Molecular characterization and sex-specific tissue expression of prolactin, somatolactin and insulin-like growth factor-I in yellow perch (Perca flavescens)

Authors: LYNN, SCOTT - UNIVERSITY OF KENTUCKY; Shepherd, Brian

Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2007
Publication Date: 3/15/2007
Citation: Lynn, S.G., Shepherd, B.S. 2007. Molecular characterization and sex-specific tissue expression of prolactin, somatolactin and insulin-like growth factor-I in yellow perch (Perca flavescens). Comparative Biochemistry and Physiology (Part B: Biochemistry and Molecular Biology). 147:412-427.

Interpretive Summary: The pituitary hormones growth hormone (GH), prolactin (PRL) and somatolactin (SL), and their intermediary Insulin-like growth factor-I (produced in the liver), are important hormones that control growth, adaptation, reproduction and immune function. However, very little is known regarding the involvement of these hormones in the physiology of yellow perch. More importantly, recent data indicate that GH does not promote growth in this species and knowledge of the function of this hormone, and others, are of particular importance to researchers working to enhance yellow perch growth and feed efficiency. Yellow perch have a high commercial value in the Great Lakes Regions and have (historically) comprised the largest inland fishery in the U.S. As a result of collapse, or reduced catches, in commercial fisheries there is a growing aquaculture industry to support increasing consumer demand that cannot be met from commercial fisheries alone. Consequently, improvements in growth and feed efficiency are of considerable importance to the U.S. perch industry since improved production efficiency would improve global competitiveness and food safety, in part, by decreasing imports of lesser quality Eurasian perch species. The present research describes the molecular cloning and expression patterns of pituitary PRL, SL (a new hormone, only present in fish) and liver IGF-I cDNA from the yellow perch. Development of these molecular tools will enable us to understand their involvement in commercially-important physiological traits. Application of this knowledge in a selective breeding program should lead to improvements in yellow perch production efficiency.

Technical Abstract: The cDNA sequence encoding prolactin (PRL), somatolactin (SL) and insulin-like growth factor-I (IGF-I) genes of the yellow perch were obtained using cloning and sequencing techniques. Brain, pituitary, gill, heart, liver, stomach, kidney, spleen, muscle and gonad tissues were analyzed from both male and female adult yellow perch for tissue-specific expression. The full length cDNA of yellow perch PRL consists of 2,306 bp. The open reading frame encoded a protein of 211 amino acids, which included a putative signal peptide of 24 amino acids and a mature protein of 187 amino acids. PRL expression was highest in the yellow perch pituitary with low to moderate expression in other tissues including brain, gill and post-vitellogenic oocytes. The full length cDNA of yellow perch SL consists of 1,589 bp. The open reading frame encoded a protein of 231 amino acids, which included a putative signal peptide of 24 amino acids and a mature protein of 207 amino acids. SL expression was highest in the yellow perch pituitary with low to moderate expression in other tissues including brain, gill, liver, stomach, spleen and kidney. The full length cDNA of yellow perch IGF-I consists of 814 bp. The open reading frame encodes a protein of 186 amino acids, which included a putative signal peptide of 44 amino acids, an E domain of 74 amino acids and a mature protein of 68 amino acids, consisting of a B domain (29 aa), C domain (10 aa), A domain (21) and a D domain (8 aa). Tissue expression analysis of yellow perch IGF-I revealed a second yellow perch transcript that has an E domain approximately 80 nucleotides smaller and corresponds to Eurasian perch IGF-Ia. Both IGF-Ib and IGF-Ia had the greatest expression in liver tissue with moderate expression in brain, spleen and kidney tissues of both sexes. However, both yellow perch IGF-Ib and IGF-Ia showed distinct sex-specific tissue expression with IGF-Ia being expressed in most male tissues and several female tissues expressing only the IGF-Ib variant. These sequences are valuable molecular tools which can be used in future studies investigating the basis for sexually dimorphic growth in yellow perch.