Assistant Professor Veronica Hinman Takes a Closer Look at Hidden Evolution
January 2, 2008
More than 500 million years ago, sea urchins and starfish diverged from their common ancestor and went down different evolutionary paths to become what they are today. When you look closely at their embryonic development, you’ll notice that both species still develop in very similar ways while growing into distinctly different animals. Look even closer, as Veronica Hinman has, and you’ll find a lot of evolution that is hidden in the nuts and bolts of the genetic processes that control development.
“We know today that most animals have the same homologous genes called the developmental gene toolkit. What makes one animal different from another is not the types of genes they use, but how they use them,” said Hinman, assistant professor of biological sciences. “Think of a house: all houses are made from brick, wood, and mortar. Individual houses are just put together in different ways. Likewise, animals use genes differently or in the same way, which causes the animals themselves to be different morphologically.”
In her latest work published in the Dec. 4 issue of the Proceedings of the National Academy of Sciences, Hinman focused her efforts on a specific network of genes involved in development. She experimentally compared this Gene Regulatory Network (GRN) — a very precise model of how genes interact, how they are interconnected and how they function in development — in sea urchins and starfish. Specifically, she looked at the regulatory interactions around a set of highly conserved connections among genes in a region of a GRN called a “kernel.” Her comparison yielded surprising results.
“We could still see conservation of certain developmental processes, but the sea urchin and the starfish use different genes to perform the same function. In both organisms certain genes were expressed in very similar, or homologous, ways, but the genes that regulate them are different,” said Hinman. “If you just looked at the gene expression patterns, you’d say the expressions are different or the same; you put a lot of stock in that—if it expresses the same, it functions the same. We show that this is not true at all.”
She also discovered that different regions of the GRN evolve at different rates, which may explain what is seen in evolution—certain body parts remain highly conserved and other body parts evolve more rapidly. Her work now provides a molecular explanation for this evolutionary phenomenon.
“There is a lot of speculation about how gene regulatory networks evolve. The sea urchin and starfish are the only systems out there where actual detailed experimental comparisons have been performed. Our latest work is the only example so far that uncovers the nuts and bolts of how GRNs evolve,” said Hinman.