R3 AM Ecotoxicogenomics of Emerging Chemical Issues
Thursday, 17 November 2005: 8:00 AM - 11:40 AM in Ballroom 3

(LYN-1117-744420) Cloning, tissue-specific expression and responses to 17-estradiol of key endocrine genes in yellow perch (Perca flavescens).

Lynn, Scott¹, Malison, Jeffrey², Shepherd, Brian³, Birge, Wesley¹, ¹ University of Kentucky, Lexington, KY, USA² University of Wisconsin-Madison, Madison, WI, USA³ National Cool and Cold Water Aquaculture Research Station USDA, Kearneysville, WV, USA

ABSTRACT- Yellow perch (Perca flavescens) are an ecologically important teleost species found in high abundance in Lake Erie. They exhibit an interesting estrogen-stimulated, sexually dimorphic growth pattern wherein females grow faster than males. To gain better understanding of the endocrine system in yellow perch, we used RACE techniques to clone several genes associated with sexual development, reproduction and growth. These include the pituitary hormones prolactin (PRL) and somatolactin (SL), the growth hormone intermediates insulin-like growth factors-I & -II (IGF-I & -II), the estrogen receptors (- & -ERs) and aromatase. We also developed quantitative real-time PCR assays to measure gene expression levels. Female 0+ year yellow perch were exposed to 20 mg/kg 17-estradiol (E₂) via the diet and individuals were sampled on days 7 and 28. Fish were weighed, measured and pituitary, liver and ovary tissues were harvested. A control group of female 0+ year yellow perch was reared under the same conditions (21°C, 16/8 L/D, fed ad libitum) with concurrent samplings. None of the pituitary genes measured (GH, PRL or SL) showed a significant response to E₂ treatment at day 28. E₂ responses in the liver include a significant increase in ER expression at both day 7 and 28. However, liver ER expression was significantly down regulated in the E₂ treatment at day 7 with no difference from control at day 28. Surprisingly though, E₂ treatment did not cause significant changes (increase or decrease) in any of the genes measured in ovary (aromatase, ER or ER) at day 7. However E₂ treatment did cause a slight non-significant down regulation of aromatase, ER and ER expression at day 28. Our work on yellow perch can provide predictive capabilities for estrogen-dependent physiological processes in other species of teleosts and can also make yellow perch an exciting option for future ecotoxicogenomic studies.

Key words: RACE cloning, estrogen, endocrine, real-time PCR