Table 1.

Tissue distributions of RARs and RXRs in mammals, and phenotypes of isotype-specific knockout in mouse.

Receptor (gene symbol)	Expression pattern		Knockout phenotype		Ref
	Most abundant	Liver	General	Liver specific
RARα (NR1B1)	Widely expressed	Parenchyma, endothelia, kupffer and stellate cell	Postnatal lethality and some abnormalities including testis degeneration		[16-21]
RARβ (NR1B2)	Lung, intestine, genitalia, epithelia, limbs, brain.	Parenchyma, endothelial, Kupffer and stellate cell	No obvious external and internal abnormalities		[19,22-24]
PARγ (NR1B3)	Cartilage, embryo, epidermis, skeleton	Parenchyma, endothelial, Kupffer and stellate cell	Postpartum lethality and growth deficiency. (male sterility; Agenesis of the ocular Harderian gland and homeotic transformations of the axial skeleton)		[19,25-27]
RXRα (NR2B1)	Liver, kidney, spleen, placenta, epidermis and a variety of visceral tissues	Parenchyma, endothelial, kupffer and stellate cell	Died in utero and displayed myocardial and ocular malformations	Disturbed lipid metabolism; a deficiency of Epo expression in the fetal liver; impaired regenerative capacity	[19,28-30]
RXRβ (NR2B2)	Widely expressed	Parenchyma, endothelial, Kupffer and stellate cell	Normal. Except male infertility.		[19,30-32]
RXRγ (NR2B3)	Muscle, brain	Parenchyma, endothelial, and Kupffer cell	Postnatal lethality and some abnormalities including homeotic transformation		[19,27,32,33]

Note: The expression levels of all RXR subtypes is higher than all RAR subtypes in all liver cells.