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A non-invasive source of mammary RNA to study physiological mechanisms

In the mammary tissue, transcriptomic regulations drive the process of lactation (Bionaz et al., 2012). However, studying transcriptomic regulations responsible for changes in milk production entails the collection of mammary epithelial cells (MEC). Thus, MEC must be harvested from the mammary gland. The standard method is the collection of mammary tissue by biopsy. However, this requires the performance of a surgical procedure that does not allow easy and repetitive sampling without damaging the mammary tissue. From an ethical point of view, but also based on scientific considerations, it is important to find alternative procedures to surgical ones whenever possible, also avoiding the carry-over effect of sampling that may be observed in mammary biopsies. Previous studies show that milk contains viable MEC (Boutinaud and Jammes, 2002). We developed an immunomagnetic method that enables the isolation of MEC from milk (Boutinaud et al., 2008). We synthesized all the results obtained in our laboratory and by other teams to determine precisely the scope of our method and its limitations.

We showed that transcripts variations in milk-isolated MEC following the application of different treatments and/or rearing practices (such as once-daily milking, feed restriction, advanced lactation, and prolactin inhibition) were similar between several studies in different species (cow, goat and zebu especially). Moreover, the transcript variations in milk-isolated MEC were consistent with milk yield and composition variations. Finally, the variation of several genes involved in milk synthesis under the effect of one factor (once-daily milking) were similarly observed in milk isolated MEC and mammary tissue sampled by biopsy. All these results show the relevance of using milk-isolated MEC method to analyze mammary gene expression However, the RNA from milk-isolated MEC is particularly sensitive to degradation due to the exfoliated nature of these cells. Thus, when the RNA quality is conserved, MEC isolated from milk are a valuable, non-invasive source of mammary mRNA to study the physiological mechanisms by which rearing factors (once-daily milking, feeding level, endocrine status, photoperiod modulation and stage of lactation) modulate the production and composition of milk.

The rate of exfoliation, a major factor that regulates milk production?

The method of cell isolation would provide a promising opportunity to further understand the involvement of microRNA in the lactation process and, also the regulation of mammary host defense. Other non-invasive methods of obtaining mammary RNA have been developed such as the analysis of RNA from milk fat (Brenaut et al., 2012). Nevertheless, the approach by MEC purification from milk has the advantage of also allowing determining the rate of MEC exfoliation from the mammary tissue. The rate of exfoliation would be an indicator of the evolution of MEC number in the mammary gland, which is, with the synthesis activity of MEC, a major factor regulating milk production (Herve et al. 2015).

=> Boutinaud M, L. Herve, V. Lollivier 2015. Mammary epithelial cells isolated from milk are a valuable non-invasive source of mammary transcripts. Front.Genet.6:323. [DOI]

Journal classified in the 1^st quartile from SCImago (Scopus/Elsevier).

Bibliography

• Bionaz, M., Periasamy, K., Rodriguez-Zas, S.L., Hurley, W.L., Loor, J.J. (2012). A novel dynamic impact approach (dia) for functional analysis of time-course omics studies: validation using the bovine mammary transcriptome. PLoS One 7(3), e32455. [DOI]
• Brenaut, P., Bangera, R., Bevilacqua, C., Rebours, E., Cebo, C., Martin, P. (2012). Validation of RNA isolated from milk fat globules to profile mammary epithelial cell expression during lactation and transcriptional response to a bacterial infection. J. Dairy Sci. 95(10), 6130–6144. [DOI]
• Boutinaud, M, Jammes, H. (2002). Potential uses of milk epithelial cells : a review. Reprod. Nutr. Dev. 42(2), 133-47. [DOI]
• Boutinaud, M., Ben Chedly, M.H., Delamaire, E., Guinard-Flament, J. (2008). Milking and feed restriction regulate transcripts of mammary epithelial cells purified from milk. J. Dairy Sci. 91(3), 988-98. [DOI]
• Herve, L., Quesnel, H., Lollivier, V., Boutinaud M. (2016). Regulation of cell number in the mammary gland by controlling the exfoliation process in milk in ruminants. J Dairy Sci. 99 (1), 854-863. [DOI]