Identification and comparison of microRNAs in pituitary gland during prenatal and postnatal stages of sheep by deep sequencing.

MicroRNAs (miRNAs) are a class of short-chain RNA molecules of ~22 nucleotides in length and regulate gene expression at posttranscriptional levels by interacting with mRNAs. Although many miRNAs have been identified, the expression and function of miRNAs in the pituitary gland of sheep are still unclear. In this study, the identity and abundance of miRNAs were determined in the sheep pituitary gland of prenatal and postnatal stages. We showed that 107 miRNAs are significantly (P<0.05) differentially expressed in pituitary glands between the prenatal and postnatal stages, and 44 new miRNA candidates were found according to a series of filtration criteria. Reverse-transcription polymerase chain reaction (RT-PCR) and DNA sequencing analysis confirmed the presence of several miRNAs. Real-time RT-PCR analysis showed that sheep miRNAs were expressed in prenatal and postnatal pituitary glands. We found that miRNAs were involved in hormone synthesis, secretion and signalling pathway regulation by gene ontology (GO) and KEGG concentration analysis. Our study provides valuable resources for comprehensive investigation of miRNAs in the pituitary gland and biology of sheep.