Peeling Back the Evolutionary Layers of Molecular Mechanisms Responsive to Exercise-Stress in the Skeletal Muscle of the Racing Horse

Abstract

The modern horse (Equus caballus) is the product of over 50 million yrs of evolution. The athletic abilities of the horse have been enhanced during the past 6000 yrs under domestication. Therefore, the horse serves as a valuable model to understand the physiology and molecular mechanisms of adaptive responses to exercise. The structure and function of skeletal muscle show remarkable plasticity to the physical and metabolic challenges following exercise. Here, we reveal an evolutionary layer of responsiveness to exercise-stress in the skeletal muscle of the racing horse. We analysed differentially expressed genes and their co-expression networks in a large-scale RNA-sequence dataset comparing expression before and after exercise. By estimating genome-wide dN/dS ratios using six mammalian genomes, and FST and iHS using re-sequencing data derived from 20 horses, we were able to peel back the evolutionary layers of adaptations to exercise-stress in the horse. We found that the oldest and thickest layer (dN/dS) consists of system-wide tissue and organ adaptations. We further find that, during the period of horse domestication, the older layer (FST) is mainly responsible for adaptations to inflammation and energy metabolism, and the most recent layer (iHS) for neurological system process, cell adhesion, and proteolysis.

Making Olympic lizards: the effects of specialised exercise training on performance

“…Research on non-human mammals has added to our general understanding of how exercise training affects muscle and cardiovascular tissue (e.g. Gollnick and King, 1969;Guy and Snow, 1977;Constable et al, 1987;Evans and Rose, 1988;Bebout et al, 1993;Kim et al, 2013). Nevertheless, research on 'exercise' in nonhuman, especially non-mammalian, vertebrates has lagged behind with regards to how exercise might alter the phenotype and influence the evolution of morphology and performance O'Connor et al, 2011;Sinclair et al, 2013;Lailvaux and Husak, 2014).…”

Comparative Transcriptomic Analyses by RNA-seq to Elucidate Differentially Expressed Genes in the Muscle of Korean Thoroughbred Horses

“…The candidate gene from the homeobox family HOXD10 regulates animal morphological diversity at the organismal and evolutionary level. It has been known that highly expressed genes evolve slowly [4]. Therefore, the difference in the expression of HOXD10 between the Jigusang Seryeok and Eonjena Taeyang horses may reflect morphological variations.…”

“…The preexercise samples were collected from the triceps brachii of the right leg of each horse. It was reported that a 30-min trot was equivalent to 17-18 min of cantering [4]. Therefore, in our study, a 30-min trot was considered for Eonjena Taeyang and Jigusang Seryeok.…”

“…The skeletal muscle structure of the Thoroughbred horse possesses remarkable plasticity to respond to environmental changes as well as to the physical and metabolic challenges during training and exercise [4]. Under racing conditions, coordinated stress responses arise through multiple genomic mechanisms.…”

“…The natural proclivity for athletic performance by horses and humans has prompted some researchers to consider the horse as a reference species for comparative studies to optimize physical training and disease prevention. Therefore, the Thoroughbred horse also can serve as an excellent model for human diseases [4,5].…”