RNA-seq analysis of differential gene expression in muscle from angus beef steers undergoing diet restriction and compensatory growth
The objective of this study was to examine changes in muscle gene expression of growing steers during a period of dietary energy restriction followed by a period of realimentation. Crossbred Aberdeen Angus x Holstein Friesian (n = 24) steers were assigned to one of two feeding treatments. Over a 99 d period, 1 group (n=12) was offered a high energy control diet consisting of concentrates ad libitum and 7 kg of grass silage per head daily. The second group (n=12) was offered an energy restricted diet consisting of grass silage ad libitum plus 0.5 kg of concentrate per head per day. From the end of the differential feeding period (99 d), both groups of animals were offered a total mixed ration (grass silage:concentrate ratio of 80:20). This period, which lasted 200 d, was known as the realimentation period. All animals were slaughtered on d 299 of the study. Muscle biopsies were collected at 2 time points (end of the differential feeding period (d 99) and during the realimentation period (d131). RNA was extracted and muscle gene expression was examined using RNA-seq technology and bioinformatic analysis. During the differential feeding period, 17 over-represented pathways were identified, including the peroxisome proliferator activated receptor signalling, glycolysis/ gluconeogenesis and metabolic pathways controlling the metabolism of lipids and lipoproteins which indicate reduced energy intake and fat tissue accumulation occurring in muscle tissue during the restriction phase. During the realimentation period, 164 differentially expressed genes were annotated to 9 over-represented pathways including starch and sucrose metabolism, carbohydrate digestion and absorption and TGF-ß signalling pathway. It is hypothesised that the signalling effects of the TGF-ß pathway were reduced thereby promoting accelerated cell growth and proliferation in muscle tissue of animals experiencing compensatory growth. This information can be exploited in genomic breeding programmes to assist selection of cattle with a greater ability to compensate following a period dietary restriction. Overall design: 24 muscle RNA samples were analysed in total. 6 samples were from muscle biopsies collected at the end of a period of dietary restriction (d99) and 6 samples were from muscle biopsies collected at the peak of compensatory growth (d131). In addition, RNA was also analysed from 6 samples collected from animals fed ad libitum at each of these two timepoints.