text: Activity-regulated cytoskeleton-associated protein is a plasticity protein that in humans is encoded by the ARC gene. The gene is believed to derive from a retrotransposon. The protein is found in the neurons of tetrapods and other animals where it can form virus-like capsids that transport RNA between neurons.
  ARC mRNA is localized to activated synaptic sites in an NMDA receptor-dependent manner, where the newly translated protein is believed to play a critical role in learning and memory-related molecular processes. Arc protein is widely considered to be important in neurobiology because of its activity regulation, localization, and utility as a marker for plastic changes in the brain. Dysfunction in the production of Arc protein has been implicated as an important factor in understanding various neurological conditions, including amnesia, Alzheimer's disease, Autism spectrum disorders, and Fragile X syndrome. 
  ARC was first characterized in 1995 and is a member of the immediate-early gene (IEG) family, a rapidly activated class of genes functionally defined by their ability to be transcribed in the presence of protein synthesis inhibitors. Along with other IEGs such as ZNF268 and HOMER1, ARC is a significant tool for systems neuroscience as illustrated by the development of the cellular compartment analysis of temporal activity by fluorescence in situ hybridization, or catFISH technique (see fluorescent in situ hybridization).