ABSTRACT
Patients with mutations in MMACHC have the autosomal recessive disease of cobalamin metabolism known as cblC. These patients are unable to convert cobalamin into the two active forms, methylcobalamin and adenosylcobalamin and consequently have elevated homocysteine and methylmalonic acid in blood and urine. In addition, some cblC patients have structural abnormalities, including congenital heart defects. MMACHC is conserved in the mouse and shows tissue and stage-specific expression pattern in midgestation stage embryos. To create a mouse model of cblC we generated a line of mice with a gene-trap insertion in intron 1 of the Mmachc gene, (Mmachc(Gt(AZ0348)Wtsi)). Heterozygous mice show a 50% reduction of MMACHC protein, and have significantly higher levels of homocysteine and methylmalonic acid in their blood. The Mmachc(Gt) allele was inherited with a transmission ratio distortion in matings with heterozygous animals. Furthermore, homozygous Mmachc(Gt) embryos were not found after embryonic day 3.5 and these embryos were unable to generate giant cells in outgrowth assays. Our findings confirm that cblC is modeled in mice with reduced levels of Mmachc and suggest an early requirement for Mmachc in mouse development.
Subject(s)
Carrier Proteins/genetics , Embryonic Development/genetics , Alleles , Amino Acid Metabolism, Inborn Errors/genetics , Animals , Female , Gene Order , Gene Targeting , Genetic Vectors/genetics , Genotype , Hyperhomocysteinemia/genetics , Male , Mice , Oxidoreductases , PhenotypeABSTRACT
Vitamin B(12) (cobalamin, Cbl) is required for cellular metabolism. It is an essential coenzyme in mammals for two reactions: the conversion of homocysteine to methionine by the enzyme methionine synthase and the conversion of methylmalonyl-CoA to succinyl-CoA by the enzyme methylmalonyl-CoA mutase. Symptoms of Cbl deficiency are hematological, neurological and cognitive, including megaloblastic anaemia, tingling and numbness of the extremities, gait abnormalities, visual disturbances, memory loss and dementia. During pregnancy Cbl is essential, presumably because of its role in DNA synthesis and methionine synthesis; however, there are conflicting studies regarding an association between early pregnancy loss and Cbl deficiency. We here review the literature about the requirement for Cbl during pregnancy, and summarized what is known of the expression pattern and function of genes required for Cbl metabolism in embryonic mouse models.
Subject(s)
Embryonic Development/drug effects , Vitamin B 12/blood , Vitamin B 12/pharmacokinetics , 5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase/metabolism , Acyl Coenzyme A/metabolism , Animals , Disease Models, Animal , Female , Homocysteine/metabolism , Humans , Methionine/biosynthesis , Methylmalonyl-CoA Mutase/metabolism , Mice , Pregnancy , Vitamin B 12 Deficiency/bloodABSTRACT
Organ-specific birth defects are seen in patients with some inborn errors of vitamin B(12) metabolism. To determine whether three mouse genes, whose human counterparts are associated with isolated methylmalonic aciduria (Mmaa, Mmab and Mut), show tissue-specific expression during organogenesis, we used in situ hybridization to characterize their pattern of expression in wild type embryos and placentas at embryonic days (E) E10.5, E11.5 and E12.5. These three genes are ubiquitously expressed in the placenta and in embryos at E10.5. At E11.5, we observed tissue specific expression patterns for these three genes in lung, head and Rathke's pouch. At E12.5, although Mut expression was ubiquitous, we found cell-type specific expression patterns for Mmaa and Mmab in the developing craniofacial region, the lung, the liver, and the gut. These results suggest that during organogenesis the proteins encoded by these three genes may interact in only a subset of cells.
