By Liting Chen
Before I started my internship here at Duke two months ago, when I thought of fish, I imagined little bubbling creatures swimming around, perhaps with background music from Finding Nemo. But after spending time working on Project 3 (Developmental PAH Exposures in Fish: Mechanisms of Toxicity, Adaptation, and Later Life Consequences) in Dr. Di Giulio’s lab with the help of my mentor Daniel Brown, I’ve gained more insights into how the development of killifish (Fundulus heteroclitus) is closely related to environment health.
The goal of Project 3 is to evaluate how early life exposure to PAHs (polycyclic aromatic hydrocarbons) can affect later life development and performance of killifish. The project focuses on the Superfund Site located on the Elizabeth River in Virginia at the Atlantic Wood Industries, where the water is heavily polluted by PAHs via former wood treatment. Exposure to high concentrations of certain PAHs can cause severe heart defects to killifish from uncontaminated rivers (in this project – the King’s Creek site). However, it has been found that killifish from the Atlantic Wood site are resistant to the effects of PAHs and do not show cardiovascular defects. It remains uncertain whether there are developmental or health problems associated with this resistance as a trade-off (i.e. tolerance to thermal stress, swimming speed, etc.).
To better understand heart defects in fish, I exposed some fish embryos collected from the King’s Creek population to a sediment extract from the Elizabeth River. After being stored in the incubator for one day, the embryos were screened under the scope and the ones with developed body axis were divided into different groups and dosed at different Elizabeth River Sediment Extract (ERSE) concentration levels. After 144 hours, the observation under the scope showed that the control group developed healthy, well functioning hearts, and the group with a lower dosage showed misaligned hearts which restricted normal blood flow, while the group that had embryos dosed at a high ERSE concentration were found with “stringy hearts” or “tube hearts” that couldn’t pump blood effectively.
In order to look at the potential “costs” made by killifish from the Atlantic Wood site to gain PAH resistance, we also measured the area of tattered tailfins observed in fish from the contaminated site and compared that with the tailfin of fish from King’s Creek to see how it might affect their swimming performance. For both King’s Creek and Atlantic Wood populations, we collected 6 fish from each of the following treatment groups: control, 0.1% ERSE, and 1.0% ERSE group. Each fish was mounted on a piece of wax with its tail fanned and pinned to the wax. While there was a noticeable difference observed of the tailfin area between these two populations, we are still under the process of making more precise measurements.
Besides the physical difference observed between these two populations, we are also looking to see if there’s any difference in gene expression specifically for the gene “nebulette”, which is essential for cardiac muscle contraction. While we are still on the way of validating primers for nebulette, I’m looking forward to finding out if there’s a difference in expression of nebulette between fish from the Atlantic Wood and the reference site, and perhaps connecting that to the observed cardiovascular problems mentioned before.
While I’m excited to find out how early life exposures can affect later life consequences of fish, I’m also lucky enough to get early life exposures to such an enriching research experience and get to know these wonderful scientists in the lab. And I know without a doubt that this will exert a great later life consequence on me too!