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FBJ murine osteosarcoma viral oncogene homolog B, also known as FOSB or FosB, is a protein that, in humans, is encoded by the ''FOSB'' gene.〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=2354 )〕 The FOS gene family consists of 4 members: FOS, FOSB, FOSL1, and FOSL2. These genes encode leucine zipper proteins that can dimerize with proteins of the JUN family (e.g., c-Jun, JunD), thereby forming the transcription factor complex AP-1. As such, the FOS proteins have been implicated as regulators of cell proliferation, differentiation, and transformation.〔 FosB and its truncated splice variants ΔFosB and (further truncated) Δ2ΔFosB are all involved in osteosclerosis, even though Δ2ΔFosB lacks a known transactivation domain, preventing it from affecting gene transcription through the AP-1 complex. The ΔFosB splice variant has been identified as playing a central, ''crucial'' (necessary and sufficient)〔〔 role in the development and maintenance of pathological behavior and neural plasticity involved in both behavioral addictions (associated with natural rewards) and drug addictions.〔〔 E.g., ΔFosB overexpression causes the development addiction-related structural neuroplasticity to occur throughout the reward system. ΔFosB differs from the full length FosB and further truncated Δ2ΔFosB in its capacity to produce these effects, as only accumbal ΔFosB overexpression is associated with pathological responses to drugs. ==ΔFosB== ΔFosB or Delta FosB is a truncated splice variant of FosB. ΔFosB has been implicated as a critical factor in the development of virtually all forms of behavioral and drug addictions.〔〔〔 In the brain's reward system, it is linked to changes in a number of other gene products, such as CREB and sirtuins.〔 In the body, ΔFosB regulates the commitment of mesenchymal precursor cells to the adipocyte or osteoblast lineage. In the nucleus accumbens, ΔFosB functions as a "sustained molecular switch" and "master control protein" in the development of an addiction.〔〔〔 In other words, once "turned on" (sufficiently overexpressed) ΔFosB triggers a series of transcription events that ultimately produce an addictive state (i.e., compulsive reward-seeking involving a particular stimulus); this state is sustained for months after cessation of drug use due to the abnormal and exceptionally long half-life of ΔFosB isoforms.〔〔〔 ΔFosB expression in D1-type nucleus accumbens medium spiny neurons directly and positively regulates drug self-administration and reward sensitization through positive reinforcement while decreasing sensitivity to aversion.〔〔 Based upon the accumulated evidence, a medical review from late 2014 argued that accumbal ΔFosB expression can be used as an addiction biomarker and that the degree of accumbal ΔFosB induction by a drug is a metric for how addictive it is relative to others.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「FOSB」の詳細全文を読む スポンサード リンク
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