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Retinoic acid
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<p>Retinoic acid (simplified nomenclature for all-<i>trans</i>-retinoic acid) is a <a href="/facts/Metabolite/nAyywVtA">metabolite</a> of <a href="/facts/Vitamin_A/5ewDf9LF">vitamin A</a>1 (all-<i>trans</i>-<a href="/facts/Retinol/pUwofb2S">retinol</a>) that is required for embryonic development, male fertility, regulation of bone growth and immune function. All-<i>trans</i>-retinoic acid is required for <a href="/facts/Chordate/AldL6ARm">chordate</a> animal development, which includes all higher animals from fish to humans. During early <a href="/facts/Embryonic_development/1lFY4EoW">embryonic development</a>, all-<i>trans</i>-retinoic acid generated in a specific region of the embryo helps determine position along the embryonic anterior/posterior axis by serving as an <a href="/facts/Intercellular_signaling/6oYAVP9I">intercellular signaling</a> molecule that guides development of the posterior portion of the embryo. It acts through <a href="/facts/Hox_gene/kP1yVyDY">Hox genes</a>, which ultimately control anterior/posterior patterning in early developmental stages. In adult tissues, the activity of endogenous retinoic acid appears limited to immune function and male fertility. </p><p>All-<i>trans</i>-retinoic acid is the major occurring retinoic acid, while isomers like 13-<i>cis</i>- and 9-<i>cis</i>-retinoic acid are also present in much lower levels. </p><p>The key role of all-<i>trans</i>-retinoic acid in embryonic development mediates the high <a href="/facts/Teratogenicity/j4BN6lsB">teratogenicity</a> of retinoid pharmaceuticals, such as <a href="/facts/Isotretinoin/XBKv4fQJ">isotretinoin</a> (13-<i>cis</i>-retinoic acid) used for treatment of <a href="/facts/Acne/TKJxhHSd">acne</a> or <a href="/facts/Retinol/pUwofb2S">retinol</a> used for skin disorders. High oral doses of preformed vitamin A (<a href="/facts/Retinyl_palmitate/Lo4ebazz">retinyl palmitate</a>), and all-<i>trans</i>-retinoic acid itself, also have teratogenic potential by this same mechanism. </p>