Abstract
BackgroundSchistosomiasis japonica remains a major public health problem in China. Its pathogen, Schistosoma japonicum has a complex life cycle and a unique repertoire of genes expressed at different life cycle stages. Exploring schistosome gene regulation will yield the best prospects for new drug targets and vaccine candidates. MicroRNAs (miRNAs) are a highly conserved class of noncoding RNA that control many biological processes by sequence-specific inhibition of gene expression. Although a large number of miRNAs have been identified from plants to mammals, it remains no experimental proof whether schistosome exist miRNAs.Methodology and ResultsWe have identified novel miRNAs from Schistosoma japonicum by cloning and sequencing a small (18–26 nt) RNA cDNA library from the adult worms. Five novel miRNAs were identified from 227 cloned RNA sequences and verified by Northern blot. Alignments of the miRNAs with corresponding family members indicated that four of them belong to a metazoan miRNA family: let-7, miR-71, bantam and miR-125. The fifth potentially new (non conserved) miRNA appears to belong to a previously undescribed family in the genus Schistosome. The novel miRNAs were designated as sja-let-7, sja-miR-71, sja-bantam, sja-miR-125 and sja-miR-new1, respectively. Expression of sja-let-7, sja-miR-71 and sja-bantam were analyzed in six stages of the life cycle, i.e. egg, miracidium, sporocyst, cercaria, schistosomulum, and adult worm, by a modified stem-loop reverse transcribed polymerase chain reaction (RT-PCR) method developed in our laboratory. The expression patterns of these miRNAs were highly stage-specific. In particular, sja-miR-71 and sja-bantam expression reach their peaks in the cercaria stage and then drop quickly to the nadirs in the schistosomulum stage, following penetration of cercaria into a mammalian host.ConclusionsAuthentic miRNAs were identified for the first time in S. japonicum, including a new schistosome family member. The different expression patterns of the novel miRNAs over the life stages of S. japonicum suggest that they may mediate important roles in Schistosome growth and development.
Highlights
Noncoding RNAs of approximately 22 nucleotides in length are becoming increasingly recognized as important regulators of gene expression in animals, plants, and viruses [1]
Authentic miRNAs were identified for the first time in S. japonicum, including a new schistosome family member
RISCbound miRNAs bind to their target mRNA through base pairing with the seed sequence, a section of the miRNA located at the 59 end that includes 2–8 nucleotides, and either cleave the molecule or repress translation, thereby exerting post-transcriptional control of gene expression [2]
Summary
Noncoding RNAs (ncRNAs) of approximately 22 nucleotides (nt) in length are becoming increasingly recognized as important regulators of gene expression in animals, plants, and viruses [1]. One class of these short RNAs, microRNAs (miRNAs), inhibits gene expression through specific base-paring with target mRNAs. Mature miRNAs are produced through two sequential cleavages of longer precursors, which typically contain a stem-loop structure, by the miRNA processing enzymes, Drosha (which acts in the nucleus) and Dicer (which acts in the cytoplasm). A large number of miRNAs have been identified from plants to mammals, it remains no experimental proof whether schistosome exist miRNAs
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