Developmental manipulation of estrogen signaling alters adult visual function - Visual system development is a highly complex process involving coordination of environmental cues, cell
signals, and integration of functional circuits. Consequently, a change to any step, due to a mutation or
chemical exposure, can lead to deleterious consequences. One class of chemicals known to have both overt and
subtle effects on the visual system is endocrine disrupting compounds (EDCs). EDCs are environmental
contaminants; most target estrogen signaling by either preventing estrogen synthesis or binding to estrogen
receptors. Developmental disruption of estrogen synthesis in animal models causes apoptotic cell death,
thinning in retina and cornea, and abnormal and delayed eye growth, indicating estrogen signaling is critical
for proper development. Estrogen also maintains eye function: age-related changes in estrogen levels are
associated with neurodegenerative retinal diseases and estrogen modulation as a clinical treatment for breast
cancer leads to vision related complications. Unfortunately, we know very little about the mechanisms and
long-term impact of abnormal estrogenic signaling on visual sensation and perception. We propose to use
zebrafish to address this by directly manipulating estrogenic pathways during constrained periods of visual
system development and examining the functional impact on adult retinal anatomy, physiology, and visually
guided behaviors. Uniquely, we will compare the effects of two well-known, environmentally relevant
compounds, tributyltin (TBT), an estrogen synthesis (aromatase) inhibitor, and bisphenol A (BPA), an estrogen
agonist, with the effects of 4-OH-A, a standard inhibitor and cancer treatment drug, and estradiol, the
biologically relevant estrogen. Zebrafish (Danio rerio) is the ideal animal model for this study: retinal anatomy
is similar to humans, sensory development depends on estrogen signaling, and aromatase and estrogen
receptor expression patterns have been well categorized; developmental timing of eye and retina,
categorization of vision based behaviors, and physiological responses have also been documented. Our central
hypothesis is that developmental manipulation of estrogen signaling will target specific retinal cell types
causing functional deficits in vision physiology and behavior in adult animals. We will test this hypothesis by
first confirming compound efficacy and mechanism of action ex vivo using whole brain homogenates (Aim. 1.1)
and in vivo by direct uptake of compounds via tank water (Aim 1.2). We will then screen for behavioral (Aim
2.1) and physiological (Aim 2.2) changes to the adult zebrafish visual system followed by more detailed patch
clamp (Aim 3.1) and histological (Aim 3.2) analyses to identify which retinal cells/circuits are compromised by
compound exposure. The expected results are relevant to diseases that involve retinal/visual disruptions, to
studies in which therapeutic agents target the endocrine system, and to further examination of mechanisms
underlying EDC-associated changes in neuronal function, perception, and/or behavior resulting from aberrant
estrogen signaling.
