TARGETED DISRUPTION OF THE MURINE DIHYDROLIPOAMIDE DEHYDROGENASE GENE(DLD) RESULTS IN PERIGASTRULATION LETHALITY

The Did gene product, known as dihydrolipoamide dehydrogenase or the E 3 component, catalyzes the oxidation of dihydrolipoyl moieties of four mitochondrial multienzyme complexes: pyruvate dehydrogenase, alpha-ke toglutarate dehydrogenase, branched-chain alpha-ketoacid dehydrogenase , and the glycine cleavage system, Deficiency of E3 activity in humans results in various degrees of neurological dysfunction and organic ac idosis caused by accumulation of branched chain amino acids and lactic acid, In this study, we have introduced a null mutation into the muri ne Did gene (Dld(tm1mjp)). The heterozygous animals are shown to have approximately half of wild-type activity levels for E3 and all affecte d multienzyme complexes but are phenotypically normal, In contrast, th e Dld(-/-) class dies prenatally with apparent developmental delay at 7.5 days postcoitum followed by resorption by 9.5 days postcoitum. The Dld(-/-) embryos cease to develop at a time shortly after implantatio n into the uterine wall when most of the embryos have begun to gastrul ate, This null phenotype provides in vivo evidence for the requirement of a mitochondrial oxidative pathway during the perigastrulation peri od, Furthermore, the early prenatal lethal condition of the complete d eficiency state may explain the low incidence of detectable cases of E 3 deficiency in humans.