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|Section2= |Section7= |Section8= }} Retinoic acid is a metabolite of vitamin A (retinol) that mediates the functions of vitamin A required for growth and development. Retinoic acid is required in chordate animals, which includes all higher animals from fish to humans. During early embryonic development, retinoic acid generated in a specific region of the embryo helps determine position along the embryonic anterior/posterior axis by serving as an intercellular signaling molecule that guides development of the posterior portion of the embryo. It acts through Hox genes, which ultimately control anterior/posterior patterning in early developmental stages. The key role of retinoic acid in embryonic development mediates the high teratogenicity of retinoid pharmaceuticals, such as isotretinoin used for treatment of cancer and acne. Oral megadoses of pre-formed vitamin A (retinyl palmitate), and retinoic acid itself, also have teratogenic potential by this same mechanism. == Mechanism of biological action == Retinoic acid acts by binding to the retinoic acid receptor (RAR), which is bound to DNA as a heterodimer with the retinoid X receptor (RXR) in regions called retinoic acid response elements (RAREs). Binding of the retinoic acid ligand to RAR alters the conformation of the RAR, which affects the binding of other proteins that either induce or repress transcription of a nearby gene (including Hox genes and several other target genes). Retinoic acid receptors mediate transcription of different sets of genes controlling differentiation of a variety of cell types, thus the target genes regulated depend upon the target cells.〔(Venkatesh K, Srikanth L, Vengamma B, Chandrasekhar C, Sanjeevkumar A, Mouleshwara Prasad BC, Sarma PV. In vitro differentiation of cultured human CD34+ cells into astrocytes. Neurol India 2013;61:383-8 )〕 In some cells, one of the target genes is the gene for the retinoic acid receptor itself (RAR-beta in mammals), which amplifies the response. Control of retinoic acid levels is maintained by a suite of proteins that control synthesis and degradation of retinoic acid.〔〔 The molecular basis for the interaction between retinoic acid and the Hox genes has been studied by using deletion analysis in transgenic mice carrying constructs of lacZ reporter genes. Such studies have identified functional RAREs within flanking sequences of some of the most 3' Hox genes (including Hoxa1, Hoxb1, Hoxb4, Hoxd4), suggesting a direct interaction between the genes and retinoic acid. These types of studies strongly support the normal roles of retinoids in patterning vertebrate embryogenesis through the Hox genes.〔 〕 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「retinoic acid」の詳細全文を読む スポンサード リンク
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