Article

Regulation of midgut defensin production in the blood-sucking insect Stomoxys calcitrans

School of Biological Sciences, University of Wales, Bangor LL57 2UW, Wales, UK.
Insect Molecular Biology (Impact Factor: 2.98). 01/2002; 10(6):561-71. DOI: 10.1046/j.0962-1075.2001.00296.x
Source: PubMed

ABSTRACT The Stomoxys midgut defensin (Smd) family of genes are exclusively expressed in the anterior midgut of adult flies. Their putative function is protection of the stored bloodmeal from microbial attack. Smd genes are constitutively expressed, up-regulated in response to a bloodmeal and further up-regulated by immune stimulation per os but only in the presence of a bloodmeal not a sugar meal. Smd genes are down-regulated in response to a systemic immune challenge. Smd gene constructs transfected into l(2)mbn cells undertake constitutive expression but are not up-regulated by immune challenge. Electrophoretic mobility shift assays (EMSA) suggest the rel-like sites in the proximal promoter region of Smd genes do not bind midgut factors and so are non-functional.

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    • "Exon–intron genomic structure has been previously described for vector arthropod defensins including those of I. ricinus (Rudenko et al., 2007), O. moubata (Nakajima et al., 2002a,b), Aedes aegypti (Lowenberger et al., 1999) and Anopheles gambiae (Eggleston et al., 2000). Intronless defensins have also been previously reported in I. scapularis (Hynes et al., 2005), D. variabilis (Hynes et al., 2005) and Stomoxys calcitrans (Munks et al., 2001). We found that I. ricinus contains both variants with DefMT3 and DefMT4 containing two introns, and DefMT7 identified as being intronless. "
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    ABSTRACT: The hard-bodied tick Ixodes ricinus (castor bean tick) is the most common tick species in Europe. I. ricinus is a vector of the causative agents of diseases that affect humans and animals including tick-borne encephalitis, borreliosis, tick-borne fever and babesiosis. The innate immune system provides ticks with quite an efficient defence against some pathogenic microorganisms in the event of their penetration into the tick body or through the blood feed. Antimicrobial peptides (AMPs) constitute an important feature of the tick immune system. Defensins are a well-known class of AMPs. Members of the defensin family of proteins have been reported in several tick species. So far, only two defensins had been identified from I. ricinus. In this study, we report the identification of six novel putative defensins from I. ricinus at the genomic and transcriptional levels. At the genomic level they show differences with one being intronless, while others containing two introns. The expression pattern of these molecules in the salivary glands, midgut, ovary, malpighian tubules, haemolymph and the tick cell line IRE/CTVM19 was determined. Some of them are tissue specific while others seem to be ubiquitous. Molecular and phylogenetic analyses show that these novel members of the I. ricinus defensin family differ phylogenetically and structurally; nevertheless, the cysteine pattern is highly conserved among the family members. Finally, antimicrobial-peptide prediction tools were used to predict putative antimicrobial activity of our defensins. They show putative antimicrobial activity mainly against Gram-positive bacteria. This study displays the diversity of defensin family in the tick I. ricinus.
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    • "We examined expression of these genes in infected and uninfected fleas in a four-day time course as described above. Analysis of these experiments suggest that transcript abundance for defensin, lectin and SERPIN increase in response to feeding (defensin, P < 0.0001; lectin, P < 0.0001 and P < 0.001; serpin, P < 0.018, Table S2), which is consistent with observations for defensin gene expression in the stable fly, Stomoxys calcitrans, and the sheep tick, Ixodes ricinus (Lehane et al., 1997; Munks et al., 2001; Boulanger et al., 2002; Hamilton et al., 2002; Rudenko et al., 2005) (Table S2). Interestingly, none of these genes show a significant treatment effect on gene expression due to infection (Table S2). "
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    • "These defensins could be transcribed prior to a known bacterial challenge as was postulated for St. calcitrans midgut defensins (Munks et al., 2001). More recently, AaDefA has been shown to co-localize with phenoloxidase, suggesting a potential role for defensin in the phenoloxidase-based melanization response (Hillyer & Christensen, 2005). "
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