The Genomics of Mouse Milk Lipid Synthesis

Mouse milk, like human milk, contains substantial quantities of long chain polyunsaturated fatty acids (LC-PUFA).  The same is not true of cow milk as shown by the following table:

All data expressed as wt%
*On a Western diet with small quantities of fish oils.

The question is whether these fatty acids are synthesized in the mammary gland or are transported from the liver.  Analysis of expression arrays during secretory differentiation and activation suggests that enzymes for elongation and desaturation of fatty acids are present in the mouse mammary gland and that they are turned on at the onset of lactation.  Further, the genes for fatty acid synthesis in general are much higher in the mammary gland than in the liver; e.g. fatty acid synthase is expressed at a level 186 times higher in the mammary gland than the liver and elongation (Evolve 1) and desaturation (FADS 1) genes are expressed at levels three times their levels in the liver. By contrast, many cholesterol synthesis genes are expressed at higher levels in the liver than the mammary gland, suggesting that cholesterol is synthesized in the liver and transported to the mammary gland.  One implication of these observations is that it might be possible to genetically modify the mammary glands of dairy species to secrete higher concentrations of LC-PUFA, which would be advantageous for human diets.  Supported by P01 HD38129 to MCN.