Hardiman and Baker labs develop a multi-gene cross species microarray to screen the effects of environmental chemicals in fish, for which there is minimal genomic information. The array included genes that are involved in the actions of adrenal and sex steroids, thyroid hormone, and xenobiotic responses. This provides a sensitive tool for screening for the presence of chemicals with adverse effects on endocrine responses in coastal fish species.
Endocrine disruptors are chemicals that normal functioning of the endocrine system. Examples of endocrine disruptors of great current concern are plasticizers such as phthalates and alkylphenols, pesticides, fungicides, detergents, dioxin, polychlorinated biphenyls and pharmaceuticals, such as the synthetic estrogen 17α-ethynylestradiol. These xenobiotics are discharged into rivers, lakes and the ocean, where they accumulate in aquatic species. Humans and wildlife are exposed to these compounds directly and through fish and shellfish consumption. In addition, humans are exposed to endocrine disruptors via polluted drinking water.
Some endocrine disruptors interfere with normal endocrine responses because the chemical has structural similarities to hormones such as steroids. As a result these endocrine disruptors bind to a hormone receptor or to an enzyme that catalyzes hormone synthesis or degradation (1). Exposure of humans to endocrine disruptors may lead to intellectual impairment in children, premature puberty in females, and decreased reproductive ability in men (2). An endocrine disruptor of concern is nonylphenol, which is widely dispersed in the environment and which acts as an estrogen (3).
A recent analysis of male hornyhead turbot fish collected off of the coast of Southern California by the Hardiman and Baker laboratories at UCSD highlighted the effects of endocrine disruption (4). Morphological abnormalities, high levels of vitellogenin and estradiol, low levels of cortisol, and histological abnormalities, such as the presence of immature oocytes (eggs) within the testis were reported (Table 1). Control fish from a monitoring station in Dana Point, CA an area considered relatively non-impacted lacked any abnormalities (Table 1).
Aquatic Endocrine Disruption Characteristics of hornyhead turbots sampled from The Orange County (OCSD) and Los Angeles County (LACSD) sanitation districts. Cortisol, estradiol, insulin like growth factor (IGF-1), thyroxine (T4),vitellogenin (VTG) levels are indicated. Morphological lesions (not caused during capture) and maturity stages are noted.
Abnormalities are denoted by a
We have focused on two aquatic models. The first is zebrafish (Danio rerio), an important model organism in scientific research whose genome is completely sequenced. The second uses a Southern California coastal fish hornyhead turbot (Pleuronichthys verticalis), which is a key sentinel fish species used by environmental agencies in California to characterize the presence of chemicals in the marine environment.
A challenge with either microarray or qRT-PCR studies of gene expression in turbot, however, is the paucity of genomic sequence data. To overcome this problem, we searched GenBank for sequences in other fish to find regions of sequence conservation and fabricated a first generation microarray platform that was successful in detecting altered gene expression in multiple fish species (4, 6).
This microarray was used to study gene expression in wild hornyhead turbot, from polluted and clean coastal waters and in laboratory male zebrafish following exposure to estradiol and 4-nonylphenol
A: Cross species applicability of the Multi-Species Endocrine Microarray. Alterations in gene expression in zebrafish liver after a two week exposure to either 4-nonylphenol or estradiol using the multi-species endocrine microarray.
B: Gene expression changes were investigated in male turbot liver collected in two coastal monitoring stations in Orange County (OCSD) and Los Angeles County (LACSD) in California that are considered contaminated. Control fish were obtained from a monitoring station in Dana Point The fold changes observed between exposed and control fish in A and B are depicted as a heat map.
