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Constitutive expression of a complement-like protein in toll and JAK gain-of-function mutants of Drosophila.

ABSTRACT: We show that Drosophila expresses four genes encoding proteins with significant similarities with the thiolester-containing proteins of the complement C3/alpha(2)-macroglobulin superfamily. The genes are transcribed at a low level during all stages of development, and their expression is markedly up-regulated after an immune challenge. For one of these genes, which is predominantly expressed in the larval fat body, we observe a constitutive expression in gain-of-function mutants of the Janus kinase (JAK) hop and a reduced inducibility in loss-of-function hop mutants. We also observe a constitutive expression in gain-of-function Toll mutants. We discuss the possible roles of these novel complement-like proteins in the Drosophila host defense.

SUBMITTER: Lagueux M

PROVIDER: S-EPMC17216 | biostudies-literature | 2000 Oct

REPOSITORIES: biostudies-literature

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Constitutive expression of a complement-like protein in toll and JAK gain-of-function mutants of Drosophila.

Lagueux M M Perrodou E E Levashina E A EA Capovilla M M Hoffmann J A JA

Proceedings of the National Academy of Sciences of the United States of America 20001001 21

We show that Drosophila expresses four genes encoding proteins with significant similarities with the thiolester-containing proteins of the complement C3/alpha(2)-macroglobulin superfamily. The genes are transcribed at a low level during all stages of development, and their expression is markedly up-regulated after an immune challenge. For one of these genes, which is predominantly expressed in the larval fat body, we observe a constitutive expression in gain-of-function mutants of the Janus kin ...[more]

PMID: 11027343

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Project description:BACKGROUND:X-linked protoporphyria (XLP) (MIM 300752) is an erythropoietic porphyria due to gain-of-function mutations in the last exon (Ducamp et al., Hum Mol Genet 22:1280-88, 2013) of the erythroid-specific aminolevulinate synthase gene (ALAS2). Five ALAS2 exon 11 variants identified by the NHBLI Exome sequencing project (p.R559H, p.E565D, p.R572C, p.S573F and p.Y586F) were expressed, purified and characterized in order to assess their possible contribution to XLP. To further characterize the XLP gain-of-function region, five novel ALAS2 truncation mutations (p.P561X, p.V562X, p.H563X, p.E569X and p.F575X) were also expressed and studied. METHODS:Site-directed mutagenesis was used to generate ALAS2 mutant clones and all were prokaryotically expressed, purified to near homogeneity and characterized by protein and enzyme kinetic assays. Standard deviations were calculated for 3 or more assay replicates. RESULTS:The five ALAS2 single nucleotide variants had from 1.3- to 1.9-fold increases in succinyl-CoA Vmax and 2- to 3-fold increases in thermostability suggesting that most could be gain-of-function modifiers of porphyria instead of causes. One SNP (p.R559H) had markedly low purification yield indicating enzyme instability as the likely cause for XLSA in an elderly patient with x-linked sideroblastic anemia. The five novel ALAS2 truncation mutations had increased Vmax values for both succinyl-CoA and glycine substrates (1.4 to 5.6-fold over wild-type), while the Kms for both substrates were only modestly changed. Of interest, the thermostabilities of the truncated ALAS2 mutants were significantly lower than wild-type, with an inverse relationship to Vmax fold-increase. CONCLUSIONS:Patients with porphyrias should always be assessed for the presence of the ALAS2 gain-of-function modifier variants identified here. A key region of the ALAS2 carboxyterminal region is identified by the truncation mutations studied here and the correlation of increased thermolability with activity suggests that increased molecular flexibility/active site openness is the mechanism of enhanced function of mutations in this region providing further insights into the role of the carboxyl-terminal region of ALAS2 in the regulation of erythroid heme synthesis.

Project description:Comparison between transcriptomes of dash mutants vs WT plants and ectopic expression of 35S::DASH in hairy roots versus empty vector Loss of function: 3 WT plants A17 at 8 days after pollination and 3 dash mutant plants at 8 days afer pollination. Gain of function transformants: 3 transformed plants containing empty vector and 4 transformed plants containing 35S::DASH Total RNA was extracted using a modified cetyltrimethylammonium bromide method (Verdier et al., 2008). 5ug of total RNA from each sample was purified (RNeasy MinElute Cleanup kit; Qiagen) according to the manufacturer?s instructions. RNA was quantified and evaluated for purity using an ND-1000 Nanodrop Spectrophotometer (NanoDrop Technologies) and a Bioanalyzer 2100 (Agilent). The Affymetrix M. truncatula GeneChip Array (Affymetrix) was used for expression analysis during seed development. RNA from three (for dash mutant analysis) and four (for DASH ectopic expression analysis) independent biological replicates were analysed for each time point. Probe synthesis/labelling was carried out from 500 ng of RNA using the GeneChip 3?IVT express kit, according to the manufacturer?s instructions (Affymetrix). Array hybridization, scanning, and data normalization were performed as described by Benedito et al., (2008). Each file from the hybridized Affymetrix array was exported from GeneChip Operating Software version 1.4 (Affymetrix) and imported into Robust Multiarray Average Express (Irizarry et al., 2003) for global normalization. Presence/absence call for each probe set to remove background noise was obtained using dCHIP (Li and Wong, 2001). To identify probe sets differentially expressed in dash mutant vs WT control, the R package Anapuce (J. Aubert, UMR 518 AgroParisTech/INRA) was used. For each probe set, a paired t-test was performed on the log2 expression data from three arrays (3 independent biological repeats for 8 dap data), assuming that the variance of the log expression was the same for all transcripts per genotype. Spots with extreme specific variance, too low or too high, were excluded from the statistical analysis (details on the procedure given in Gagnot et al., 2008). P-values were adjusted by the Benjamini-Hochberg method (Benjamini and Hochberg, 1995), which controls the family-wise error rate.

Dataset Information

Constitutive expression of a complement-like protein in toll and JAK gain-of-function mutants of Drosophila.

Publications

Constitutive expression of a complement-like protein in toll and JAK gain-of-function mutants of Drosophila.

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