biology

Retinoid X receptor

Retinoid X receptor is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Retinoid X receptor rather than just read about it. In short: The retinoid X receptor (RXR) is an important family of transcription factors that can combine with various nuclear receptors to form a protein dimer, which is often needed for those receptors to perform their functions. It is also a nuclear receptor which is activated by 9-cis retinoic acid, but whether its role as a direct endogenous receptor is important biologically is controversial.

Key takeaways

Retinoid X receptor belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Retinoid X receptor to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Retinoid X receptor from memory before moving on to harder problems.

Reference excerpt

The retinoid X receptor (RXR) is an important family of transcription factors that can combine with various nuclear receptors to form a protein dimer, which is often needed for those receptors to perform their functions. It is also a nuclear receptor which is activated by 9-cis retinoic acid, but whether its role as a direct endogenous receptor is important biologically is controversial. It can also bind to 9-cis-13,14-dihydroretinoic acid, which may be an endogenous mammalian RXR-selective agonist. Bexarotene is the only FDA-approved medication that selectively activates the RXRs while exhibiting negligible activity toward the retinoic acid receptors. There are three retinoic X receptors (RXR): RXR-alpha, RXR-beta, and RXR-gamma, encoded by the RXRA, RXRB, RXRG genes, respectively. RXR heterodimerizes with multiple nuclear receptors including CAR, FXR, LXR, PPAR, PXR, RAR, TR, ER and VDR. RXRs are permissive co-receptors as only one of six alleles is needed for normal development and health. Given this, it is difficult to extrapolate whether the RXR pathway has its own endogenous activity driven by 9-cis retinoic acid species or whether it merely participates in other pathways, predominantly the retinoic nuclear receptor pathway. Genomic knockout of the RXRs results in obesity resistance while bexarotene treatment causes severe hypothyroidism, suggesting that the RXR pathway functions at least to regulate the thyroid hormone receptor pathway.

Pharmacology The retinoid X receptors are selectively targeted by certain pharmaceutical retinoids, in particular as part of cancer treatments or to treat severe hand eczema. These including bexarotene and alitretinoin (synthetic 9-cis-retinoic acid), though with the caveat that alitretinoin also has some affinity for the Retinoic Acid Receptors (RARs).

References

External links Retinoid+X+Receptors at the U.S. National Library of Medicine Medical Subject Headings (MeSH)

Worked examples

Example 1 — a first encounter with Retinoid X receptor

Start with the simplest possible case. Write down what Retinoid X receptor claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Retinoid X receptor before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Retinoid X receptor ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Retinoid X receptor

In research: Retinoid X receptor appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Retinoid X receptor in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Retinoid X receptor is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genes on human chromosome 1, Genes on human chromosome 6, Genes on human chromosome 9, so understanding it makes those chapters shorter.
In everyday life: Look for Retinoid X receptor outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Retinoid X receptor in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Retinoid X receptor means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Retinoid X receptor out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Retinoid X receptor in simple terms?

Why does Retinoid X receptor matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Retinoid X receptor?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Retinoid X receptor.