The Fos gene is a crucial part of the cellular machinery that helps regulate gene expression. It encodes a protein that is involved in various cellular processes, including cell growth, differentiation, and survival. The Fos protein often forms a complex with another protein called Jun, together known as the AP-1 transcription factor, which plays a significant role in responding to external signals. Fos is particularly important in the context of cancer research and neuroscience. Abnormal expression of the Fos gene can lead to uncontrolled cell proliferation, contributing to tumor development. In the brain, Fos is used as a marker for neuronal activity, helping researchers understand how neurons respond to stimuli and participate in learning and memory.