biology

Plexin-A4

Plexin-A4 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 Plexin-A4 rather than just read about it. In short: Plexin-A4 is a protein that in humans is encoded by the PLXNA4 gene. Plexin-A4 functions as a coreceptor for Semaphorin-3A and is involved in nervous system development.

Key takeaways

Plexin-A4 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Plexin-A4 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Plexin-A4 from memory before moving on to harder problems.

Reference excerpt

Plexin-A4 is a protein that in humans is encoded by the PLXNA4 gene. Plexin-A4 functions as a coreceptor for Semaphorin-3A and is involved in nervous system development.

Function Plexin A4 binds to neuropilin 1 (Nrp1) and neuropilin 2 (Nrp2) and transduces signals from Sema3A, Sema6A, and Sema6B. These Nrp-plexin and semaphorin complexes initiate cascades that regulate diverse processes such as axon pruning and repulsion, dendritic attraction and branching, regulation of cell migration, vascular remodeling, and growth cone collapse. Both upregulation and downregulation of Plexin A4 has been observed following neural injury suggesting a dynamic role for Sema3A and Plexin A4 in neural maintenance and regeneration. Additionally, Sema3A and therefore its receptor, Plexin A4, have been implicated as possible components of fast-fatigable muscle fiber denervation in ALS.

Structure Plexin A4 has ~1890 amino acids that include a likely signal sequence, transmembrane domain, and 12 extracellular N-linked glycosylation sites. It also contains domains consistent with other class A plexins including a Sema domain, three "Met-related sequences"/cysteine clusters, three extracellular glycine-proline repeats, intracellular SP domains, and a putative intracellular tyrosine kinase phosphorylation site.

Tissue distribution In the adult rat central nervous system (CNS), plexin A4 was present in neurons and fibers throughout the brain and spinal cord, including neocortex, hippocampus, lateral hypothalamus, red nucleus, facial nucleus, and the mesencephalic trigeminal nucleus. Fibers expressed Plexin A4 in the lateral septum, nucleus accumbens, several thalamic nuclei, substantia nigra pars reticulata, zona incerta, pontine reticular formation, as well as in several cranial nerve nuclei. Plexin A4 has been found in dorsal and, to a greater extent, ventral horns of the spinal cord. Both motor neurons and interneurons in the ventral horn express Plexin A4. Motor axons exiting via the ventral roots and the ascending and descending white matter tracts express Plexin A4. In dorsal root ganglia, Plexin A4 is expressed in the neuronal cell bodies as well as the central and peripheral processes of those cells.

References

Illustrations

Worked examples

Example 1 — a first encounter with Plexin-A4

Start with the simplest possible case. Write down what Plexin-A4 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 Plexin-A4 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 Plexin-A4 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 Plexin-A4

In research: Plexin-A4 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 Plexin-A4 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: Plexin-A4 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genes on human chromosome 7, Protein stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Plexin-A4 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 Plexin-A4 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Plexin-A4 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 Plexin-A4 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Plexin-A4 in simple terms?

Plexin-A4 is a protein that in humans is encoded by the PLXNA4 gene. Plexin-A4 functions as a coreceptor for Semaphorin-3A and is involved in nervous system development.

Why does Plexin-A4 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 Plexin-A4?

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 Plexin-A4.