Rescue of Embryonic Lethality in Reduced Folate Carrier-deficient Mice by Maternal Folic Acid Supplementation Reveals Early Neonatal Failure of Hematopoietic Organs

Abstract

The reduced folate carrier (RFC1) is an important route by which the major blood folate, 5-methyltetrahydrofolate, is transported into mammalian cells. In this study we determined the consequences of inactivation of RFC1 in mice by homologous recombination. While RFC1-null embryos died in utero before embryonic day 9.5 (E9.5), near-normal development could be sustained in RFC1؊/؊ embryos examined at E18.5 by supplementation of pregnant RFC1؉/؊ dams with 1-mg daily subcutaneous doses of folic acid. About 10% of these animals went on to live birth but died within 12 days. These RFC1 ؊/؊ mice showed a marked absence of erythropoiesis in bone marrow, spleen, and liver along with lymphoid depletion in the splenic white pulp and thymus. In addition, there was some impairment of renal and seminiferous tubule development. These data indicate that in the absence of RFC1 function, neonatal animals die due to failure of hematopoietic organs.

Preservation of folate transport activity with a low-pH optimum in rat IEC-6 intestinal epithelial cell lines that lack reduced folate carrier function

“…However, homozygous deletion of the RFC gene in the mouse is embryonic lethal, and while some RFC Ϫ/Ϫ mice can be brought to term and live up to 12 days when the pregnant (or later, lactating) female is administered high doses of folic acid subcutaneously, these animals die as a result of severe atrophy of hematopoietic tissues (39). There is, however, essentially no intestinal pathology, suggesting the presence of an RFC-independent transport pathway in this tissue (39). The intestine of these pups is too small to permit acquisition of absorptive cells for transport studies.…”

Folate modulates Hox gene‐controlled skeletal phenotypes

“…Indeed, the controls provide no indication that maternal metabolism is deficient in our experimental system: non-transgenic embryos, which are raised together with the Hoxd4 transgenics in the same uterine environment (see Figure 1), lack any discernable developmental defects. Systemic depletion of folate transport to the developing embryo has been achieved genetically by targeted disruption of Folbp1 (Piedrahita et al, 1999) and of Rfc1 (Zhao et al, 2001). Both deficiencies cause early embryonic death and are uninformative for skeletal development; tissue-specific deletion strategies will be needed to clarify the relevance of these transport mechanisms in cartilage formation.…”

A mouse model of hereditary folate malabsorption: deletion of the PCFT gene leads to systemic folate deficiency

“…Targeted disruption of the other folate transporters, RFC1 and FOLR1, results in embryonic lethality in mice. 5,10 Inactivation of the methionine synthase gene (MS), a B12-dependent enzyme required for demethylation of 5-MTHF to tetrahydrofolate, would be expected to produce a functional folate deficiency by trapping folate as 5-MTHF. However, MS deletion leads to embryonic lethality because of the methyl trap, whereas heterozygous MS ϩ/Ϫ mice fail to develop anemia.…”

“…6 Inactivation of RFC1 in mice by homologous recombination led to either embryonic lethality or defective erythropoiesis in pups born to mothers who were supplemented with 1 mg daily subcutaneous doses of folic acid. 10,11 Because this transporter functions at a neutral pH optimum whereas the majority of intestinal folate transport occurs in an acidic luminal milieu, RFC1 is an unlikely candidate for an intestinal folate transporter. 7 The role of FOLR1 in folate absorption and transport has also been demonstrated, where a 60% to 70% reduction was observed in plasma folate of FOLR1 Ϫ/Ϫ mice fed low folate and normal chow.…”