Transcriptional Response of Bioenergetic Genes to Exercise
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Transcriptional responses to stressors are typically measured as changes in mRNA levels, despite a broad awareness that transcript levels do not equate to transcription rates. I was able to use goldfish (Carassius auratus) to assess the impact of a single exercise bout on transcription and transcript levels by measuring unprocessed mRNA (pre-mRNA) and mature mRNA levels for critical bioenergetics genes in red and white muscle tissue. I examined housekeeping genes (β-actin: BACT and tubulin: TUB) and select genes for mitochondrial metabolism (citrate synthase: CS and cytochrome c oxidase subunit 4-1: COX4-1), and hexokinase II: HXK. In red muscle, I found that the transcript level for mitochondrial genes (CS and COX4-1) and the housekeeping gene BACT does not change significantly regardless of exercise intensity, but that there is an increase in pre-mRNA levels for these genes at the highest exercise intensity. HXK mRNA showed complex patterns. The mature HXK mRNA increased after a 3 h bout of exercise at the highest exercise intensity (in red and white muscle) but only in recovery after exhaustive exercise in white muscle. The increases in HXK pre-mRNA occurred following exercise and after recovery (in red muscle) and after a period of recovery (in white muscle). In red muscle, exercise didn’t increase the mRNA for any gene within a recovery period of 1 h, except exercise at 80% Ucrit. Analysis of white muscle tissue after a 3 h bout of exercise indicated that there was no change in COX4-1 mRNA post exercise or after recovery, a slight decrease in BACT mRNA after recovery, a significant increase in CS mRNA after recovery and a significant increase in HXK mRNA post exercise. Overall, I found that: the levels of pre-mRNA changed more dramatically than did mature mRNA, the greatest changes occurred at the highest exercise intensity, the increases were mainly seen in recovery rather than during exercise, and there was a greater response in the pathways and tissues that are recruited during the exercise activity.