Octylphenol and UV-B radiation alter larval development and hypothalamic gene expression in the leopard frog (Rana pipiens).

Abstract

We assessed octylphenol (OP), an estrogenic endocrine-disrupting chemical, and UV-B radiation, a known stressor in amphibian development, for their effects on hypothalamic gene expression and premetamorphic development in the leopard frog Rana pipiens. Newly hatched tadpoles were exposed for 10 days to OP alone at two different dose levels; to subambient UV-B radiation alone; and to two combinations of OP and UV-B. Control animals were exposed to ethanol vehicle (0.01%) exposure, a subset of tadpoles from each treatment group was raised to metamorphosis to assess differences in body weight and time required for hindlimb emergence. Tadpoles from one of the OP/UV-B combination groups had greater body weight and earlier hindlimb emergence (p < 0.05), but neither OP nor UV-B alone produced significant changes in body weight or hindlimb emergence, indicating a potential mechanism of interaction between OP and UV-B. We hypothesized that the developing hypothalamus might be a potential environmental sensor for neurotoxicologic studies because of its role in the endocrine control of metamorphosis. We used a differential display strategy to identify candidate genes differentially expressed in the hypothalamic region of the exposed tadpoles. Homology cloning was performed to obtain R. pipiens glutamate decarboxylases--GAD65 and GAD67, enzymes involved in the synthesis of the neurotransmitter gamma-aminobutyric acid (GABA). cDNA expression profiles revealed that OP and UV-B affected the levels of several candidate transcripts in tadpole (i.e., Nck, Ash, and phospholipase C gamma-binding protein 4 and brain angiogenesis inhibitor-3) and metamorph (i.e., GAD67, cytochrome C oxidase, and brain angiogenesis inhibitor-2 and -3) brains. This study represents a novel approach in toxicology that combines physiologic and molecular end points and indicates that levels of OP commonly found in the environment and subambient levels of UV-B alter the expression of important hypothalamic genes and disrupt tadpole growth patterns.

Assessment of Estrogenic Endocrine-Disrupting Chemical Actions in the Brain Using in Vivo Somatic Gene Transfer

“…Previous work from our laboratory demonstrated that environmentally relevant levels of the estrogenic pollutant octylphenol modulates the expression of multiple hypothalamic genes in leopard frog tadpoles (Crump et al 2002) and in hatchling snapping turtles (Trudeau et al 2002). In the latter study, differential display PCR was used, and it is not known if the affected transcripts were directly or indirectly regulated by 4- t -octylphenol or E 2 .…”

Global Increases in Ultraviolet B Radiation: Potential Impacts on Amphibian Development and Metamorphosis

“…Interactions may also occur between UVBR and contaminants, when one factor enhances the toxicity of the other factor (Blaustein et al 2001). Other recent studies on amphibians have demonstrated that interactions between UVBR and various stressors-including (1) low genetic diversity (Weyrauch and Grubb 2006), (2) sodium nitrite (Macías et al 2007), (3) bisphenol A (Koponen and Kukkonen 2002), (4) fire-retardant chemicals , (5) octylphenol (Crump et al 2002;Croteau et al 2008), and (6) copper chloride (Baud and Beck 2005)-produce adverse effects in exposed amphibians (Table 1). In recent years, UVBR levels have increased dramatically in some aquatic environments, whereas levels in other water systems have moderately or scarcely changed because of high DOC levels.…”

“…The actual mechanism by which UVBR disrupts amphibian development remains to be elucidated. Crump et al (2002) hypothesized that the developing hypothalamus might be a potential environmental sensor for neurotoxicologic studies because of its role in the endocrine control of metamorphosis. They demonstrated that a 10-d exposure of R. pipiens tadpoles to subambient levels of UVBR (7 mW/cm 2 , with or without the chemical 4-octylphenol) altered the expression of important hypothalamic genes (e.g., glutamate decarboxylase 67) at metamorphic climax as well as genes in the tadpole diencephalon Figure 2.…”

Persistent polar depletion of stratospheric ozone and emergent mechanisms of ultraviolet radiation-mediated health dysregulation

“…At the organismal level for aquatic and terrestrial species, both plants and animals are at risk, and the most pronounced physiological alterations induced by excessive UVR exposure are the production of reactive oxygen species (ROS) (6, 7, 8), DNA mutations (6), and elevated carcinogenicity (9, 10). Gene expression can be altered by UVR in both plants (7, 11, 12) and animals (13). Overall, from a life history standpoint, any UVR mediated biochemical or physiological alteration has the potential to reduce individual fitness, thereby leading to reduced populations and negatively impacting ecological integrity.…”