Identification of Genes Differentially Expressed in Both Sheep and Cattle Muscle by Combined Trenbolone Acetate and Estradiol-17beta Implants

We have identified a highly significant overlap between the top 500 genes with higher levels of expression in the longissimus muscle (LM) of trenbolone acetate and estradiol-17 beta implanted sheep and both of two previously published equivalent cattle data sets (P = <<0.00005). The common up-regulated genes included GREB1, WISP2, CRYBB2, LBP and HES6, encoding proteins involved in cell proliferation and growth. The overlap between the top 500 genes with lower levels of expression was highly significant with cattle from Western Australia (P = <<0.00005), but much less significant with cattle from New South Wales (P = 0.039). Amongst the latter genes in sheep and WA cattle were PPARGC1A, PDK4 and CEBPD, which encode proteins involved in the regulation of metabolic activity. These genes and 11 additional common down-regulated genes exhibit highly correlated expression across the whole cattle dataset. A second large group of 20 genes with correlated expression, including monocyte lineage markers CD14, CD48, CD53 and CD163, were also down-regulated. These genes appear to report a reduction in the number of monocytes, or monocyte derived cells, associated with LM in the treated animals. The majority of genes in the triacylglyceride synthesis and storage module were also expressed at lower levels in the LM of treated sheep, albeit with a much smaller reduction than in cattle. Similar to cattle a small shift towards slow twitch fibre subunit expression was observed, as was a lack of effect on the expression of pro-myogenic transcription factors and genes encoding muscle atrogins.