Rescue of embryonic lethality in reduced folate carrier-deficient mice by maternal folic acid supplementation reveals early neonatal failure of hematopoietic organs

The reduced folate carrier (RFC1) is an important route by which the major blood folate, B-methyltetrahydrofolate, is transported into mammalian cells . In this study we determined the consequences of inactivation of RFC1 in m ice by homologous recombination. While RFC1-null embryos died in utero befo re embryonic day 9.5 (E9.5), near-normal development could be sustained in RFC1(-/-) embryos examined at E18.5 by supplementation of pregnant RFC1(+/- ) darns with l-mg daily subcutaneous doses of folic acid. About 10% of thes e animals went on to live birth but died within 12 days. These RFC1(-/-) mi ce showed a marked absence of erythropoiesis in bone marrow, spleen, and li ver along with lymphoid depletion in the splenic white pulp and thymus, In addition, there was some impairment of renal and seminiferous tubule develo pment. These data indicate that in the absence of RFC1 function, neonatal a nimals die due to failure of hematopoietic organs.