Differences in transcript abundance of genes on BTA15 located within a region associated with gain in beef steers

Using results from a previous GWAS, we chose to evaluate seven genes located within a 229Kb region on BTA15 for variation in RNA transcript abundance in a library of tissue samples that included adipose, liver, rumen papillae, spleen, muscle, and small intestine epithelial layers from the duodenum, ileum and jejunum collected from steers (n = 14) with positive and negative residual GN near mean dry matter intake (DMI). The genes evaluated were two olfactory receptor-like genes (LOC525033 and LOC618173), RRM1, STIM1, RHOG, PGAP2, and NUP98. The rumen papillae transcript abundance of RHOG was positively correlated with residual GN (P = 0.02) and ruminal STIM1 exhibited a trend towards an association with residual GN (P = 0.08). The transcript abundance of one olfactory receptor (LOC618173) in the ileum was also positively associated with residual GN (P = 0.02) and PGAP2 and LOC525033 in the ileum displayed trends for association with GN (P ≤ 0.1). To further evaluate the differential expression detected in the ileum and rumen of these animals, the transcript abundance of STIM1 and RHOG in the rumen and of PGAP2 and the olfactory receptors in the ileum were assessed in an additional group of 32 animals with divergent average daily gain (ADG) and average daily feed intake (ADFI) collected over two groups. The olfactory receptor, LOC525033, was not expressed in the ileum for the majority of these animals. Only RHOG showed a slight, but non-significant trend towards greater expression in animals with greater gain. We have detected differences in the transcript abundance of genes within this region in the rumen and ileum of animals selected for greater and less residual gain; however, we were unable to validate the expression of these genes in the larger group of cattle possibly due to the differences in phenotype or contemporary group.