The function of lactation: regulation of biosynthesis of the milk components

Abstract

The mammary gland is the organ in which biosynthesis and secretion of milk take place. These processes involve complex molecular mechanisms for which the regulation remains largely unknown. Many studies are being conducted aiming to identify the factors that can modulate the composition of milk to meet the demand of the industry and consumers as well as to identify underlying mechanisms of action and regulation, as precisely as possible. The objective of this paper was to review our current knowledge on the characterisation of genetic and nutritional factors as well as data highlighting the consequences of their interactions on lactation. Two studies on the effects of genetic polymorphisms on the mammary functioning in goats (CSN1S1 locus specifying αS1-casein) and cattle (DGAT1 locus specifying diacylglycerol acyltransferase 1) have allowed highlighting genes involved in lipid metabolism differentially expressed, but also identifying genes involved in vesicular trafficking and "Unfolded Protein Response" in goats. Examples of nutritional regulation of lipid metabolism with inter-species specific regulation (e.g.: differences in the response to lipid supplementation between dairy cows and goats), and examples of the use of holistic approaches allowing the discovery of genes for lipid metabolism, (e.g.: ACSBG1 and AZGP1, specifying respectively lipidosin and zinc-α2-glycoprotein, for which expression in mammary gland has until now remained unknown) or revealing changes in mammary cell dynamics. Finally, interactions between genetic and nutritional factors are presented through a description of regulatory molecular mechanisms of gene expression involving small non coding RNA: microRNA. Taken together, these new data suggest many potentials of research towards more comprehensive and precise understanding of the lactating mammary gland functioning.