RNA-Seq Analisys of the Exercise Transcriptome in Horses: Insights on Transcribed Exons, Introns and Repeats

The horse is probably the best animal model for investigating genomic response to exercise-induced stress, due to its natural aptitude for athletic performance and the relative homogeneity of its genetic background. We applied RNA-seq to PBMCs of six 3 years old race horses sex matched collected at rest and after a 2000-meter competition. 
We observed a transcription shift from coding to non-coding regions therefore we separately analyzed exon and intron compartments. 
In both analyzed compartments, network and GO analysis revealed mechanisms known to be activated by stress as well as functions to preserve energy devoted to other processes.

A large number of transcripts, corresponding to intergenic and intronic regions associated with new transcriptional elements, were identified. This data might be correlated with transcriptional activity related to nascent transcription, co-transcriptional splicing events or transcription of long noncoding RNAs or enhancer RNAs that are know to contribute to changes in intronic read counts.
We observed a post-race increase of reads mapping to repeats, especially to LINE1 in intergenic and intronic regions.

Our results reinforce the hypothesis that transposable elements (TE) and intronic sequences may serve as transcriptional units capable of enriching transcriptomes with limited genomic resources, such under stress conditions. We also found that 9 full-length LINE1 elements are up-regulated after the race. This suggests that a great effort induced by exercise may - in principle - activate LINE1 retrotransposition, as already demonstrated in human and mouse tissues and in certain sporadic cancers. 


Supported by MIPAAF, grant INNOVAGEN, and by AGRIS.