ENERGY DEPRIVATION AND A DEFICIENCY IN DOWNSTREAM METABOLIC TARGET GENES DURING THE ONSET OF EMBRYONIC HEART-FAILURE IN RXR-ALPHA(- -) EMBRYOS/

RXR alpha null mutant mice display ocular and cardiac malformations, l iver developmental delay, and die from cardiac failure around embryoni c day (E) 14.5 pc. To dissect the molecular basis of the RXR alpha-ass ociated cardiomyopathy, we performed subtractive hybridization and sys tematically characterized putative downstream target genes that were s electively lacking in the mutant embryos, both at early (E10.5) and la te (E13.5) stages of mouse embryonic development. Approximately 50% of the subtracted clones (61/115) encoded proteins involved in intermedi ary metabolism and electron transport, suggesting an energy deficiency in the RXR alpha(-/-) embryos. In particular, clone G1, which encodes subunit 14.5b of the NADH-ubiquinone dehydrogenase complex, displayed a dose-dependent expression in the wild-type, heterozygous and RXR al pha mutant mice. This gene was also downregulated in a retinoid-defici ent rat embryo model. ATP content and medium Acyl-CoA dehydrogenase mR NA were lower in RXR alpha mutant hearts compared to wild-type mice. U ltrastructural studies showed that the density of mitochondria per myo cyte was higher in the RXR alpha mutant compared to wild-type litterma tes. We propose a model whereby defects in intermediary metabolism may be a causative factor of the RXR alpha(-/-) phenotype and resembles a n embryonic form of dilated cardiomyopathy.