M9 AM Ecotoxicology of Reptiles
Monday, 14 November 2005: 8:00 AM - 11:40 AM in 339-340

(UNR-1117-557362) Molecular mechanisms involved in maternal transfer of selenium in the western fence lizard (Sceloporus occidentalis).

Unrine, J¹, Jackson, B², Hopkins, W³, Romanek, C^{1, 4}, ¹ The University of Georgia, Savannah River Ecology Laboratory, Aiken, SC, 29803² Dartmouth College, Hanover, NH, USA³ Virginia Polytechnic Institute and State University, Blacksburg, VA, USA⁴ The University of Georgia, Department of Geology, Athens, GA, USA

ABSTRACT- Selenium (Se), an essential trace element, is teratogenic when concentrations in vertebrate embryo tissue become elevated. Little is known about the molecular mechanisms by which Se is transferred from mother to offspring in vertebrates. Two previous studies have demonstrated the incorporation of Se into yolk proteins in white sturgeon (Acipenser transmontanus) and ovalbumen in domestic chicken (Gallus gallus) eggs. Using size exclusion chromatography and dynamic reaction cell inductively coupled plasma mass spectrometry (SEC-DRC-ICP-MS), we demonstrated that Se is incorporated into at least four egg proteins in western fence lizards (Sceloporus occidentalis) exposed to dietary selenomethionine. Simultaneous quantification of sulfur (S) indicated that Se content in egg proteins depended on their S content, suggesting substitution of Se for S in amino acids. Monitoring the phosphorus (P) signal helped to identify the fractions which were likely to contain the egg phosphoproteins vitellogenin (VTG), lipovitellin (LV) and phosvitin (PV). The molecular weights of Se containing proteins were determined by denaturing polyacrylamide gel electrophoresis (SDS-PAGE) and non-denaturing gradient PAGE. One protein was a monomer of MW 314 kD which is likely VTG, the second a homodimer with a subunit MW of 120 kD which is likely LV, the third was a monomer with a MW of 62 kD. Each of these three proteins appeared to be highly phosphorylated. The fourth protein was a heterodimer with subunit MWs of 20 and 22 kD. The 62 kD and 44 kD proteins were present in follicles that did not contain the 314 and 220 kD proteins. The identity and function of these latter two proteins are unknown but they may be part of a mechanism of maternal transfer of Se that is independent of vitellogenesis. This was the first study to demonstrate molecular mechanisms involved in maternal transfer of Se in a reptile, a process that is poorly understood at best in vertebrates. This study demonstrates the utility of reptiles as a model for addressing basic ecotoxicological questions. Future studies will confirm the identity of these proteins using mass spectrometric approaches and investigate their roles in determining maternal transfer and teratogenicity of Se.

Key words: Maternal transfer, Selenium, ICP-MS, Reptile