Abundantly expressed genes in pig adipose tissue: An expressed sequence tag approach 1 C. H. Chen,* E. C. Lin,* W. T. K. Cheng,* H. S. Sun,† H. J. Mersmann, 2 and S. T. Ding* 3 *Department of Animal Science and Technology, National Taiwan University, Taipei 106, Taiwan; and †Institute of Molecular Medicine, National Cheng Kung University Medical College, Tainan 701, Taiwan ABSTRACT: Adipose tissue plays a critical role in metabolism, storage, and release of fatty acids in mam- mals. Construction of a full-length cDNA library is an effective way to understand the functional expression of genes in adipose tissue, and in addition, novel genes for further research can be found in the library. In this study, adipose tissue RNA was extracted from three 18- mo-old Lee-Sung pigs. The mRNA was isolated, reverse transcribed, and used to construct a cDNA library. After transformation, 2,880 clones were selected and se- quenced. Cluster analysis was performed, and the as- sembled contig of each cluster was subjected to search against DNA sequences in the nucleotide databases (NCBINR/TIGRGI). These sequences were clustered into 1,527 unique sequences; 80% of the sequences were categorized as known genes, and 20% of the sequences Key words: adipose tissue, expressed sequence tag, pig ©2006 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2006. 84:2673–2683 doi:10.2527/jas.2005-737 INTRODUCTION In mammals, the major functions of adipose tissue are to synthesize fatty acid de novo and to accumulate excess energy as fat. Recent research indicates that adipose tissue is also an endocrine tissue that secretes leptin, adiponectin, and other factors into the blood to regulate energy homeostasis (Mohamed-Ali et al., 1998; Havel, 2002). Porcine adipose tissue has abundant mRNA for adiponectin mRNA and its receptors (Ding et al., 2004; Wang et al., 2004) and produces leptin (Ramsay et al., 1998). These findings indicate that the adipose tissue in pigs also acts as an endocrine tissue and expresses genes involved in regulating metabolism and physiological functions in other tissues. 1 This work was supported in part by the Council of Agriculture in Taiwan. We thank W. M. Cheng for care and feeding of the animals. 2 Visiting scientist, National Taiwan University. 3 Corresponding author: sding@ntu.edu.tw Received December 19, 2005. Accepted May 3, 2006. 2673 were categorized as unknown genes. In this adipose tissue cDNA library, approximately 16% of the genes contained full-length sequences with start and stop co- dons. Gene ontology analysis was performed to indicate the possible functions of these genes. Genes associated with mitochondrial function were abundant and repre- sented 10% of the total. Several fatty acid transport genes and stearoyl coenzyme A desaturase were among the most abundant genes expressed. Tissue distribution of several abundant genes was analyzed by northern analysis, and many of these genes were transcribed in porcine adipose tissue in high copy number. Our full- length sequence data and tissue distribution data can be used to decipher the functional roles exhibited by the adipocyte under various perturbations via endocrine, environmental, genetic, nutritional, pharmacological, or physiological manipulations. The expressed sequence tag (EST) technique is an effective approach to study functional expression of genes in various cells and tissues (Adams et al., 1992). To understand the function of adipose tissue, an analy- sis of abundantly expressed genes in the tissue is needed. Mikawa et al. (2004) characterized 298 EST clones from pig adipose tissue. Today, the largest EST library related to porcine adipose tissue in the National Center for Biotechnology Information (NCBI) dbEST is a library (dbEST library ID.1316) with 2,155 sequences, which is not full-length enriched. The full-length cDNA sequences provide more reliable evidence for determin- ing the existence, structure, and function of a gene (The RIKEN Genome Exploration Research Group Phase II Team and the FANTOM Consortium, 2001; Mamma- lian Gene Collection Program Team, 2002). Therefore, we conducted this experiment to clone full- length-enriched cDNA sequences of genes expressed in porcine adipose tissue to test the hypothesis that in addition to housekeeping genes, the genes involved in metabolism are abundantly expressed in adipose tissue,