MicroRNAs (miRNAs) are small noncoding RNAs present in milk-derived extracellular vesicles and milk fat globules (MFG). Nucleic acid content between the lactating mammary tissue (MT) and MFG are quite similar but discrepancies exist in their miRNA content. Our objective was to identify the origin of these discrepancies, and to evaluate the existence of a possible mechanism sorting miRNAs that will or will not be exported from the mammary epithelial cells (MECs) in bovine MFG. miR-125b-5p, miR-126-3p, miR-141-3p, and miR-204-5p, chosen on the basis of their abundance in the MT, were quantified using RT-qPCR in lactating cow MT, MFG, and laser capture-microdissected MECs. Two miRNAs (miR-125b-5p and miR-141-3p) were detected in the MT as well as in MFG and MECs. miR-204-5p was detected only in the MT, suggesting that it is very likely expressed in a cell type other than MECs. miR-126-3p was detected both in the MT and in MECs but not in MFG, suggesting a targeting mechanism for miRNAs in MECs. These results highlights differences in miRNA content between MECs and MFG may be due to a possibly not random mechanism for loading MFG with miRNA cargos that could involve a variable distribution in MECs or a sorting mechanism.

微小RNA（miRNA）是存在于牛奶来源的细胞外小泡和牛奶脂肪小球（MFG）中的小型非编码RNA。哺乳期乳腺组织（MT）和MFG之间的核酸含量非常相似，但其miRNA含量存在差异。我们的目标是确定这些差异的起源，并评估可能存在的机制，该机制对从牛MFG的乳腺上皮细胞（MEC）输出或不输出的miRNA进行分类。根据其在MT中的丰度选择的miR-125b-5p，miR-126-3p，miR-141-3p和miR-204-5p在乳牛MT，MFG和激光捕获显微切割的MEC。两个miRNA（miR-125b-5p和在MT以及MFG和MEC中检测到miR-141-3p）。miR-204-5p仅在MT中检测到，表明它很可能在MEC以外的细胞类型中表达。在MT和MEC中均检测到miR-126-3p，但在MFG中均未检测到，这表明MEC中miRNA的靶向机制。这些结果表明，MEC和MFG之间miRNA含量的差异可能是由于可能不是随机的机制来装载MFG的miRNA货物，而这可能涉及到MEC中的可变分布或分选机制。