Changes in lipid metabolism are essential for terminal erythropoiesis in mice and humans. (A) Photographs of E14.5 WT and PHOSPHO1 KO mice showing impaired growth and pallor of the mutants, highlighting the importance of phosphocholine metabolism in later red cell maturation. (B) Human CD34⁺ cells differentiated using a 5-stage in vitro culture, following which lipid metabolites were extracted and analyzed. Relative amounts of polar metabolites (colored boxes, right) with VIP scores (bottom) indicate loss of phosphocholine and increase in choline toward the end of erythroid differentiation. VIP, variable importance in projection; WT, wild-type. See Figures 2B and 6A in the article by Huang et al that begins on page 2955.