Differential Expression of MicroRNAs in the Mammary Gland of Lactating and Dry Murciano-Granadina Goats

In goats, the influence of microRNAs on the post-transcriptional regulation of genes involved in mammary development and remodeling and milk secretion has not been fully elucidated yet. In this study, we have obtained mammary biopsies from five lactating and four dry Murciano-Granadina goats and, subsequently, small RNA has been purified and sequenced, obtaining, on average, 11 million reads per sample with an 85% alignment rate. Bioinformatic analysis of the sequencing data revealed the expression of 342 unique microRNAs in the goat mammary gland, among which 32 were novel miRNAs. Moreover, we have determined that as many as 93 mature microRNAs are differentially expressed (fold-change ≥ 2.7, q-value = 0.05) in lactating vs. dry goats. Of these, 49 and 44 were upregulated and downregulated in lactating goats, respectively, including 13 novel miRNAs. For each one of these differentially expressed miRNAs, we have made a search of scientific literature to find out whether their functional role in lactation has been elucidated, and, if so, we have contrasted the expected (based on function) vs. the observed (inferred from the differential expression analysis) change in gene expression to determine their degree of concordance. About 82% of the miRNAs with functional information that were differentially expressed in lactating vs. dry goats showed concordance between the observed and expected directions of the change in gene expression. By integrating differential expression analysis and functional data generated by others, we have identified a set of 17 miRNAs with converging evidence of being involved in the physiological transformations associated with lactation and mammary involution.