Folate is an essential micronutrient and serves as an enzymatic cofactor in single-carbon transfer reactions, such as nucleotide synthesis, DNA methylation, amino acid metabolism, and lipid synthesis. Folate deficiency has been linked to risk for birth defects and certain types of cancer. Mammalian cells have developed an elaborate mechanism to harvest folate, involving extracellular folate receptors, a transmembrane carrier, and an enzymatic 'trapping' strategy to prevent folate from leaving the cell. The essential nature of folate would intuitively suggest that genes involved in folate transport and processing would be 'housekeeping' genes with expression in every cell. This is not the case: in the mouse, genes for folate receptors are expressed in very distinct tissue distributions during embryonic development. Functional requirements for folate receptors differ as well: A Folr1 mutation is embryonic lethal, yet mice lacking the Folr2 gene survive. A third folate receptor gene exists in the mouse - initially termed folbp3, but homologous to human FOLR4 - but functional information on this receptor is lacking. This project will investigate Folr4 function in the mouse through a gene knockout approach. We have generated mice with a 'floxed' allele of the Folr4 gene that allows us to either inactivate the gene in all cells, or in specific tissues only. In mice with a germline deletion of Folr4, we will determine the effects on embryonic development and survival, tissue differentiation, and, ultimately, folate metabolism. In addition to histological analyses, we will measure the effects on other folate receptor genes and on genes of the Folate metabolic pathway. The specific focus in tissue differentiation will be on developing cartilage, a site of high Folr4 expression in the embryo. We will examine cartilage development by general histological methods and in situ hybridization with cartilage-specific markers together with quantitative PCR. Primary chondrocytes from Folr4 knockout animals and controls will be assayed for expression of Folate pathway genes. These experiments will reveal how impaired folate transport affects cell growth and function in the embryo as a whole and in cartilage. The characterization of Folr4 knockout mice will provide the basis for future experiments involving tissue-specific Folr4 deletions as well as compound knockouts where more than one folate receptor gene is missing from the mouse genome. Together, these studies will improve our understanding of the basic biology of folate receptor genes, with implications for the prevention of human birth defects.
| Salbaum, J Michael; Kruger, Claudia; Kappen, Claudia (2013) Mutation at the folate receptor 4 locus modulates gene expression profiles in the mouse uterus in response to periconceptional folate supplementation. Biochim Biophys Acta 1832:1653-61 |
| Salbaum, J Michael; Finnell, Richard H; Kappen, Claudia (2009) Regulation of folate receptor 1 gene expression in the visceral endoderm. Birth Defects Res A Clin Mol Teratol 85:303-13 |
