Abstract
BackgroundNon-coding small RNAs, ranging from 20 to 30 nucleotides in length, mediate the regulation of gene expression and play important roles in many biological processes. One class of small RNAs, microRNAs (miRNAs), are highly conserved across taxa and mediate the regulation of the chromatin state and the post-transcriptional regulation of messenger RNA (mRNA). Another class of small RNAs is the Piwi-interacting RNAs, which play important roles in the silencing of transposons and other functional genes. Although the biological functions of the different small RNAs have been elucidated in several laboratory animals, little is known regarding naturally occurring variation in small RNA transcriptomes among closely related species.ResultsWe employed next-generation sequencing technology to compare the expression profiles of brain small RNAs between sympatric species of the Japanese threespine stickleback (Gasterosteus aculeatus). We identified several small RNAs that were differentially expressed between sympatric Pacific Ocean and Japan Sea sticklebacks. Potential targets of several small RNAs were identified as repetitive sequences. Female-biased miRNA expression from the old X chromosome was also observed, and it was attributed to the degeneration of the Y chromosome.ConclusionsOur results suggest that expression patterns of small RNA can differ between incipient species and may be a potential mechanism underlying differential mRNA expression and transposon activity.
Highlights
Non-coding small RNAs, ranging from 20 to 30 nucleotides in length, mediate the regulation of gene expression and play important roles in many biological processes
A miRNA interacts with ten to hundreds of target messenger RNA (mRNA) to induce degradation or suppress translation [12]. Another function of miRNA is epigenetic modification of genomic DNA: miRNAs interact with target DNAs to alter the chromatin state and suppress mRNA transcription [14]. miRNAs comprise more than 1% of animal genes [15,16], suggesting that they play important roles in many biological processes
1300 isoforms of miRNA were detected in the brain (924 in the Pacific Ocean males, 924 in the Pacific Ocean females, 916 in the Japan Sea males, and 884 in the Japan Sea females). miRNA expression profiles demonstrated that miRNAs homologous to mir21, mir100, let7, mir101, mir143, and mir9 were the most abundant in the stickleback brain, regardless of the species or sex (Figure 2)
Summary
Non-coding small RNAs, ranging from 20 to 30 nucleotides in length, mediate the regulation of gene expression and play important roles in many biological processes. One class of small RNAs, microRNAs (miRNAs), are highly conserved across taxa and mediate the regulation of the chromatin state and the post-transcriptional regulation of messenger RNA (mRNA). Another class of small RNAs is the Piwi-interacting RNAs, which play important roles in the silencing of transposons and other functional genes. The biological functions of the different small RNAs have been elucidated in several laboratory animals, little is known regarding naturally occurring variation in small RNA transcriptomes among closely related species. Recent functional studies in laboratory model animals such as mice, flies, and nematodes have demonstrated that miRNAs are important for regulating development, growth, pathogen resistance, and neural functions [11,12,17,18,19]
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