Research Interests

The main research focus for my laboratory is to understand the molecular mechanisms by which endocrine disruptors affect biological systems. From field studies in lakes in central Florida, we have developed a largemouth mass model for reproductive parameters, for both males and females, to describe the normal cyclic flux of hormones and other reproductive biomarkers.. We have also studied how these may vary in contaminated environments. We plan to continue this research to further understand the molecular mechanisms of endocrine disruption that occur when fish are exposed to chlorinated hydrocarbons. The overall hypothesis is that exposing fish to certain chlorinated hydrocarbons alters critical points in the regulation of genes important in reproduction and development.

The natural action of hormones occurs at the molecular level in target tissues. Each hormone induces the synthesis of a subset of mRNAs that encode proteins for specific functions. In fish liver, for example, estrogen induces the synthesis of vitellogenin, the egg-yolk precursor protein that females make during oogenesis. In addition to vitellogenin, estrogen induces the synthesis of its own receptor and a variety of additional proteins, such as the vitellin envelope proteins, that females require at this stage of reproduction. Males exposed to estrogen or to an estrogen mimic also respond at the molecular level by synthesizing mRNAs for specific proteins. In order to understand the mechanisms of toxicity associated with each hormonal mimic, it is critical to study the coordinate expression of the set of mRNAs which are induced by each treatment and to determine whether this induction is pathological. And more importantly it is critical to determine which hormone or hormones a xenobiotic is mimicking. Some xenobiotics appear to act by more than one mechanism. DDE, for example, has been described as having both weak estrogen-like and anti-androgen-like properties. We will examine both strong estrogens (E₂, DES, EE₂) and weak estrogens (methoxychlor, nonylphenol and DDE) for their potential to disrupt the endocrine system.

Specific Objectives of my Research:

1. Measure the coordinate expression of mRNAs for vitellogenin, vitellin envelope proteins, and estrogen receptor in mature female and male largemouth bass exposed in the laboratory to environmental levels of strong and weak estrogen mimics. Determine whether largemouth bass express both an estrogen receptor alpha and beta and other splicing variants. Determine whether exposure to EDCs alters the ratio of these variants in critical tissues.

2. Using a primary hepatocyte system, determine the molecular consequences of exposure in vitro. Determine mRNA stability parameters and metabolic consequences for each contaminant.

3. Establish mRNA induction fingerprints for each contaminant using differential display rt-PCR. We will examine the possibility that some genes are induced at very low concentrations of hormones and suppressed at higher concentrations to understand the inverted U dose response curve that has been postulated in the literature.

4. Determine the consequences of exposure on egg quality, F1 and F2 progeny, and capacity to reproduce under the highly contaminated field conditions existing in various superfund areas in Florida and in muck farms around Lake Apopka. Apply new biomarkers and mRNA fingerprints to animals exposed in the field.