Abstract
MicroRNAs are small, noncoding RNA molecules that regulate gene expression at the post-transcriptional level and play an important role in various biological processes. Although most microRNAs expression profiles studies have been performed in humans or rodents, relatively limited knowledge also exists in other mammalian species. The identification of the full repertoire of microRNAs expressed in the lactating mammary gland of Capra hircus would significantly increase our understanding of the physiology of lactating mammary glands. In this study, two libraries were constructed using the lactating mammary gland tissues of Laoshan dairy goats (Capra hircus) during peak and late lactation. Solexa high-throughput sequencing technique and bioinformatics were used to determine the abundance and differential expression of the microRNAs between peak and late lactation. As a result, 19,044,002 and 7,385,833 clean reads were obtained, respectively, and 1,113 conserved known microRNAs and 31 potential novel microRNA candidates were identified. A total of 697 conserved microRNAs were significantly differentially expressed with a P-value<0.01, 272 microRNAs were up-regulated and 425 microRNAs were down-regulated during peak lactation. The results were validated using real-time quantitative RT-PCR. 762,557 annotated mRNA transcripts were predicted as putative target gene candidates. The GO annotation and KEGG pathway analysis suggested that differentially expressed microRNAs were involved in mammary gland physiology, including signal transduction, and cell-cell and cell-extracellular communications. This study provided the first global of the microRNA in Capra hircus and expanded the repertoire of microRNAs. Our results have great significance and value for the elucidation of complex regulatory networks between microRNAs and mRNAs and for the study of mammary gland physiology and lactation.
Highlights
MicroRNAs represent a class of small (,22 nucleotides in length), endogenous, noncoding functional RNA molecules, which generally exist in eukaryotes and have spatiotemporal and tissue-specific expression patterns [1,2]
The lengths of the majority of small RNAs were 19,24 nt, and the most abundant size class in the small RNA sequences distribution was 22 nt, which accounted for 41.48% and 33.96% in peak and late lactation respectively, followed by 20 nt (12.31%, 23.96%), 23 nt (19.32%, 12.53%) and 21 nt (9.91%, 9.96%), which are typical of small RNA Dicer-processed products and are consistent with the known 18,25 nt range for miRNAs
Solexa high-throughput sequencing provided a strong platform for the study of small RNAs in dairy goat mammary gland physiology and lactation
Summary
MicroRNAs (miRNAs) represent a class of small (,22 nucleotides (nt) in length), endogenous, noncoding functional RNA molecules, which generally exist in eukaryotes and have spatiotemporal and tissue-specific expression patterns [1,2]. Tanaka et al [10] revealed that some miRNAs exhibit changes in their expression during mouse mammary gland epithelial cell differentiation. These authors observed that miRNA-101a plays important roles in mouse mammary development. The majority of the reported miRNA research has been focused on disease-related studies in either human or rodents, while the importance of miRNAs in other mammals need further be elucidated, and the essential roles of miRNAs in terms of posttranscriptional gene regulation in lactating mammary gland physiology and lactation of Capra hircus currently remains largely unknown
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