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Photo of Megan McClean and Stephanie Geller

Shining bright: McClean earns young innovator honor for optogenetics advance

Written By: Tom Ziemer



University of Wisconsin-Madison biomedical engineers are illuminating the path toward improved treatments for fungal infections through a new tool that uses light to control gene expression in yeast cells.

Assistant Professor Megan McClean and graduate student Stephanie Geller worked with collaborators at the University of Freiburg in Germany to generate a light-controllable repressor of gene expression in Saccharomyces cerevisiae, a species of yeast used in baking and brewing.

McClean and Geller outline their approach in a new paper that’s part of a special young innovators issue of the journal Cellular and Molecular Bioengineering (CMBE). As one of 12 CMBE Young Innovators, McClean will receive an award and present her work during a special session at the Biomedical Engineering Society’s annual meeting in October 2019 in Philadelphia.

The group’s approach uses a mutated version of the same protein—Cas9—as the popular gene editing tool CRISPR, but it’s unable to cut the genome or enter the nucleus of a cell on its own. McClean and Geller are able to localize the modified Cas9 protein to the nucleus using LINuS, an optogenetic tool developed in the lab of collaborator Barbara Di Ventura.

 Stephanie Geller
PhD student Stephanie Geller has been working on the project since starting as a research intern in McClean’s lab. 

By co-expressing the modified Cas9 protein with a specific guide RNA, researchers can target a particular gene to repress. It’s an extension of the McClean lab’s work in optogenetics, which employs light to regulate processes in cells and tissues.

Now that they’ve built and tested the tool on a simpler model yeast species, the researchers plan to use it in pathogenic yeasts as part of McClean’s ongoing work to uncover new drug targets for fungal infections. Fungal cells can be tricky to specifically target because their cellular components and structures are very similar to those in human cells.

“Fungal infections are pretty scary, particularly as immunocompromised populations grow, and there is really a limited number of drugs to target fungi,” McClean says. “They’re so close to human cells. So what can you target that won’t make people sick? There are four classes of drugs, and when you only have four classes of drugs, you start to see drug resistance as they’re used more and more. So to get out ahead of that, what is specific to fungi that one could target to alleviate or prophylactically suppress fungal infections?”

Geller, a third-year PhD student, is particularly interested in using the new approach to study the yeast Candida albicans, the culprit behind fungal infections such as oral thrush and vaginal yeast infections. The pathogenic yeast can also form biofilms on medical devices, such as catheters, and then disperse into the bloodstream, causing devastating systemic illnesses.

McClean notes that while researchers have decoded many of the mechanisms behind biofilm formation, the dispersal process remains a mystery.

“If you can understand the process, you can start trying to find druggable targets,” says Geller, who plans to examine how altering gene expression affects dispersion.

The paper is the product of four years of hard work, dating back to when Geller started as a research intern in McClean’s lab.

“The ability to spatiotemporally control gene expression with light is new and exciting,” says McClean, “and for being able to ask medically relevant questions in complex pathogenic microbial communities like biofilms, it’s a really important tool the biomedical engineering community needs.”