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Since 2015, the dairy sector has to reorganize to go on producing in absence of quotas and new challenges appear. Indeed, the world demand for milk and dairy products increases year by year, in particular in China. In addition, this sector has to compose with the societal expectations on the environmental impact related to the cattle farm (breeding). In this context, Research on the lactation of the dairy cow and in particular on the mammary gland function seems as an important lever in the understanding on the animal adaptation to these new practices of breeding.

Understand the plasticity of the mammary gland from the cells which compose it

Milk in dairy cows is produced by the mammary gland, a complex and dynamic organ composed of several cellular types integrated into an extracellular matrix micro-environment. The milk is secreted by the epithelial cells within the alveoli of the mammary gland. In the epithelial populations, we distinguish the luminal cells which synthesize the constituents of milk, of the basal cells located at the galactophores ducts and the myoepithelial cells in border of acini responsible for the ejection of secreted milk. Epithelial cells are lined by others populations: the fibroblasts which connect cells within the tissue by producing the extracellular matrix, the adipocytes storing energy and the endothelial cells lining the blood vessels which provide nutrients to mammary gland. All together, these populations participate in production of milk.

The proliferative and regenerative capacities of the mammary tissue during the reproductive cycles and lactation make of the mammary gland a unique organ enable to renew 50% of its cells during one lactation (Capuco et al., 2001). Stem cells are found in the mammary epithelium, these cells able to self-renewal largely contribute to the plasticity of the gland during the reproductive cycles (pregnancy, lactation, and involution). It was established that the epithelial stem cells were able to differentiate in progenitor cells, committed in a differentiation pathway but retaining substantial proliferation capacity, and that these cells gave rise to differentiated epithelial cells responsible for milk synthesis (Capuco et al., 2012).
The role of adult mammary stem cells and progenitor cells has been studied extensively in murine and human models. However, the fate and plasticity of these cells during a lactation cycle are not yet characterized in dairy cows. Thus, the lineage and the functional characterization of mammary epithelial populations, from the stem cells to differentiated cells would establish precisely the phenotype of the mammary gland in accordance with a particular physiological stage.

The objectives of this thesis

• identify specific surface markers of the different cell types present in the mammary gland
• isolate and characterize in vitro these different cell types from mammary explants
• study their potential for differentiation / dedifferentiation / transdifferentiation in vitro

The purpose of this project is to identify markers of mammary stem cells to predict and detect the future dairy potential. This project will thus provide data for our understanding of stem cell function in ruminants and will contribute to develop biomarkers to  improve  mammogenesis and milk production.

Laurence Finot, laboratory tecnician at Pegase has been working on this subject of thesis since September 2015 for 3 years. She is supervised by Frédéric Dessauge in the lactation team.

Bibliographie

• Capuco AV, Wood DL, Baldwin R, McLeod K and Paape MJ 2001. Mammary cell number, proliferation, and apoptosis during bovine lactation: relation to milk production and effect of bST. Journal of Dairy Science 84, 2177-2187. (DOI)
• Capuco AV, Choudhary RK, Daniels KM, Li RW and Evock-Clover CM 2012. Bovine mammary stem cells: cell biology meets production agriculture. Animal 6:3, 382-393. (DOI)

Contact

Laurence Finot, laurence.finot[at]rennes.inra.fr (doctorante)
Frédéric Dessauge, frederic.dessauge[at]rennes.inra.fr (encadrant)