Alpha-mannosidase-II deficiency results in dyserythropoiesis and unveils an alternate pathway in oligosaccharide biosynthesis

Alpha-mannosidase-II (alpha M-II) catalyzes the first committed step in the biosynthesis of complex asparagine-linked (N-linked) oligosaccharides (N-glycans). Genetic deficiency of alpha M-II should abolish complex N-glycan production as reportedly does inhibition of alpha M-II by swainsonine. We find that mice lacking a functional alpha M-II gene develop a dyserythropoietic anemia concurrent with loss of erythrocyte complex N-glycans. Unexpectedly, nonerythroid cell types continued to produce complex N-glycans by an alternate pathway comprising a distinct alpha-mannosidase. These studies reveal cell-type-specific variations in N-linked oligosaccharide biosynthesis and an essential role for alpha M-II in the formation of erythroid complex N-glycans. alpha M-II deficiency elicits a phenotype in mice that correlates with human congenital dyserythropoietic anemia type II.