LAUSR

MicroRNAs (miRNAs) are noncoding RNA molecules that regulate gene expression at the post‐transcriptional level to cause translational repression or degradation of targets. The profiles of miRNAs across stages of lactation in small ruminant species such as dairy goats is unknown. A small RNA library was constructed using tissue samples from mammary gland of Saanen dairy goats harvested at mid‐lactation followed by sequencing via Solexa technology. A total of 796 conserved miRNAs, 263 new miRNAs, and 821 pre‐miRNAs were uncovered. After comparative analyses of our sequence data with published mammary gland transcriptome data across different stages of lactation, a total of 37 miRNAs (including miR‐145) had significant differences in expression over the lactation cycle. Further studies revealed that miR‐145 regulates metabolism of fatty acids in goat mammary gland epithelial cells (GMEC). Compared with nonlactating mammary tissue, lactating mammary gland had a marked increase in expression of miR‐145. Overexpression of miR‐145 increased transcription of genes associated with milk fat synthesis resulting in greater fat droplet formation, triacylglycerol accumulation, and proportion of unsaturated fatty acids. In contrast, silencing of miR‐145 impaired fatty acid synthesis. Inhibition of miR‐145 increased methylation levels of fatty acid synthase (FASN), stearoyl‐CoA desaturase 1 (SCD1), peroxisome proliferator‐activated receptor gamma (PPARG), and sterol regulatory element binding transcription factor 1 (SREBF1). Luciferase reporter assays confirmed that insulin induced gene 1 (INSIG1) is a direct target of miR‐145. These findings underscore the need for further studies to evaluate the potential for targeting miR‐145 for improving beneficial milk components in ruminant milk. J. Cell. Physiol. 232: 1030–1040, 2017. © 2016 Wiley Periodicals, Inc.