Unknown,Transcriptomics,Genomics,Proteomics

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Transcription profiling of C. elegans reveals heme homeostasis is regulated by the conserved and concerted functions of HRG-1 proteins

ABSTRACT: Hemes are essential but potentially cytotoxic cofactors that participate in critical and diverse biological processes. Although the pathway and intermediates for heme biosynthesis have been well defined, the intracellular networks which mediate heme trafficking remain unknown. Caenorhabditis elegans and related helminths are natural heme auxotrophs requiring environmental heme for growth and development. We exploited this auxotrophy to identify HRG-1 and HRG-4 in C. elegans and show that they are essential for heme homeostasis and normal vertebrate development. We demonstrate that heme deficiency upregulates expression of hrg-4 and its evolutionarily conserved paralog hrg-1. Depletion of either HRG-1 or HRG-4 in worms results in disruption of organismal heme sensing and abnormal response to heme analogs. HRG-1 and HRG-4 are novel transmembrane proteins that bind heme and have evolutionarily conserved functions. Transient knockdown of hrg-1 in zebrafish leads to hydrocephalus, yolk tube malformations, and, most strikingly, profound defects in erythropoiesis - phenotypes that are fully rescued by worm HRG-1. These findings reveal unanticipated and conserved pathways for cellular heme trafficking in animals that defines the paradigm for eukaryotic heme transport. Uncovering the mechanisms of heme transport in C. elegans will provide novel insights into human disorders of heme metabolism and generate unique anthelmintics to combat worm infestations. Experiment Overall Design: As a first-step toward understanding heme homeostasis at the molecular level, we performed genome-wide microarrays to identify genes that are transcriptionally regulated by heme. For microarray analysis, synchronized F2 larvae were re-inoculated in mCeHR-2 medium supplemented with 4, 20 or 500 uM hemin and harvested at the late L4 stage for mRNA prep and probe hybridization to Affymetrix C. elegans Whole Genome Expression Arrays. Total RNA from three biological replicates were used at each hemin concentration. Data from worms grown in mCeHR-2 medium with 4 and 500 uM hemin were compared to data from worms grown in 20 uM hemin. Microarray data were verified with Microarray Suite 5.0 (Affymetrix) and Robust Multichip Average Method (RMA, R package). Results from MAS 5.0 and RMA analyses provided with 375 genes that showed 1.6 fold change in 4 and 500 uM hemin when compared to data from 20 uM hemin samples. Statistical analyses identified changes in 375 genes from worms grown in either 4 or 500 ÂµM heme (see Methods). The microarray results were validated by qRT-PCR (Supplementary Fig. 1) and the 375 heme-responsive genes were classified into eight categories based on their relative changes in gene expression (Table I). The data from the microarray study show that â?°1.9 % of genes in the worm genome are transcriptionally responsive to heme. Notably, of the 375 genes, 164 had some sequence identity in human genome databases at the amino acid level, and >90 % of the genes had no ascribed function in the C.

ORGANISM(S): Caenorhabditis elegans

SUBMITTER: WeiPing Chen

PROVIDER: E-GEOD-8696 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Haem homeostasis is regulated by the conserved and concerted functions of HRG-1 proteins.

Rajagopal Abbhirami A Rao Anita U AU Amigo Julio J Tian Meng M Upadhyay Sanjeev K SK Hall Caitlin C Uhm Suji S Mathew M K MK Fleming Mark D MD Paw Barry H BH Krause Michael M Hamza Iqbal I

Nature 20080416 7198

Haems are metalloporphyrins that serve as prosthetic groups for various biological processes including respiration, gas sensing, xenobiotic detoxification, cell differentiation, circadian clock control, metabolic reprogramming and microRNA processing. With a few exceptions, haem is synthesized by a multistep biosynthetic pathway comprising defined intermediates that are highly conserved throughout evolution. Despite our extensive knowledge of haem biosynthesis and degradation, the cellular pathw ...[more]

PMID: 18418376

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Project description:Purpose: The goal of this study is to understand how dbl-1, which is made primarily in neurons, and hrg-7, which is exclusively made in the intestine, contribute to systemic heme homeostasis. Methods: mRNA profiles of late L4 dbl-1(nk3) and hrg-7(tm6801) mutant C. elegans fed OP50 E. coli or OP50 + 50µM heme were compared to mRNA profiles from wildtype (WT) broodmates. Profiles were generated with single-end 50 base reads obtained using Illumina’s HiSeq 2500. Bioinformatics quality control was performed followed by alignment of reads to the ce10 reference genome using Tophat2, version 2.1.0. We found differentially expressed genes using Cufflinks 2, version 2.2.1 with a cutoff of 0.05 on False Discovery Rate (FDR). Results: We found a substantial overlap of genes regulated by both dbl-1 and hrg-7, including 49 heme-responsive genes (hrgs) in low heme (OP50) and 11 hrgs in high heme (OP50 + 50µM). Additionally, our data indicate crosstalk between dbl-1 and hrg-7 signaling. dbl-1 directly regulates hrg-7 expression, while hrg-7 regulates three components of the dbl-1 signaling pathway. Conclusions: Our study demonstrates that communication between the neuron and intestine is essential for heme homeostasis. Specifically, we report that HRG-7 functions as a secreted signaling factor which communicates intestinal heme status with extraintestinal tissues by integrating a DBL-1/BMP -dependent response from the neurons to transcriptionally regulate genes involved in heme homeostasis. Cellular requirements for heme are fulfilled by a cell’s internal capacity to synthesize its own heme in a cell-autonomous manner. However, growing evidence in vertebrates predicts that cellular heme levels in animals are not only maintained by heme synthesis, but also by distally located proteins that could signal systemic heme requirements to an inter-organ heme trafficking network through cell-nonautonomous regulation. Using C. elegans, a genetically and optically amenable animal model for visualizing heme-dependent signaling, we show that HRG-7, an aspartic protease homolog, mediates inter-organ signaling between the intestine and neuron. Loss of hrg-7 results in robust expression of intestinal heme importers and, remarkably, this occurs even under heme replete conditions when such transporters are not normally expressed. HRG-7 functions as a secreted signaling factor, independent of a functional enzymatic active site, and communicates intestinal heme status with extraintestinal tissues by integrating a DBL-1/BMP -dependent response from the neurons to transcriptionally regulate intestinal heme homeostasis. Given the evidence indicating that mechanisms of heme transport are conserved across metazoa, it is conceivable that the cell-nonautonomous signaling framework that we uncovered in C. elegans may have functional relevance for inter-organ regulation of iron and heme metabolism in humans.

