All-trans-retinoic acid
IUPAC name	(2E,4E,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohexen-1-yl)nona-2,4,6,8-tetraenoic acid
Other names	vitamin A acid; RA
Identifiers
CAS number	302-79-4 Y
PubChem	444795
SMILES	CC1=C(C(CCC1)(C)C)/C=C/C(=C/C=C/C(=C/C(=O)O)/C)/C
Properties
Molecular formula	C20H28O2
Molar mass	300.43512 g/mol
Appearance	yellow to light orange crystalline powder with characteristic floral odor [1]
Melting point	180-182 °C, crystals from ethanol [1]
Solubility in water	nearly insoluble
Solubility in fat	soluble
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Retinoic acid is the oxidized form of Vitamin A, with only partial vitamin A function. It functions in determining position along embryonic anterior/posterior axis in chordates. It acts through Hox genes, which ultimately control anterior/posterior patterning in early developmental stages. ^[2] Retinoic acid acts by binding to heterodimers of the retinoic acid receptor (RAR) and the retinoid X receptor (RXR), which then bind to retinoic acid response elements (RAREs) in the regulatory regions of direct targets (including Hox genes), thereby activating gene transcription. Retinoic acid receptors mediate transcription of different sets of genes of cell differentiation, thus it also depends on the target cells. One of the target genes is the gene of the retinoic acid receptor itself which occurs during positive regulation.^[3]. Control of retinoic acid levels is maintained by a suite of proteins.^[2]

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, 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.^[4]

[edit] Biological activity

Retinoic acid can be produced by oxidation in the body from either retinal or retinol, but once produced, cannot be reduced again.

Retinoic acid is responsible for all of the activity of vitamin A, save visual pigment effects which require retinal (retinaldehyde), and for effects which require retinol in both the male and female reproductive tracts. Thus, if animals are fed only retinoic acid but no vitamin A (retinol or retinal), they suffer none of the growth-stunting or epithelial-damaging effects of lack of vitamin A (including no xerophthalmia-- dryness of the cornea), but they do suffer retina degeneration and blindness, due to pure retinal (retinaldehyde) deficiency. Vitamin A-deprived but retinoic acid supplemented male rats exhibit hypogonadism and infertility; similar treatment of female rats causes infertility due to fetal resorption ^[5]

[edit] References