Mammary Epithelial Cell Transcriptome Reveals Potential Roles of lncRNAs in Regulating Milk Synthesis Pathways in Jersey and Kashmiri Cattle

Background Long noncoding RNAs (lncRNAs) are now proven as essential regulatory elements, playing diverse role in many biological processes including mammary gland development. However, little is known about their roles in bovine lactation process. There are very few reports available to date on the role of lncRNAs in lactation physiology and mammary glands development in cattle. Results To identify and characterize the roles of lncRNAs in bovine lactation, milk derived mammary epithelial cells (MEC) from Jersey (high milk producer) and Kashmiri cattle (low milk producer) at early, mid and late lactation stages were used. The lncRNA transcriptome of the samples (n=18) was studied using next generation RNA sequencing technology. 633 putative lncRNAs were identified, 76 of which were differentially expressed (DE) between comparison between the three stages of lactation. Additionally, 56 DE lncRNAs were identified from 9 Jersey and 9 Kashmir samples. Correlation of DE lncRNAs with protein-coding genes resulted in a comprehensive list of lncRNA-mRNA co-expressed pairs. Most of the DE lncRNAs showed positive correlations with protein coding genes in Jersey compared to Kashmiri cattle where they were mainly negatively correlated, which could be one of the underlying mechanisms responsible for the differential milking performance between the two breeds. In addition, a number of the DE lncRNAs were paired with the most DE milk quality genes like GPAM, LPL, ABCG2, etc. indicative of their potential regulatory effects on milk quality genes. KEGG pathways analysis of potential cis and trans target genes of DE lncRNAs indicated that 27 and 48 pathways were significantly enriched in Kashmiri and Jersey respectively, including mTOR signaling, PI3K-Akt signaling and RAP1 signaling pathways. These pathways have been proven to play key roles in lactation biology and mammary gland development. Conclusions Our study mapped the expression profiles of lncRNAs across lactation stages and their relationships with candidate genes related to milk quality and yield traits in Jersey and Kashmiri cattle. These findings provide a valuable resource for the study of the regulatory mechanisms involved in the lactation process as well as facilitate understanding of the role of lncRNAs in bovine lactation biology.