biology

IsomiR

IsomiR 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 IsomiR rather than just read about it. In short: isomiRs (from iso- + miR) are miRNA sequences that have variations with respect to the reference sequence. The term was coined by Morin et al in 2008.

Key takeaways

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

Reference excerpt

isomiRs (from iso- + miR) are miRNA sequences that have variations with respect to the reference sequence. The term was coined by Morin et al in 2008. It has been found that isomiR expression profiles can also exhibit race, population, and sex dependencies. There are four main variation types:

5' trimming—the 5' dicing site is upstream or downstream from the reference miRNA sequence 3' trimming—the 3' dicing site is upstream or downstream from the reference miRNA sequence 3' nucleotide addition—nucleotides added to the 3' end of the reference miRNA nucleotide substitution—nucleotides changes from the miRNA precursor. It is thought that may be similar process than post-transcriptional modifications.

Discovery miRBase is considered to be the gold-standard miRNA database—it stores miRNA sequences detected by thousand of experiments. In this database each miRNA is associated with a miRNA precursor and with one or two mature miRNA (-5p and -3p). In the past it had always been said that the same miRNA precursor generates the same miRNA sequences. However, the advent of deep sequencing has now allowed researchers to detect a huge variability in miRNA biogenesis, meaning that from the same miRNA precursor many different sequences can be generated potentially have different targets, or even lead to opposite changes in mRNA expression.

Biogenesis The advent of sequencing has permitted scientists to elucidate a huge landscape of new miRNAs, to increase our knowledge of the biogenesis involved and to discover putative post-transcriptional editing processes in miRNAs ignored until now. These processes mostly generate variations of the current miRNAs that are annotated in miRBase in the 3' and 5' terminus and in minor frequencies, nucleotide substitution along the miRNA length. The variations are mainly generated by a shift of Drosha and Dicer in the cleavage site, but also by nucleotide additions at the 3'-end, resulting in new sequences different from the annotated miRNA. These were named "isomiRs" by Morin et al., 2008. IsomiRs have been well established along different species in metazoa and deeply described for the first time in human stem cells and human brain samples. Moreover, it has been proven that isomiRs are not caused by RNA degradation during sample preparation for next generation sequencing. Some studies have tried to explain the miRNA diversity by structural bases of precursors but without clear results. The functionality of adenylation or uridynilation at the 3'end (3'addition isomiRs) has been related to alterations in the miRNA-3'-UTR stability. Furthermore, differential expression of isomiRs has been detected during development in D. melanogaster and Hippoglossus hippoglossus L., suggesting a biological function.

Trimming variants: these are possible due to slight variations by Drosha and/or Dicer Nucleotide addition: Wyman et al. have described the process of nucleotide transferases adding individual nucleotides to miRNA sequences Nucleotide substitution: there is a huge range of possible changes in such an event, some of them can be explained by current adenosine_deaminase like A to G or C to U, in a similar way to what happens in post-transcriptional RNA editing events involving mRNA.

References

External links miRBase

Illustrations

Worked examples

Example 1 — a first encounter with IsomiR

Start with the simplest possible case. Write down what IsomiR 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 IsomiR 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 IsomiR 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 IsomiR

In research: IsomiR 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 IsomiR 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: IsomiR is common in secondary-school and first-year university syllabi. It links to neighbouring topics Gene expression, MicroRNA, RNA, so understanding it makes those chapters shorter.
In everyday life: Look for IsomiR 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 IsomiR in 20 minutes

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

Frequently asked questions

What is IsomiR in simple terms?

isomiRs (from iso- + miR) are miRNA sequences that have variations with respect to the reference sequence. The term was coined by Morin et al in 2008.

Why does IsomiR 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 IsomiR?

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 IsomiR.