Differential Expression And Function Of MicroRNA In The Development Of Goat Mammary Gland

The lipid homeostasis of the organism is regulated by a complex regulatory network formed by the multiple signal pathways that consist of genes associated with lipid metabolism.Micro RNAs(miRNAs)act as a post-transcriptional factor that altered expression of genes involved in fat synthesis or fatty acid oxidation,play an important role in regulating the network.In this study,we firstly use S-poly(T)plus q RT-PCR to profile the expression level of miRNAs in the goat mammary gland tissue of different lactation periods.This dynamic expression profile will help us to understand how the miRNAs regulate lipid-related gene.Out of 788 miRNAs,715 were effectively detected and 112 miRNAs are differently expressed at least two-fold in Peak-laction compared to that in the Early-laction.After preliminary screening,20 miRNAs that differently expressed,may participate in regulating lipid metabolism were found and 9 of them have not been reported.6 of 20 miRNAs(let-7c,mi R-19 b,mi R-497,mi R-484,mi R-25 and mi R-17-5p)were selected to further investigate their possible function.Mammary epithelial cells were a common model use for studying milk fat metabolism in vitro.Those 6 miRNAs were over-express in GMECs by using mimic.We found that over-experssion of mi R-25 significantly reduce the intracellular triglyceride content.This result was concerted with the expression trend of mi R-25 in different lactation.Compared to the unpregnant period,the expression of mi R-25 was down-regulated along with the development of mammary gland tissues and lowest at the peak-laction,then up-regulate a little on the late-laction.Next,we predicted that peroxisome proliferator-activated receptor gamma,coactivator 1 beta(PGC-1?)was a potential target of mi R-25,which was confirmed by the 3'UTR luciferase reporter assay and Western blotting analysis.PGC-1? has been shown that was required for full transcriptional activity of Sterol Regulatory Element-binding Protein 1c(SREBP-1c),which was reduced at the same time when overexpress mi R-25.So that mi R-25 may indirectly regulated the expression of SREBP-1c and its target genes involved in lipid metabolism by target PGC-1?.Take together,our study performed an analysis of mi RNA expression profiling of goat mammary gland during the lactation.We propose a model of mi R-25-PGC-1?,perhaps regulate regulated the expression of SREBP-1c to mediated lipid metabolism and our work contributes to further understanding of the functional significance of miRNAs.