Key result
In 2-day-old rabbits, SERCA2 mRNA levels were 29-fold higher in cardiac muscle compared to stomach smooth muscle, indicating post-transcriptional and pretranslational control of expression.
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Cardiac muscle expresses sarcoplasmic/endoplasmic-reticulum Ca2+ pump isoform SERCA2a; stomach smooth muscle expresses SERCA2b. In 2-day-old rabbits, cardiac muscle contained levels of SERCA2 protein that were 100-200-fold those in the stomach smooth muscle. In nuclear run-on assays, the rate of SERCA2 gene transcription in heart nuclei was not significantly higher than in the stomach smooth-muscle nuclei. However, the SERCA2 mRNA levels (mean+/-S.E.M.) were (29+/-4)-fold higher in the heart. In both tissues the SERCA2 mRNA was associated with polyribosomes. In a sucrose-density-gradient sedimentation velocity experiment on polyribosomes, there was no difference in the sedimentation pattern of SERCA2 mRNA between the two tissues, suggesting that the translation efficiency of SERCA2 RNA in the two tissues is quite similar. Thus the main difference in the control of SERCA2 expression in the two tissues is post-transcriptional and pretranslational.
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Misquitta et al. (1999) studied this question. Cardiac muscle vs. Stomach smooth muscle was evaluated on SERCA2 mRNA levels (29+/-4-fold higher). In 2-day-old rabbits, SERCA2 mRNA levels were 29-fold higher in cardiac muscle compared to stomach smooth muscle, indicating post-transcriptional and pretranslational control of expression.
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