Growth and Development: Regulation of Adipogenesis and Adipose Tissue Development

The regulation of site and rate of fat deposition in cattle is not well defined. The study objective was to investigate adipogenic differentiation state-specific gene expression in feedlot cattle (>75% Angus; <25% Simmental parentage) of varying adipose accretion patterns. Four groups of 4 steers were selected from a group of 80 steers via ultrasound to have low backfat-low intramuscular fat (LBF-LIM), low backfathigh intramuscular fat (LBF-HIM), high backfat-low intramuscular fat (HBF-LIM), or high backfat-high intramuscular fat (HBF-HIM). Adipose tissue from the subcutaneous (SQ) and intramuscular (IM) depots were collected at harvest. The relative expression of adipogenic differentiation state-specific genes were evaluated using quantitative PCR. Data were analyzed using the mixed model of SAS and gene expression data were analyzed using covariate analysis with ribosomal protein L19 as the covariate. No interactions were observed (P > 0.10) between IM and SQ adipose accretion for any of the variables measured. Therefore, only the main effects of high and low accretion within a depot and the effects of depot are reported. No differences (P > 0.10) in mRNA between high and low adipose accretion within a depot were detected for any of the genes in spite of differences (P < 0.001) in cell density, diameter, and carcass measures. Preadipogenic delta like kinase 1 mRNA was higher (P < 0.001) in the IM than the SQ adipose tissue; conversely, differentiating and adipogenic genes (lipoprotein lipase, peroxisome proliferator activated receptorγ, fatty acid synthetase, and fatty acid binding protein 4) were higher (P < 0.001) in the SQ than the IM depot. Intramuscular adipocytes were smaller (P < 0.001) than SQ adipocytes and had greater (P < 0.001) expression of preadipogenic markers, indicating that more hyperplasia was occurring in the IM while the SQ was undergoing differentiation and hypertrophy. Adipogenic differentiation state-specific gene expression was not different in cattle with various phenotypes but adipogenesis in the SQ and IM adipose tissues appears to occur independently.