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RNA interference targeting leucine aminopeptidase blocks hatching of Schistosoma mansoni eggs.

ABSTRACT: Schistosoma mansoni leucine aminopeptidase (LAP) is thought to play a central role in hatching of the miracidium from the schistosome egg. We identified two discrete LAPs genes in the S. mansoni genome, and their orthologs in S. japonicum. The similarities in sequence and exon/intron structure of the two genes, LAP1 and LAP2, suggest that they arose by gene duplication and that this occurred before separation of the mansoni and japonicum lineages. The SmLAP1 and SmLAP2 genes have different expression patterns in diverse stages of the cycle; whereas both are equally expressed in the blood dwelling stages (schistosomules and adult), SmLAP2 expression was higher in free living larval (miracidia) and in parasitic intra-snail (sporocysts) stages. We investigated the role of each enzyme in hatching of schistosome eggs and the early stages of schistosome development by RNA interference (RNAi). Using RNAi, we observed marked and specific reduction of mRNAs, along with a loss of exopeptidase activity in soluble parasite extracts against the diagnostic substrate l-leucine-7-amido-4-methylcoumarin hydroxide. Strikingly, knockdown of either SmLAP1 or SmLAP2, or both together, was accompanied by >or=80% inhibition of hatching of schistosome eggs showing that both enzymes are important to the escape of miracidia from the egg. The methods employed here refine the utility of RNAi for functional genomics studies in helminth parasites and confirm these can be used to identify potential drug targets, in this case schistosome aminopeptidases.

SUBMITTER: Rinaldi G

PROVIDER: S-EPMC2705689 | biostudies-literature | 2009 Oct

REPOSITORIES: biostudies-literature

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RNA interference targeting leucine aminopeptidase blocks hatching of Schistosoma mansoni eggs.

Rinaldi Gabriel G Morales Maria E ME Alrefaei Yousef N YN Cancela Martín M Castillo Estela E Dalton John P JP Tort José F JF Brindley Paul J PJ

Molecular and biochemical parasitology 20090520 2

Schistosoma mansoni leucine aminopeptidase (LAP) is thought to play a central role in hatching of the miracidium from the schistosome egg. We identified two discrete LAPs genes in the S. mansoni genome, and their orthologs in S. japonicum. The similarities in sequence and exon/intron structure of the two genes, LAP1 and LAP2, suggest that they arose by gene duplication and that this occurred before separation of the mansoni and japonicum lineages. The SmLAP1 and SmLAP2 genes have different expre ...[more]

PMID: 19463860

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Project description:BACKGROUND: The possible emergence of resistance to the only available drug for schistosomiasis spurs drug discovery that has been recently incentivized by the availability of improved transcriptome and genome sequence information. Transient RNAi has emerged as a straightforward and important technique to interrogate that information through decreased or loss of gene function and identify potential drug targets. To date, RNAi studies in schistosome stages infecting humans have focused on single (or up to 3) genes of interest. Therefore, in the context of standardizing larger RNAi screens, data are limited on the extent of possible off-targeting effects, gene-to-gene variability in RNAi efficiency and the operational capabilities and limits of RNAi. METHODOLOGY/PRINCIPAL FINDINGS: We investigated in vitro the sensitivity and selectivity of RNAi using double-stranded (ds)RNA (approximately 500 bp) designed to target 11 Schistosoma mansoni genes that are expressed in different tissues; the gut, tegument and otherwise. Among the genes investigated were 5 that had been previously predicted to be essential for parasite survival. We employed mechanically transformed schistosomula that are relevant to parasitism in humans, amenable to screen automation and easier to obtain in greater numbers than adult parasites. The operational parameters investigated included defined culture media for optimal parasite maintenance, transfection strategy, time- and dose-dependency of RNAi, and dosing limits. Of 7 defined culture media tested, Basch Medium 169 was optimal for parasite maintenance. RNAi was best achieved by co-incubating parasites and dsRNA (standardized to 30 µg/ml for 6 days); electroporation provided no added benefit. RNAi, including interference of more than one transcript, was selective to the gene target(s) within the pools of transcripts representative of each tissue. Concentrations of dsRNA above 90 µg/ml were directly toxic. RNAi efficiency was transcript-dependent (from 40 to >75% knockdown relative to controls) and this may have contributed to the lack of obvious phenotypes observed, even after prolonged incubations of 3 weeks. Within minutes of their mechanical preparation from cercariae, schistosomula accumulated fluorescent macromolecules in the gut indicating that the gut is an important route through which RNAi is expedited in the developing parasite. CONCLUSIONS: Transient RNAi operates gene-selectively in S. mansoni newly transformed schistosomula yet the sensitivity of individual gene targets varies. These findings and the operational parameters defined will facilitate larger RNAi screens.

