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DEVELOPING

Two tissue-specific promoters drive Pklr, the mouse ortholog of human PKLR, producing the liver and erythrocyte pyruvate kinase isozymes that catalyze the final, effectively irreversible step of glycolysis, transferring phosphate from phosphoenolpyruvate to ADP under strong allosteric activation by fructose 1,6-bisphosphate and inhibition by ATP and alanine, with the hepatic form additionally suppressed by glucagon-driven phosphorylation. Recessive loss-of-function alleles cause pyruvate kinase deficiency, the commonest enzymatic cause of hereditary nonspherocytic hemolytic anemia, in which ATP depletion in mature erythrocytes that lack mitochondria drives membrane failure and 2,3-bisphosphoglycerate accumulation. Design follows the tissue split: patient-matched missense knockins reproduce the unstable, allosterically impaired enzyme and are the correct substrate for testing activators of the mitapivat class, while conditional nulls separate hepatic from erythroid consequences. The paralogous Pkm locus serves other tissues but does not rescue red cells. Match allele class to hematologic or hepatic glucose endpoints.

Whole body loss of Pklr gives the clearest readout when the question is whether the gene is required at all. Follow up tissue work can still move to a conditional allele if lethality or compensation appears.