biology

Insulin-like growth factor 2

Insulin-like growth factor 2 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 Insulin-like growth factor 2 rather than just read about it. In short: Insulin-like growth factor 2 (IGF-2) is one of three protein hormones that share structural similarity with insulin. The MeSH definition reads: "A well-characterized neutral peptide believed to be secreted by the liver and to circulate in the blood.

Key takeaways

Insulin-like growth factor 2 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Insulin-like growth factor 2 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Insulin-like growth factor 2 from memory before moving on to harder problems.

Reference excerpt

Insulin-like growth factor 2 (IGF-2) is one of three protein hormones that share structural similarity with insulin. The MeSH definition reads: "A well-characterized neutral peptide believed to be secreted by the liver and to circulate in the blood. It has growth-regulating, insulin-like and mitogenic activities. The growth factor has a major, but not absolute, dependence on somatotropin. It is believed to be a major fetal growth factor in contrast to insulin-like growth factor 1 (IGF-1), which is a major growth factor in adults."

Gene structure In humans, the IGF2 gene is located on chromosome 11p15.5, a region which contains numerous imprinted genes. In mice this homologous region is found at distal chromosome 7. In both organisms, IGF2 is imprinted, with expression resulting favourably from the paternally inherited allele. However, in some human brain regions a loss of imprinting occurs resulting in both IGF2 and H19 being transcribed from both parental alleles. The protein CTCF is involved in repressing expression of the gene, by binding to the H19 imprinting control region (ICR) along with Differentially-methylated Region-1 (DMR1) and Matrix Attachment Region −3 (MAR3). These three DNA sequences bind to CTCF in a way that limits downstream enhancer access to the IGF2 region. The mechanism in which CTCF binds to these regions is currently unknown, but could include either a direct DNA-CTCF interaction or it could possibly be mediated by other proteins. In mammals (mice, humans, pigs), only the allele for insulin-like growth factor-2 (IGF2) inherited from one's father is active; that inherited from the mother is not—a phenomenon called imprinting. The mechanism: the mother's allele has an insulator between the IGF2 promoter and enhancer. So does the father's allele, but in his case, the insulator has been methylated. CTCF can no longer bind to the insulator, and so the enhancer is now free to turn on the father's IGF2 promoter. The canonical isoform of IGF-2 preproprotein (180 amino acids) includes a signal peptide (amino acids 1-24) and a propeptide (amino acids 92-180). Proteolytic processing removes the signal peptide and the propeptide to generate the mature hormone (amino acids 25-91).

Function The major role of IGF-2 is as a growth promoting hormone during gestation. IGF-2 exerts its effects by binding to the IGF-1 receptor and to the short isoform of the insulin receptor (IR-A or exon 11-). IGF-2 may also bind to the IGF-2 receptor (also called the cation-independent mannose 6-phosphate receptor), which acts as a signalling antagonist; that is, to prevent IGF-2 responses. In the process of folliculogenesis, IGF-2 is created by thecal cells to act in an autocrine manner on the theca cells themselves, and in a paracrine manner on granulosa cells in the ovary. IGF-2 promotes granulosa cell proliferation during the follicular phase of the menstrual cycle, acting alongside follicle stimulating hormone (FSH). After ovulation has occurred, IGF-2 promotes progesterone secretion during the luteal phase of the menstrual cycle, together with luteinizing hormone (LH). Thus, IGF-2 acts as a co-hormone together with both FSH and LH. A study at the Mount Sinai School of Medicine found that IGF-2 may be linked to memory and reproduction. A study at the European Neuroscience Institute-Goettingen (Germany) found that fear extinction-induced IGF-2/IGFBP7 signalling promotes the survival of 17- to 19-day-old newborn hippocampal neurons. This suggests that therapeutic strategies that enhance IGF-2 signalling and adult neurogenesis might be suitable to treat diseases linked to excessive fear memory such as PTSD.

Preptin Preptin, a 34-aa peptide hormone produced by the pancreas, kidneys, breast tissues, and salivary glands, is derived from proteolytic cleavage of IGF-2 proprotein. The sequence of preptin (amino acids 93-126 of canonical IGF-2 preproprotein) is flanked by an N-terminal arginine (Arg) cleavage site and a C-terminal putative dibasic (Arg-Arg) cleavage motif. Preptin is present in islet beta-cells, undergoes glucose-mediated co-secretion with insulin, and acts as a physiological amplifier of glucose-mediated insulin secretion. It has an anabolic impact on bone growth and exhibits osteogenic properties, increasing osteoblast mitogenic activity through phosphoactivation of MAPK1 and MAPK3. This activity resides within the first 16 amino acids of preptin. Genetic ablation of the preptin-coding region of Igf2 in female mice impairs pancreatic function.

Clinical relevance IGF-2 is sometimes produced in excess in islet cell tumors and non-islet hypoglycemic cell tumors, causing hypoglycemia. Doege-Potter syndrome is a paraneoplastic syndrome in which hypoglycemia is associated with the presence of one or more non-islet fibrous tumors in the pleural cavity. Loss of imprinting of IGF-2 is a common feature in tumors seen in Beckwith-Wiedemann syndrome. As IGF-2 promotes development of fetal pancreatic beta cells, it is believed to be related to some forms of diabetes mellitus. Preeclampsia induces a decrease in methylation level at IGF-2 demethylated region, and this might be among the mechanisms behind the association between intrauterine exposure to preeclampsia and high risk for metabolic diseases in the later life of the infants. In animals it has been shown that toxins such as PCB (polychlorinated biphenyls) affects IGF II expression.

Interactions Insulin-like growth factor 2 has been shown to interact with IGFBP3 and transferrin.

See also Insulin-like growth factor 2 receptor Insulin-like growth factor II IRES

References

Illustrations

Worked examples

Example 1 — a first encounter with Insulin-like growth factor 2

Start with the simplest possible case. Write down what Insulin-like growth factor 2 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 Insulin-like growth factor 2 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 Insulin-like growth factor 2 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 Insulin-like growth factor 2

In research: Insulin-like growth factor 2 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 Insulin-like growth factor 2 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: Insulin-like growth factor 2 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genes on human chromosome 7, Hormones of the somatotropic axis, Insulin-like growth factor receptor agonists, so understanding it makes those chapters shorter.
In everyday life: Look for Insulin-like growth factor 2 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 Insulin-like growth factor 2 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Insulin-like growth factor 2 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 Insulin-like growth factor 2 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Insulin-like growth factor 2 in simple terms?

Why does Insulin-like growth factor 2 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 Insulin-like growth factor 2?

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 Insulin-like growth factor 2.