MiR-126-3p regulates progesterone receptors and involves development and lactation of mouse mammary gland.

MicroRNAs (miRNAs) are small (18-22 nucleotide) non-coding, endogenous regulatory RNA molecules, and they regulate gene expression at the post-transcriptional level through binding to their target mRNAs by base-pairing and subsequently inducing either translational repression or mRNA destabilization by plants, animals, and some viruses. In this study, combining microarray techniques with qRT-PCR, we found that miR-126-3p expression showed significant difference in the mouse mammary cycle during pregnancy, particularly on transition from pregnancy to lactation. Bioinformatics were used to predict target gene of miR-126-3p, and luciferase activity assay to test it, it showed that the progesterone receptor (PGR) 3'UTR is directly targeted by miR-126-3p. In this study, mouse mammary epithelial cells as cell model in vitro were used to study the function of miR-126-3p. Using gene silencing and over-expression for miR-126-3p, the expression of PGR protein and the secretion of casein were detected by western blotting and HPLC, respectively. To determine whether miR-126-3p can affect mouse mammary epithelial cells viability, cells were analyzed by CASY-YY. In conclusion, PGR gene confirmed miR-126-3p target genes through luciferase activity and western blotting. And miR-126-3p could also inhibit proliferation of mouse mammary epithelial cells (P < 0.01) and expression of β-casein (P < 0.01), and down-regulate PGR protein (P < 0.05). Our results suggested that miR-126-3p inhibited expression of PGR protein level as well as the proliferation of mammary epithelial cells, therefore miR-126-3p could play an important role in the process of mammary gland development.