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Pdm1/nub repression of innate immunity

ABSTRACT: Innate immune responses rely on expression of potent effector molecules, such as antimicrobial peptides, which have the capability to kill invading microorganisms. The presence and recognition of microbial components triggers several signaling pathways, such as the Toll and IMD pathways, which in turn activate NF-kB/Rel transcription factors to induce transcription of a large number of immune system genes. Not much is known how these genes are kept silent in healthy flies in the presence of commensal microorganisms, and how the expression of immune defense genes is turned off. We found that several immune defense genes are constitutively active in nub[1] mutants, indicating that the POU domain transcription factor Pdm1/Nubbin may act as a repressor of immune gene expression. We used microarrays to analyze the global changes in gene expression in nub[1] mutants compared to wild type. To analyze changes in gene expression in the gut distinctly from other immune-responsive tissues, such as fat body and hemocytes, flies were dissected and the gut was analyzed separately from the rest of the fly (carcass). A large number of genes were differentially expressed in nub[1] mutants compared to wild type. The differentially expressed transcripts are dominated by genes involved in Immune system processes and in Metabolism/Catabolism processes. The gut samples were dominated by genes involved in biological processes linked to Metabolism/Catabolism, but also here, genes involved in Response processes were enriched among the differentially expressed genes.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE44234 | GEO | 2013/09/06

SECONDARY ACCESSION(S): PRJNA189223

REPOSITORIES: GEO

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Project description:Innate immune responses rely on expression of potent effector molecules, such as antimicrobial peptides, which have the capability to kill invading microorganisms. The presence and recognition of microbial components triggers several signaling pathways, such as the Toll and IMD pathways, which in turn activate NF-kB/Rel transcription factors to induce transcription of a large number of immune system genes. Not much is known how these genes are kept silent in healthy flies in the presence of commensal microorganisms, and how the expression of immune defense genes is turned off. We found that several immune defense genes are constitutively active in nub[1] mutants, indicating that the POU domain transcription factor Pdm1/Nubbin may act as a repressor of immune gene expression. We used microarrays to analyze the global changes in gene expression in nub[1] mutants compared to wild type. To analyze changes in gene expression in the gut distinctly from other immune-responsive tissues, such as fat body and hemocytes, flies were dissected and the gut was analyzed separately from the rest of the fly (carcass). A large number of genes were differentially expressed in nub[1] mutants compared to wild type. The differentially expressed transcripts are dominated by genes involved in Immune system processes and in Metabolism/Catabolism processes. The gut samples were dominated by genes involved in biological processes linked to Metabolism/Catabolism, but also here, genes involved in Response processes were enriched among the differentially expressed genes. The following Drosophila melanogaster strains were used: OregonR was used as wild type control and nub[1] b[1] pr[1] was used as the nub[1] mutant. Flies were dissected so that gut tissue was analyzed separately (gut) from the rest of the fly, minus head and gut (carcass). In total, 12 samples consisting of four different sample types: wt gut, wt carcass, nub[1] gut and nub[1] carcass, and three samples of each type.

Project description:The intricate regulation of gut homeostasis is dependent on a fine-tuned regulation of the host defense to avoid detrimental immune activation. We have previously applied Drosophila to show that mutants of the short isoform of the POU transcription factor Pdm1/nubbin (nub) have a constitutively active immune response, altered gut microbiota and shortened lifespan. Here, we studied the role of Nub-PB, the larger isoform derived from the nub gene. Both Nub protein isoforms contain the C-terminal POU and Homeo domains whereas Nub-PB encompasses a longer N-terminal end. Microarray analysis revealed that targeted misexpression of Nub-PB in immunocompetent organs triggers a strong and broad expression of immune genes in a comparable manner to Nub-PD mutants. The seemingly antagonistic functions of the two isoforms were confirmed by co-overexpression of both forms, which resulted in normal expression levels of antimicrobial peptide (AMP) genes. Cell line experiments demonstrated a synergistic activation of AMPs by the combined transfection with Nub-PB and NF-kB/Relish. In agreement with this finding, Relish was indispensable for Nub-PB-driven diptericin expression, suggesting that Nub-PB acts as a Relish co-activator. Moreover, Nub-PB triggered strong expression of gut-specific drosomycin-like genes in a JAK/STAT pathway-dependent manner. Using RNA interference, we found that Nub-PB influences antimicrobial peptide expression in gut but not fat body tissues. Moreover, Nub-PB expression levels in gut enterocytes correlated with the gut bacterial load as well as host lifespan, suggesting a profound role in host immunity. Surprisingly, Nub-PB-overexpression caused a hypersensitive infection phenotype as flies succumbed within 24 h to orally administered Erwinia carotovora carotovora 15. Nub-PB thus appears to be a central activator of gut immunity that requires tight control, executed at least in part, by isoform antagonism to maintain immune homeostasis.

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Pdm1/nub repression of innate immunity

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