MITOCHONDRIAL GENE-EXPRESSION DURING BOVINE CARDIAC GROWTH AND DEVELOPMENT

The expression of both mitochondrial and nuclear genes encoding enzyme s involved in electron transport and oxidative phosphorylation was exa mined in bovine cardiac tissue during early growth, development and ag ing. The steady state lever of mRNAs for mitochondrial genes including ATPase 6, COXII and cyt b increased 2.5-4-fold relative to early feta l levels in late fetal and young adult tissues and showed a marked dec line (30-50%) in older adult tissues. Similar results were found with the nuclear genes, COXVB and ATP-beta synthase showing coordinate regu lation of the two genomes. An increase in mtDNA copy number correlated with the increase in transcript level. Enzyme activity levels for NAD H dehydrogenase and cytochrome c oxidase showed a similar trend, albei t of lesser magnitude. These activity levels contrasted with the activ ity level of an entirely nuclear-encoded mitochondrial enzyme, citrate synthase, which increased not only throughout development but in the older adult tissue. This study indicates that there is a pattern of in creasing mitochondrial and nuclear gene expression for OXPHOS enzymes in developing cardiac tissue and decreasing OXPHOS gene expression in the aging heart.