Exploring the effect of exercise on the transcriptome of zebrafish larvae (Danio rerio)

In adult vertebrates, endurance training leads to physiological, metabolical and molecular adaptations which improve endurance performance. Only very few studies have focused on adaptive responses to endurance training during early vertebrate development, and molecular data is limited. Here, we explored the effect of swim-training on the transcriptome of the zebrafish during early development on a quantitative and spatial gene expression level. We subjected larval zebrafish from 5 to 14 dpf (days post fertilization) to swim-training and performed a whole genome microarray analysis of trained and control fish sampled at 10 dpf. In addition, we investigated if swim-training affected the expression of genes involved in muscle growth and structure with quantitative real-time PCR in trained and control fish sampled at 5 and 14 dpf. To obtain a general overview of the effects of swim-training on the transcriptome, we selected 52 genes from the whole genome microarray analysis based on a number of criteria. In situ hybridization demonstrated that 15 genes were specifically expressed in the brain, muscle, kidneys, liver, pancreas or intestines. Thus, swim-training led to molecular changes already after 6 days of swim-training and in a variety of organ systems. In addition, the expression of slow fiber markers was increased after 10 days of swim-training, indicating that muscle can already shift towards a slow aerobic phenotype during zebrafish larval development. Taken together, this study demonstrates that significant changes occur, even at early stages, as an adaptive response to endurance training during early vertebrate development.