In mammals, the only endogenous pathway for choline biosynthesis is the methylation of
phosphatidylethanolamine to phosphatidylcholine (PC) by phosphatidylethanolamine N-
methyltransferase (PEMT) coupled to PC degradation. Complete choline deprivation in mice
by feeding Pemt-/-mice a choline-deficient (CD) diet decreases hepatic PC by 50% and is
lethal within 5 days. PC secretion into bile is mediated by a PC-specific flippase, multiple
drug-resistant protein 2 (MDR2). Here, we report that mice that lack both PEMT and MDR2 …