Caltech Professor Mikhail Shapiro has overcome one of the main limitations to using “reporter genes,” markers that help researchers get a sense for what cells are doing. Because light does not penetrate well through most living tissue, the commonly used green fluorescent protein cannot be used for monitoring the activity of cells deep inside an organism. Shapiro’s team has developed a new reporter gene that allows them to see genetic activity using ultrasound, which can penetrate deeply through tissue.