Fall 2008

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Human Vision Seen Through Mollusk Model

Jeanne Serb's research uses mollusks as models for understanding human health issues like macular degeneration, the leading cause of blindness worldwide.

Jeanne Serb has nothing against vertebrates, but she'll never work with them again.

"Invertebrates are much more complex and beautiful. And such strange behaviors. Can I show you a movie?" Serb turns to her computer and plays a clip of scallops flitting back and forth in murky water. "Look how they clap their shells as they move. They remind me of those novelty wind-up teeth that walk. They really book. I love mollusks."

She used to love vertebrates. As a master's student at the University of Illinois, Serb studied turtles. She hoped to earn her Ph.D. with turtles. Turns out, few funding agencies love turtles.

"That's why I switched to mollusks," says Serb, an evolutionary biologist and assistant professor of ecology, evolution and organismal biology. Research funds are available because mollusks are great models for understanding human health issues like eye diseases. With mollusks, she earned her Ph.D. at the University of Alabama.

At Iowa State, Serb is funded by the National Science Foundation to study how complex traits like the eye evolved in scallops. What she learns may shed light, literally, on our understanding of the human eye.

"The scallop eye is a unique model to study eye formation and evolution," Serb says. "Scallops have an image-forming retina and two kinds of photoreceptors, the cells that change light into chemical reactions that inform the brain. If a scallop loses an eye, it regenerates it. That's an exciting prospect that could directly inform how we look at human vision problems."

But why do scallops even have eyes? Most bivalves don't, Serb says. But scallops have a hundred gorgeous peepers. An extreme closeup of the rim of a scallop shell looks like a Salavador Dali painting. The eyes look like a series of giant blue olives balanced on a mountain range.

It's mysteries like scallop eyes that drive Serb's research to go back to the genetic beginnings and parse out how complex traits were assembled and then began to differentiate among species.

"There are genetic mechanisms, like the eye, that up to a point are common across all animal species. I want to know where the point of differentiation begins that has led to a fly's compound eye, a scallop's 100 blue eyes, the camera-type eyes of a fish or our human pair," Serb says.

In a project supported by ISU's Center for Integrated Animal Genomics, Serb and colleagues in veterinary medicine and computer engineering are comparing the genomes of flies and mice to better understand photoreceptor cells.

When photoreceptor cells fail or die, serious vision diseases result. Retinal degenerative diseases, like macular degeneration, are a leading cause of blindness worldwide. As the U.S. population continues to age, it's estimated that macular degeneration will blind more people than all other retinal diseases combined.

"We're looking for similarities between genes in the fly and mouse genomes to see if we can fill in gaps in our knowledge," Serb says. "It'll help scientists begin thinking about creating or saving the receptors in people who are losing their vision."

Evolution - Nature's Editor

Serb says evolution is like an editor working on drafts. Each subsequent draft leaves behind unneeded words, sentences and paragraphs. "If certain combinations of genes don't work, the editor gets out the red pencil and puts an X through it. Over time, the DNA language that's spared the editor's severity makes up genetic conservation. For me, the eye is a good model to study genetic conservation and use that knowledge for the good of human health."