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BackgroundClenbuterol, a beta-agonist, can dramatically reduce pig adipose accumulation at high dosages. However, it has been banned in pig production because people who eat pig products treated with clenbuterol can be poisoned by the clenbuterol residues. To understand the molecular mechanism for this fat reduction, cDNA microarray, real-time PCR, two-dimensional electrophoresis and mass spectra were used to study the differential gene expression profiles of pig adipose tissues treated with/without clenbuterol. The objective of this research is to identify novel genes and physiological pathways that potentially facilitate clenbuterol induced reduction of adipose accumulation.ResultsClenbuterol was found to improve the lean meat percentage about 10 percent (P < 0.05). The adipose cells became smaller and the muscle fibers became thicker with the administration of clenbuterol. The mRNA abundance levels of 82 genes (ESTs) were found to be statistically differentially expressed based on the Student t-test (P < 0.05) in the microarray analyses which contained 3358 genes (ESTs). These 82 genes (ESTs) were divided into four groups according to their Gene Ontology Biological Process descriptions. 16 genes were cellular metabolism related genes (including five related to lipid metabolism such as apolipoprotein D and apolipoprotein R), 10 were signal transduction related genes, 45 were expressed sequence tags (ESTs) and 11 others were of various categories. Eleven of the 82 genes (ESTs) were chosen for real-time PCR analysis, with eight genes showing similar induction magnitude as that seen in the microarray data. Apolipoprotein R was also found to be up-regulated by the proteomic analysis.ConclusionPig fat accumulation was reduced dramatically with clenbuterol treatment. Histological sections and global evaluation of gene expression after administration of clenbuterol in pigs identified profound changes in adipose cells. With clenbuterol stimulation, adipose cell volumes decreased and their gene expression profile changed, which indicate some metabolism processes have been also altered. Although the biological functions of the differentially expressed genes are not completely known, higher expressions of these molecules in adipose tissue might contribute to the reduction of fat accumulation. Among these genes, five lipid metabolism related genes were of special interest for further study, including apoD and apoR. The apoR expression was increased at both the RNA and protein levels. The apoR may be one of the critical molecules through which clenbuterol reduces fat accumulation.

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The peroxisome proliferators-activated receptor-gamma coactivator-1alpha (PGC-1alpha) was investigated as a candidate gene for growth and fatness traits in chicken because of its prominent role in muscle fiber specialization and adipogenesis. A single nucleotide polymorphism (SNP) from G to A at position 646 of the open reading frame of chicken PGC-1alpha gene causing an Asp216Asn amino acid substitution was identified. The frequencies of alleles and genotypes were significantly different among 6 chicken breeds (P < 0.01). The White Plymouth Rock had the highest frequency (0.67) of allele G, whereas the White Leghorn had the lowest (0.18). The associations of the SNP with the growth and fatness traits were evaluated in 332 F(2) birds from an experimental cross of White Plymouth Rock x Silkies. No association was found between the SNP and growth-related traits. However, abdominal fat weight at 12 wk of age for birds with genotype GG was 34.26 and 28.71% higher than those with genotypes AA and AG, respectively (P < 0.01), indicating that the Asp216Asn polymorphism of the PGC-1alpha gene could be used as a novel potential molecular marker for selection against abdominal fatness without interfering in regular breeding for growth rate of chickens.

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