To investigate genes involved in intramuscular adipogenesis in ruminants, 16 genes with dramatic variable expression were selected. These were selected from the differentiation- and proliferation-phase libraries of our previous serial analysis of gene expression (SAGE) studies of a clonal bovine intramuscular preadipocyte (BIP) cell line. We harvested the BIP cells over 12 days after adipogenic stimulation with all-trans retinoic acid (ATRA). Quantitative real-time PCR confirmed the earlier SAGE study results of the expression patterns of 15 of the genes. On day 6, TG accumulation increased significantly in the BIP cells but was completely inhibited in the 3T3-L1 cells (the monogastric reference). ATRA enhanced expression levels of six genes whereas it suppressed expression of eight genes on day 3 of adipogenesis in the BIP cells. Forty-eight hours after transfection, the messenger RNA expression level of the adipose differentiation-related protein (ADFP), encoded by one of the upregulated genes, in the ADFP small interference RNA (siRNA)-transfected cells was 3.5% of that in negative control-transfected cells. Also, 6 days after induction the TG level in the ADFP siRNA-transfected cells was 21.8% lower than that in negative control-transfected cells. This analysis of gene expression profiles after ATRA treatment will contribute to our understanding of the molecular mechanisms involved in bovine intramuscular adipogenesis.

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Beef marbling is caused by intramuscular deposition and it is an economically important trait in the beef industry. Vitamin A (VA) is an important feed supplement for cattle, but it can hinder marbling if provided in excess. In cattle, VA forms various derivatives such as all-trans retinoic acid (ATRA) and 9-cis retinoic acid (9cRA). Therefore, we investigated the genes involved in bovine intramuscular adipogenesis after VA treatment with ATRA and 9cRA. Differential gene expression levels were validated by microarray analysis in a clonal bovine intramuscular preadipocyte (BIP) cell line derived from the intramuscular adipose tissue of Japanese Black cattle. BIP cells were harvested 6 days after adipogenic stimulation with either 1 μmol/L ATRA, 1 μmol/L 9cRA or non-retinoic acid control. The ATRA- and 9cRA-treated cells exhibited reduced transcription of genes involved in the circulatory system and muscle development compared with the no retinoic acid (RA) treatment. In addition, the ATRA- and 9cRA-treated cells exhibited increased transcription of genes involved in the immune system, protein kinase B signaling and responses to various stimuli. These results demonstrate the lower expression of muscle development in ATRA- and 9cRA-treated BIP cells during adipogenesis.