Project description:The response regulator HrrA belonging to the HrrSA two-component system (previously named CgtSR11) is known to be repressed by the global iron-dependent regulator DtxR in Corynebacterium glutamicum. Sequence analysis indicated an involvement of the HrrSA system in heme-dependent gene expression. Growth experiments revealed that the non-pathogenic soil bacterium C. glutamicum is able to use hemin or hemoglobin as sole iron source. In DNA microarray analyses a putative operon encoding the hemin-binding protein HtaA and the putative hemin ABC transporter HmuTUV showed a strong upregulation in heme-grown cells. Deletion of the hmu operon clearly affects heme utilization, but does not completely abolish growth on heme or hemoglobin. As a central part of this study, we investigated the regulon of the response regulator HrrA via comparative transcriptome analysis of a hrrA deletion mutant and C. glutamicum wild type in combination with DNA-protein interaction studies with purified HrrA protein. Our data provide evidence for a heme-dependent transcriptional activation of heme oxygenase (hmuO), an enzyme involved in the utilization of heme as iron source. Besides hmuO, HrrA was shown to activate the expression of heme-containing components of the respiratory chain, namely ctaD and the ctaE-qcrCAB operon encoding subunits I and III of cytochrome aa3 oxidase and three subunits of the cytochrome bc1 complex. Furthermore, HrrA represses almost all genes involved in heme biosynthesis, including glutamyl-tRNA reductase (hemA), uroporphyrinogen decarboxylase (hemE), and ferrochelatase (hemH). Thus, our data clearly emphasize a central role of the HrrSA system in the control of heme homeostasis in C. glutamicum. Three biological replicates of each experiment were performed. Experiment 1: Transcriptome comparison of wild type grown und FeSO4 or heme as iron source; Exp. 2: WT vs. hrrA deletion mutant grown on FeSO4; Exp. 3: WT vs. hrrA mutant grown on heme. For analysis via DNA microarraysose RNA was isolated from exponentially growing cells cultivated in CgXII medium containing glucose as carbon source and either 2.5 uM FeSO4 or 2.5 uM heme as iron source.

Project description:C. elegans has served as a laboratory model organism due to its ease of manipulation and the availability of both forward and reverse genetics. In recent years, efforts to study host-pathogen interactions in C. elegans have increased. For example, analysis of infections by bacteria such as Pseudomonas, Salmonella or Serratia has revealed the existence of innate immune pathways in C. elegans that are also conserved in vertebrates. To date, there has been no natural virus infection reported in C. elegans or C. briggsae. Here we describe evidence of natural virus infection in wild isolates of both C. elegans and C. briggsae. Two highly divergent but related RNA viruses in the family Nodaviridae, tentatively named Orsay nodavirus and Santeuil nodavirus, were detected and their genomes partially sequenced. Infected worm lysates passed through 0.2 um filters could be used to infect uninfected worms, which could be further passaged for many generations. Furthermore, the viruses were subject to processing by the RNAi machinery as evidenced by the detection of virally derived small RNAs. Infection of mutant worms defective in small RNA pathways yielded more robust levels of viral RNA as compared to infection of isogenic N2 reference worms. These data demonstrate that nodaviruses are natural parasites of nematodes in the wild. Further study of the interactions between these viruses and nematodes is likely to provide insight into the natural ecology of nematodes and may reveal novel innate immune mechanisms that respond to viral infection. Two small RNA libraries (18-30 nt) from nodavirus-infected and cured C. elegans wild isolate JU1580 were sequenced on the Illumina Genome Analyzer II platform. Samples were treated with tobacco acid pyrophosphatase to allow cloning of small RNA molecules with 5'-triphosphates. Each sample was labelled with a unique four base pair barcode and libraries were multiplexed together with a third library (not included in this submission). The multiplexed libraries were sequenced in triplicate.

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Transcription profiling of C. elegans reveals heme homeostasis is regulated by the conserved and concerted functions of HRG-1 proteins

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Haem homeostasis is regulated by the conserved and concerted functions of HRG-1 proteins.

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