AJP - Cell Physiology, Vol 261, Issue 6 C1091-C1098, Copyright © 1991 by American Physiological Society
Mitochondrial DNA replication and transcription are dissociated during embryonic cardiac hypertrophy
J. M. Kennedy, S. R. Lobacz and S. W. Kelley
Department of Physiology and Biophysics, University of Illinois, Chicago 60680.
Cardiac hypertrophy was produced in embryonic chicks by decreasing the
incubation temperature from 38 degrees C to 32 degrees C on day 11.
Increases in ventricular protein, RNA, and DNA support the cardiac
enlargement. Cytochrome-c oxidase activity and citrate synthase activity
were depressed in hypothermic ventricles by 63% and 56%, respectively. No
significant differences were seen in enzyme activities in pectoralis
muscles. The involvement of mitochondrial gene replication and
transcription was evaluated using a cDNA clone for the mitochondrially
encoded subunit III of cytochrome-c oxidase (CO III). Quantitative
slot-blot analysis demonstrated that the relative CO III mRNA concentration
was reduced in hypothermic ventricles. In contrast, the relative
mitochondrial DNA concentration was increased in hypothermic ventricles.
Taken together, these data indicate that a hypothermia-induced decrease in
cytochrome-c oxidase activity is associated with a decrease in CO III mRNA,
which is not coupled to a decrease in the mitochondrial DNA copy number.
This dissociation of mitochondrial gene replication and transcription may
provide a useful model for examining the regulation of mitochondrial
biogenesis.
