MiR-125

Key takeaways

MiR-125 belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect MiR-125 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of MiR-125 from memory before moving on to harder problems.

Reference excerpt

MicroRNA-125 (miR-125) is a highly conserved microRNA family consisting of miR-125a and miR-125b.MiR-125 can be found throughout diverse species from nematode to humans. MiR-125 family members are involved in cell differentiation, proliferation and apoptosis as a result of targeting messenger RNAs related to these cellular processes. By affecting these cellular processes, miR-125 can cause promotion or suppression of pathological processes including carcinogenesis, muscle abnormalities, neurological disorders and pathologies of the immune system. Moreover, miR-125 also plays an important role in normal immune functions and was described to affect development and function of immune cells as well as playing role in immunological host defense in response to bacterial and viral infections.

Genome location and biogenesis Each member of miR-125 family has two different variants of mature miRNAs - 5p and 3p. Both variants originate from the same pre-miRNA. MiR-125-5p variant generally shows higher expression compared to miR-125-3p. In humans, miR-125 family is composed of three homologs: hsa-miR-125a, hsa-miR-125b-1 and hsa-miR-125b-2. MiR-125a has been found to be located on chromosome 19, while paralogs of miR-125b are transcribed from two loci on chromosome 11 and chromosome 21.

Brain As a brain-enriched microRNA, miR-125b participates in neuronal differentiation but also in many diseases associated with degenerating brain tissues. MiR-125b promotes neuronal differentiation, thus levels of this microRNA get higher during neurogenesis. MiR-125b can contribute to the process of neuronal differentiation by targeting cyclin-dependent kinase inhibitor 2A (CDKN2A), a negative regulator of the cell cycle. On the other hand, downregulation of CDKN2A correlates with chronic neurological disorders associated with astrogliosis, such as advanced Alzheimer disease.

Muscle MiR-125 family is related to cardiomyocytes and the development of heart in embryonic period of mammals. Decreased levels of miR-125 can cause abnormal development of the cardiovascular system in these early stages. MiR-125 plays role in a variety of cardiovascular and cerebrovascular diseases, in their occurrence and development. The same family members of miR-125 can play different roles in different pathological processes. For instance, high levels of miR-125b can protect cardiomyocytes from apoptosis and inflammation. While at the same time, overexpression of miR-125 can support cardiac fibrosis by enhancing proliferation of fibroblasts and reducing their apoptosis. Significantly increased levels of miR-125b have also been found in patients with heart failure. MiR-125b can also negatively regulate skeletal myoblast differentiation and muscle regeneration by targeting insulin-like growth factor II (IGF-II). Decreased levels of this microRNA were noted during these processes. However, overexpression of miR-125b, especially the miR-125b-5p form, can protect skeletal muscle from atrophy.

Role in immune system Targets of miR-125 are involved in regulation of hematopoiesis, inflammation and many immune cells function. Different expression levels of miR-125 are found among different types of immune cells and stages of hematopoiesis. Principally, expression of both miR-15a and miR-125b decreases during the process of cell differentiation. Higher expression levels are found in hematopoietic stem cells (HSCs) and are associated with elevation of self-renewal and survival in these cells. Increased expression of miR-125a improves long-term multi-lineage repopulation and self-renewal of HSCs by blocking apoptosis pathways. MiR-125b can even block terminal differentiation of hematopoietic progenitors and also regulate HSC homeostasis by shifting the balance of TGFβ and Wnt signaling pathways. Additionally, miR-125b is associated with an impairment of B cell development and plays role in mainly negative regulation of T cell development. MiR-125b can affect inflammation by targeting TNF-α, enhancing the stability of NF-κB inhibitor NKIRAS2 and also by promotion of differentiation and activation of macrophages. Increased levels of miR-125b may enhance expression of type I interferons and participate in antiviral defense. For instance, this miRNA contributes to HIV-1 latency by destabilization of HIV-1 transcript by binding to its 3' end. And miR-125a was described to interfere with transcript of hepatitis B virus. MiR-125 can also participate in regulation of immune response against bacterial infection. Upregulated levels of miR-125 can contribute to turning off the TLR signaling in the absence of microbial infection. While downregulation of this miRNA can support inflammatory response. MiR-125 was also described to suppress the development of rheumatoid arthritis by inhibition of PI3K/Akt/mTOR signalling pathway via PARP2 targeting.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with MiR-125

Start with the simplest possible case. Write down what MiR-125 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, 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 MiR-125 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 MiR-125 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 MiR-125

In research: MiR-125 appears in chemistry 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 MiR-125 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: MiR-125 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cells, MicroRNA, Nematode nucleic acids, so understanding it makes those chapters shorter.
In everyday life: Look for MiR-125 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.

How to study MiR-125 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what MiR-125 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 MiR-125 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is MiR-125 in simple terms?

MicroRNA-125 (miR-125) is a highly conserved microRNA family consisting of miR-125a and miR-125b.MiR-125 can be found throughout diverse species from nematode to humans. MiR-125 family members are involved in cell differentiation, proliferation and apoptosis as a result of targeting messenger RNAs…

Why does MiR-125 matter?

Because it connects several chemistry 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 MiR-125?

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 MiR-125.