c-Fos

c-Fos is an immediate-early gene product and transcription factor that functions as a central mediator of stimulus-dependent gene expression, linking transient extracellular signals to long-term cellular responses through regulation of downstream target genes^[1]. Mechanistically, c-Fos belongs to the Fos family and forms the activator protein-1 (AP-1) transcription factor complex through dimerization with Jun family proteins, thereby regulating genes involved in cellular differentiation, proliferation, development, plasticity, and survival^[4][3][2]. c-Fos expression is rapidly induced by neuronal activity, calcium- and cAMP-dependent signaling, and other environmental stimuli, making it a widely used molecular marker of cellular activation and stimulus-transcription coupling in experimental systems^[1][3]. In disease and experimental models, c-Fos has been extensively employed to map activated neuronal populations during seizures, learning, memory formation, and behavioral responses, providing a framework for investigating neural circuit function and activity-dependent transcriptional programs^[1][3]. Compared with related Fos family members, including FosB, Fra-1 (FOSL1), and Fra-2 (FOSL2), c-Fos contains a C-terminal transactivation domain and exhibits distinctive transcriptional regulatory properties within AP-1 complexes^[4]. For experimental applications, c-Fos is primarily used as an activity-dependent biomarker rather than a direct pharmacological target, enabling quantitative assessment of cellular activation, neural network recruitment, and stimulus-responsive signaling pathways in neuroscience and molecular biology research^[3][5].