biology

Neurotrophin-3

Neurotrophin-3 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 Neurotrophin-3 rather than just read about it. In short: Neurotrophin-3 is a protein that in humans is encoded by the NTF3 gene. The protein encoded by this gene, NT-3, is a neurotrophic factor in the NGF (Nerve Growth Factor) family of neurotrophins.

Key takeaways

Neurotrophin-3 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Neurotrophin-3 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Neurotrophin-3 from memory before moving on to harder problems.

Reference excerpt

Neurotrophin-3 is a protein that in humans is encoded by the NTF3 gene. The protein encoded by this gene, NT-3, is a neurotrophic factor in the NGF (Nerve Growth Factor) family of neurotrophins. It is a protein growth factor which has activity on certain neurons of the peripheral and central nervous system; it helps to support the survival and differentiation of existing neurons, and encourages the growth and differentiation of new neurons and synapses. NT-3 was the third neurotrophic factor to be characterized, after nerve growth factor (NGF) and BDNF (Brain Derived Neurotrophic Factor).

Function Although the vast majority of neurons in the mammalian brain are formed prenatally, parts of the adult brain retain the ability to grow new neurons from neural stem cells; a process known as neurogenesis. Neurotrophins are chemicals that help to stimulate and control neurogenesis. NT-3 is unique in the number of neurons it can potentially stimulate, given its ability to activate two of the receptor tyrosine kinase neurotrophin receptors (TrkC and TrkB). Mice born without the ability to make NT-3 have loss of proprioceptive and subsets of mechanoreceptive sensory neurons.

Mechanism of action NT-3 binds three receptors on the surface of cells which are capable of responding to this growth factor:

TrkC (pronounced "Track C"), is apparently the "physiologic" receptor, in that it binds with greatest affinity to NT-3. However, NT-3 is capable of binding and signaling through a TrkC-related receptors called TrkB. Finally, NT-3 also binds a second-receptor type besides Trk receptors, called the LNGFR (for "low affinity nerve growth factor receptor).

High affinity receptors TrkC is a receptor tyrosine kinase (meaning it mediates its actions by causing the addition of phosphate molecules on certain tyrosines in the cell, activating cellular signaling). As mentioned above, there are other related Trk receptors, TrkA and TrkB. Also as mentioned, there are other neurotrophic factors structurally related to NT-3:

NGF (for "Nerve Growth Factor") BDNF (for "Brain Derived Neurotrophic Factor") NT-4 (for "Neurotrophin-4") While TrkB mediates the effects of BDNF, NT-4, and NT-3, TrkA binds and is activated by NGF, and TrkC binds and is activated only by NT-3.

Low affinity receptors The other NT-3 receptor, the LNGFR, plays a somewhat less clear role. Some researchers have shown the LNGFR binds and serves as a "sink" for neurotrophins. The crystal structure of NT-3 shows that NT-3 forms a central homodimer around which two glycosylated p75 LNGFR molecules bind symmetrically. The symmetrical binding takes place along the NT-3 interfaces, resulting in a 2:2 ligand-receptor cluster in the center. Cells which express both the LNGFR and the Trk receptors might therefore have a greater activity – since they have a higher "microconcentration" of the neurotrophin. It has also been shown, however, that the LNGFR may signal a cell to die via apoptosis – so therefore cells expressing the LNGFR in the absence of Trk receptors may die rather than live in the presence of a neurotrophin.

See also Tropomyosin receptor kinase B § Agonists

References

Illustrations

Worked examples

Example 1 — a first encounter with Neurotrophin-3

Start with the simplest possible case. Write down what Neurotrophin-3 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 Neurotrophin-3 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 Neurotrophin-3 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 Neurotrophin-3

In research: Neurotrophin-3 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 Neurotrophin-3 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: Neurotrophin-3 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Developmental neuroscience, Genes on human chromosome 12, Growth factors, so understanding it makes those chapters shorter.
In everyday life: Look for Neurotrophin-3 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 Neurotrophin-3 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Neurotrophin-3 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 Neurotrophin-3 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Neurotrophin-3 in simple terms?

Neurotrophin-3 is a protein that in humans is encoded by the NTF3 gene. The protein encoded by this gene, NT-3, is a neurotrophic factor in the NGF (Nerve Growth Factor) family of neurotrophins.

Why does Neurotrophin-3 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 Neurotrophin-3?

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 Neurotrophin-3.