Submitted to: Physiological Genomics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/19/2009
Publication Date: 6/23/2009
Publication URL: http://physiolgenomics.physiology.org/cgi/content/abstract/00069.2009v1
Citation: Goetz, F.W., Rise, M.L., Rise, M., Goetz, G.W., Binkowski, F.P., Shepherd, B.S. 2009. Stimulation of Growth and Changes in the Hepatic Transcriptome by Estradiol-17-Beta in the Yellow Perch (Perca flavescens). Physiological Genomics. Available: http://physiolgenomics.physiology.org/cgi/content/abstract/00069.2009v1. Interpretive Summary: Yellow perch have a high commercial value in the Great Lakes Regions and improvements in production efficiency of the U.S. perch industry would improve regional and global competitiveness and food safety (in part by decreasing imports of lesser quality Eurasian perch species). The yellow perch exhibits a sexual size dimorphism wherein females grow faster than males and this growth disparity can result in losses in productivity owing to increased labor and costs needed to grade out and feed poor growing cohorts. Studies have identified that the female sex steroid, estrogen, is a growth stimulator in yellow perch; however, the actual biochemical mechanisms by which estrogen promotes growth in males and females are not understood. To address this problem, we undertook a study wherein yellow perch were fed standard diets with or without (control) estrogen. After three months, those perch fed the estrogen-treated diet were substantially larger than untreated perch. To gain a better understanding of this phenomenon, we sequenced genes from the livers of the estrogen- and control-treated yellow perch and the number and type of genes were characterized. From these gene fragments, we have identified ~160 unique genes that fall into 30 metabolic categories in terms of their known functions in other animals. Among these 160 genes, 28 were significantly altered by estrogen treatment. Our findings demonstrate a linkage between growth and reproductive physiology in this species which involves an intricate relationship between estrogen and other growth regulating hormones. Development of these molecular tools will enable us to understand the involvement of these genes in commercially important physiological traits. Application of this knowledge in a selective breeding program is expected to lead to improvements in yellow perch production efficiency.
Technical Abstract: The effects of dietary estradiol-17-beta (E2) on growth and liver transcriptomics were investigated in the yellow perch (Perca flavescens). Following a 3-month treatment, E2 significantly stimulated an increase in length and weight of juvenile male and female perch relative to controls. The increase was significantly greater in females as compared to males. Separate, un-normalized cDNA libraries were constructed from equal quantities of RNA from 6 male and 6 female livers of E2-treated and control perch, and 3,546 and 3,719 ESTs were obtained respectively. To characterize E2-regulated genes, EST frequencies between libraries were calculated within contigs assembled from the combined ESTs of both libraries. Frequencies were also determined in EST gene groupings produced by aligning all of the ESTs from both libraries at the nucleotide level. From these analyses, there were 28 annotated genes that were regulated by 75% between libraries and for which there were at least 5 ESTs of the same gene between libraries. Regulation of 18 of these genes was confirmed by QPCR. Genes that were upregulated by E2 included reproductive-related proteins (vitellogenins and zona pelucida protein), binding proteins (serum lectin, nattectin, type II antifreeze protein, apolipoprotein E, microfibrillar associated protein), and proteases and protease inhibitors (aspartic protease, Kunitz-like protease inhibitor, and alpha-2-macroglobulin). While not part of the gene frequency analysis, QPCR showed significant upregulation of estrogen receptor esr1 and of IGF-1 in E2 livers. E2-downregulated genes represented a variety of functional categories including components of the respiratory chain (cytochrome b), lipid transport and metabolism (fatty acid binding protein, lipoprotein lipase), glycolysis (fructose-bisphosphate aldolase), amino acid and nitrogen metabolism (betaine homocysteine S-methyltransferase, urate oxidase), binding proteins (IGF binding protein-I and FBP32 (lectin)), a hydrolytic enzyme (chicken-type lysozyme), and a transcriptional regulator (GTP cyclohydrolase I feedback regulator). In perch, it appears that exogenous estrogen drastically shifts liver metabolism towards the production of lipoproteins and carbohydrate binding proteins, and that the growth-promoting action may involve an increase in hepatic IGF-1 production.