Project description:RNA interference (RNAi) represents the only method currently available for manipulating gene-specific expression in Schistosoma spp., although application of this technology as a functional genomic profiling tool has yet to be explored. In the present study 32 genes, including antioxidants, transcription factors, cell signaling molecules and metabolic enzymes, were selected to determine if gene knockdown by RNAi was associated with morphologically definable phenotypic changes in early intramolluscan larval development. Transcript selection was based on their high expression in in vitro cultured S. mansoni primary sporocysts and/or their potential involvement in developmental processes. Miracidia were allowed to transform to sporocysts in the presence of synthesized double-stranded RNAs (dsRNAs) and cultivated for 7 days, during which time developing larvae were closely observed for phenotypic changes including failure/delay in transformation, loss of motility, altered growth and death. Of the phenotypes evaluated, only one was consistently detected; namely a reduction in sporocyst size based on length measurements. The size-reducing phenotype was observed in 11 of the 33 (33%) dsRNA treatment groups, and of these 11 phenotype-associated genes (superoxide dismutase, Smad1, RHO2, Smad2, Cav2A, ring box, GST26, calcineurin B, Smad4, lactate dehydrogenase and EF1alpha), only 6 demonstrated a significant and consistent knockdown of specific transcript expression. Unexpectedly one phenotype-linked gene, superoxide dismutase (SOD), was highly induced ( approximately 1600-fold) upon dsRNA exposure. Variation in dsRNA-mediated silencing effects also was evident in the group of sporocysts that lacked any definable phenotype. Out of 22 nonphenotype-expressing dsRNA treatments (myosin, PKCB, HEXBP, calcium channel, Sma2, RHO1, PKC receptor, DHHC, PepcK, calreticulin, calpain, Smeg, 14.3.3, K5, SPO1, SmZF1, fibrillarin, GST28, GPx, TPx1, TPx2 and TPx2/TPx1), 12 were assessed for the transcript levels. Of those, 6 genes exhibited consistent reductions in steady-state transcript levels, while expression level for the rest remained unchanged. Results demonstrate that the efficacy of dsRNA-treatment in producing consistent phenotypic changes and/or altered gene expression levels in S. mansoni sporocysts is highly dependent on the selected gene (or the specific dsRNA sequence used) and the timing of evaluation after treatment. Although RNAi holds great promise as a functional genomics tool for larval schistosomes, our finding of potential off-target or nonspecific effects of some dsRNA treatments and variable efficiencies in specific gene knockdown indicate a critical need for gene-specific testing and optimization as an essential part of experimental design, execution and data interpretation.

Project description:Protein variation in blood-dwelling schistosome worms generated by differential splicing of micro-exon gene transcripts. The infective schistosome cercaria develops from an undifferentiated germ ball within the daughter sporocyst in the molluscan host, during which considerable morphological development and synthesis of proteins essential for infection occurs. The free-living, non-feeding cercaria is notable for its swimming and host location behaviour. On contact with host skin it rapidly penetrates, replaces its tegument surface membranes, and begins body remodelling, before crossing the dermis to exit the skin via a blood vessel. Such a ‘violent’ transition from snail to fresh water to mammalian host should be accompanied by remarkable changes in the patterns of gene expression. All gene models from version E of the S. mansoni genome (www.GeneDB.org) were incorporated into a 350K feature Roche-NimbleGen, high-density oligonucleotide array. From a map-ordered list, every 13th 50mer was chosen as a probe. Double-stranded cDNA from three biological replicates each of germ balls, cercariae, and day 3 schistosomula was hybridised to the array without amplification. Statistical analysis was carried out using programmes from the Bioconductor suite (Gentleman et al. 2004 Genome Biol 5(10):R80). More than 1000 loci were shown to be differentially expressed in each of the comparisons between the three life cycle stages. Gene ontology (GO) analysis was then carried out to discover the categories enriched in each stage. In addition custom categories based on biological function (e.g. stress response) or parasite tissue (e.g. tegument) were analysed. Three biological replicates each of germ balls, cercariae, day 3 in vitro cultured schistosomula, and eggs were used. No technical replicates were included. This is the first genome-wide microarray platform for S. mansoni. It was used to investigate the gene expression patterns of the above lifecycle stages. The first three are the stages before, during and after penetration of mammalian host skin.

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RNA interference targeting leucine aminopeptidase blocks hatching of Schistosoma mansoni eggs.

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RNA interference targeting leucine aminopeptidase blocks hatching of Schistosoma mansoni eggs.

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