAS/Gal4 system for ectopic activation, the IMD-pathway, which is instrumental in epithelial immunity, can be activated by targeted overexpression of peptidoglycan recognition receptors. The membrane bound PGRP-LC activates in a cell-autonomous way, whereas the soluble PGRP-LE activates in an organ-wide, systemic way (B). If the pgrp-le gene is expressed in the salivary glands only, the antimicrobial peptide gene drosomycin (here used as a reporter for immune system activity and visualized by drosP::gfp) is expressed in defined parts of the intestine only (but not on the salivary glands) (C).

Mentions: A major prerequisite for the current study was the ability to specifically target the salivary glands of larval flies without any confounding expression. This is required to manipulate expression of certain genes within this tissue only. Salivary gland secretion (sgs) proteins are believed to be restricted to salivary glands. To evaluate if this specific expression pattern is operational for the corresponding Gal4-lines, we used the bipartite Gal4/UAS expression control system and crossed the Gal4-driver P [Sgs3-GAL4.PD]TP1 to UAS-flies carrying gfp under control of the UAS-promotor. The expression of the GFP-protein is, as expected, exclusive for the salivary glands (Fig. 1A).


Chronic activation of the epithelial immune system of the fruit fly's salivary glands has a negative effect on organismal growth and induces a peculiar set of target genes.

Abdelsadik A, Roeder T - BMC Genomics (2010)

Using the Gal4/UAS-system, activation of the salivary glands can be achieved by genetic means. Proteins of the salivary gland secretion family are believed to be restricted to the salivary glands. Crossing the sgs3::gal4 line with a UAS::gfp responder line revealed that expression is indeed restricted to the salivary glands (A). Based on the UAS/Gal4 system for ectopic activation, the IMD-pathway, which is instrumental in epithelial immunity, can be activated by targeted overexpression of peptidoglycan recognition receptors. The membrane bound PGRP-LC activates in a cell-autonomous way, whereas the soluble PGRP-LE activates in an organ-wide, systemic way (B). If the pgrp-le gene is expressed in the salivary glands only, the antimicrobial peptide gene drosomycin (here used as a reporter for immune system activity and visualized by drosP::gfp) is expressed in defined parts of the intestine only (but not on the salivary glands) (C).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2874812&req=5

Figure 1: Using the Gal4/UAS-system, activation of the salivary glands can be achieved by genetic means. Proteins of the salivary gland secretion family are believed to be restricted to the salivary glands. Crossing the sgs3::gal4 line with a UAS::gfp responder line revealed that expression is indeed restricted to the salivary glands (A). Based on the UAS/Gal4 system for ectopic activation, the IMD-pathway, which is instrumental in epithelial immunity, can be activated by targeted overexpression of peptidoglycan recognition receptors. The membrane bound PGRP-LC activates in a cell-autonomous way, whereas the soluble PGRP-LE activates in an organ-wide, systemic way (B). If the pgrp-le gene is expressed in the salivary glands only, the antimicrobial peptide gene drosomycin (here used as a reporter for immune system activity and visualized by drosP::gfp) is expressed in defined parts of the intestine only (but not on the salivary glands) (C).
Mentions: A major prerequisite for the current study was the ability to specifically target the salivary glands of larval flies without any confounding expression. This is required to manipulate expression of certain genes within this tissue only. Salivary gland secretion (sgs) proteins are believed to be restricted to salivary glands. To evaluate if this specific expression pattern is operational for the corresponding Gal4-lines, we used the bipartite Gal4/UAS expression control system and crossed the Gal4-driver P [Sgs3-GAL4.PD]TP1 to UAS-flies carrying gfp under control of the UAS-promotor. The expression of the GFP-protein is, as expected, exclusive for the salivary glands (Fig. 1A).

Bottom Line: Gene ontology analyses of regulated genes revealed a significant increase in genes associated with ribosomal and proteasomal function.Among the regulated genes, those that code for signaling associated protease activity are significantly modulated.Although they produce antimicrobial peptides, their overall response is highly tissue-specific.

View Article: PubMed Central - HTML - PubMed

Affiliation: Christian-Albrechts-University of Kiel, Zoophysiology, Kiel, Germany.

ABSTRACT

Background: Epithelial and especially mucosal immunity represents the first line of defence against the plethora of potential pathogens trying to invade via the gastrointestinal tract. The salivary glands of the fruit fly are an indispensable part of the gastrointestinal tract, but their contribution to the mucosal immunity has almost completely been neglected. Our major goal was to elucidate if the fly's salivary glands are able to mount an immune response and what the major characteristics of this immune response are.

Results: Ectopic activation of the IMD-pathway within the salivary gland cells is able to induce an immune response, indicating that the salivary glands are indeed immune competent. This reaction is characterized by the concurrent expression of numerous antimicrobial peptide genes. In addition, ectopic activation of the salivary gland's immune response induces morphological changes such as dwarfism throughout all developmental stages and a significantly decreased length of the salivary glands themselves. DNA-microarray analyses of the reaction revealed a complex pattern of up- and downregulated genes. Gene ontology analyses of regulated genes revealed a significant increase in genes associated with ribosomal and proteasomal function. On the other hand, genes coding for peptide receptors and some potassium channels are downregulated. In addition, the comparison of the transcriptional events induced following IMD-activation in the trachea and the salivary glands shows also only a small overlap, indicating that the general IMD-activated core transcriptome is rather small and that the tissue specific component of this response is dominating. Among the regulated genes, those that code for signaling associated protease activity are significantly modulated.

Conclusions: The salivary glands are immune-competent and they contribute to the overall intestinal immune system. Although they produce antimicrobial peptides, their overall response is highly tissue-specific. Our analysis indicates that chronic activation of the salivary gland's immune system is costly, as it induces severe reduction in growth throughout development. The IMD-regulated increase in expression levels of the fly's presenilin representatives opens the opportunity to use the salivary glands for studying the physiological and pathophysiological role of these genes in a simple but functional environment.

Show MeSH
Related in: MedlinePlus