Unlikely as it might have seemed, the bundling protein proved to be the key to the team’s discovery of Hirano bodies in the slime mold. Hirano bodies, it turns out, are partially made of actin; a piece of the actin bundling protein triggers cells to make Hirano bodies.

“I was studying the 34 kDa actin bundling protein and I wanted to know how it got where it needed to go in the cell to form the structures for locomotion and eating,” said Maselli, a former UGA doctoral student who is now an assistant professor at Chicago State University.

Other scientists already had demonstrated the bundling protein’s role in making structures that enable cell movement and feeding, Maselli said. But no one had looked at how the protein “knew” to go help form those structures.

Figuring out how a protein like this one works is like figuring out how a clock works: Remove a piece from the clock, tinker with it a bit, put it back in and see what happens.

Maselli took the gene for the bundling protein, removed bits from it, put it back in the slime mold and watched to see what happened. He suspected that calcium helped control the protein’s travels in the cell so he removed the bits that interacted with calcium.

In the slime mold cells with the altered bundling protein, Maselli and colleagues observed large, almond-shaped areas packed with parallel filaments. Nothing like this had ever been seen in a slime mold.

Maselli credits Fechheimer with recognizing that these strange bodies resembled the Hirano bodies previously described in brain tissue. The team set out to confirm Fechheimer’s hunch.

When the researchers examined the mysterious structures with an electron microscope, they discovered a match with Hirano bodies’ characteristics. Filament width and spacing, the pattern that filaments formed and the overall shape of the body all checked out, said doctoral student Rich Davis.

Next, the researchers used antibodies that “recognize” specific proteins and showed that the alleged Hirano bodies were made of actin and a handful of other proteins. Finally, Davis inserted the altered gene into mammalian nerve cells and fibroblasts growing in the lab, and the same structure formed in them.