Transparent Zebrafish Used as Digestion Models


Steve Farber, faculty member at Thomas Jefferson University in Philadelphia and the creator of BioEYES, came to St. Mary’s on Nov. 2 as part of the Natural Science and Mathematics (NS&M) Colloquium Series.

One of Farber’s focuses was his outreach program BioEYES, which brings zebrafish into elementary school classrooms for children to experiment with. The weeklong program helps students learn about science but also encourages learning about sex, gender stereotypes, and race through interactions with the mating fish. BioEYES grew out of an activity during a university Bring Your Child to Work Day and has become an international program that has reached 50,000 students.

In the program, the students are able to mate two zebrafish and watch the resulting eggs grow and develop. Thirty hours after the eggs are laid by the female, the students are able to see the hearts of the developing fish beating. Full development happens in two-and-a-half days. The way that the zebrafish develops allows the observer to see right through the fish at each stage of development.

The research Farber does in his lab uses zebrafish because of their rapid development, the fact that they are so hardy, and the fact that they can produce 1,000 offspring weekly. Several years ago, when Farber was applying for grants involving animal research, the main question he wanted to answer was how his research was relevant to humans. Today, however, this question has all but disappeared with the understanding that a large percentage of the DNA in animals is the same as in humans. In zebrafish, 93 percent of the mitochondrial DNA is the same as in humans.

Before scientists sequenced entire genomes, it was generally believed that the smarter, more complex organisms would have more genes. While zebrafish do have three times less DNA than humans do, they have 25 chromosomes as compared to our 23. These differences show the progress of evolution both species have undergone in the 350 million years since a common ancestor. Farber likened genes to the periodic table. The difference between a frog, a duck, and a human is not what they are made out of but how they are built. One can switch out genes between them and they still might function. This is considered unethical to do with humans, but can be done with other animals.

But why study the digestion, specifically fat metabolism? According to Farber, the average American is 23 pounds overweight. “We as a society are really getting sick, and I keep waiting to see how sick we need to get before we change the game.” This creates an enormous economic burden on the society, an effect that isn’t reflected in the prices of the foods we put into our bodies.

“The poor health in our country is directly related to the nutritionally poor food we eat. Given this sad fact, it is imperative to firmly understand the physiological mechanism of lipid catabolism, absorption, and transportation within the human body,” says senior Luke Trout.

Farber takes advantage of the fact that the zebrafish are mostly transparent to look at their intestines. He puts the fish in a mixture of water and egg yolk, and then places the tank on a rocker so that the fish are forced to gulp the fatty water. Fluorescent markers added to the egg yokes begin to glow once broken down into fatty acids. The fact that Farber can watch this process of absorption happening is a big advantage over other methods of observation which can take days, by which point the cells being observed are no longer as viable. “What really impressed me about this particular research project is that it combined a lot of different disciplines, using fluorescently tagged fatty acids to track the [fish] metabolism in real time invivo,” said senior Kathy Michels.

What has been observed is that fatty acids go into lipid droplets, and cholesterol into endosomes. Farber says that this is interesting, but what is more exciting is the observation that if cholesterol is only in water, it is not absorbed by the intestines. But, if it is combined with the egg, it is. Farber hypothesized that this is because when the fats are broken down into fatty acids that the cells attempt to absorb, the cells also take in the cholesterol.