Comparison of Different RNA Sources to Examine the Lactating Bovine Mammary Gland Transcriptome using RNA-Sequencing

Abstract
The objective of the present study was to examine five different sources of RNA, namely mammary gland tissue (MGT), milk somatic cells (mSC), antibody-captured milk mammary epithelial cells (mMEC), milk fat globules (mFG) and laser microdissected mammary epithelial cells (LCMEC), to analyze the bovine mammary gland transcriptome, using RNA-Sequencing. Given the small amount of materials we started from, especially from mFG, mMEC and LCMEC, the five RNA preparations were amplified, using the Ribo-SPIA technology from the Ovation RNA-seq System (NuGEN, San Carlos, CA). Our results provide an objective assessment between invasive and non-invasive sampling methods to analyze and compare the transcriptome of mammary gland tissue and milk cells. This information is of value to choose the most appropriate sampling method for different research applications, to study specific physiological and health states during lactation. The simplest procedures to study the transcriptome associated with milk appears to be the isolation of total RNA directly from mSC or mFG from milk. Our results indicate that the mSC and mFG transcriptomes are representative of MGT and LCMEC, respectively, and can be used as effective and alternative samples to study mammary gland expression without the need to perform any tissue biopsy.