Reporter gene assays are laboratory techniques used to study gene expression. They involve inserting a gene that encodes a measurable protein, known as a reporter gene, into a cell or organism. Common reporter genes include luciferase and GFP (green fluorescent protein), which produce light or fluorescence, allowing researchers to easily track and quantify gene activity. These assays help scientists understand how genes are regulated and how they respond to various stimuli. By measuring the activity of the reporter gene, researchers can gain insights into cellular processes, such as signal transduction and gene regulation, in both basic research and drug development.