biology

Thrombopoietin

Thrombopoietin 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 Thrombopoietin rather than just read about it. In short: Thrombopoietin (THPO) also known as megakaryocyte growth and development factor (MGDF) is a protein that in humans is encoded by the THPO gene. Thrombopoietin is a glycoprotein hormone produced by the liver and kidney which regulates the production of platelets.

Key takeaways

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

Reference excerpt

Thrombopoietin (THPO) also known as megakaryocyte growth and development factor (MGDF) is a protein that in humans is encoded by the THPO gene. Thrombopoietin is a glycoprotein hormone produced by the liver and kidney which regulates the production of platelets. It stimulates the production and differentiation of megakaryocytes, the bone marrow cells that bud off large numbers of platelets. Megakaryocytopoiesis is the cellular development process that leads to platelet production. The protein encoded by this gene is a humoral growth factor necessary for megakaryocyte proliferation and maturation, as well as for thrombopoiesis. This protein is the ligand for MLP/C_MPL, the product of myeloproliferative leukemia virus oncogene.

Genetics The thrombopoietin gene is located on the long arm of chromosome 3 (q26.3-27). Abnormalities in this gene occur in some hereditary forms of thrombocytosis (high platelet count) and in some cases of leukemia. The first 155 amino acids of the protein share homology with erythropoietin.

Function and regulation Thrombopoietin is produced in the liver by both parenchymal cells and sinusoidal endothelial cells, as well as in the kidney by proximal convoluted tubule cells. Small amounts are also made by striated muscle and bone marrow stromal cells. In the liver, its production is augmented by interleukin 6 (IL-6). However, the liver and the kidney are the primary sites of thrombopoietin production. Thrombopoietin regulates the differentiation of megakaryocytes and platelets, but studies on the removal of the thrombopoietin receptor show that its effects on hematopoiesis are more versatile. Its negative feedback is different from that of most hormones in endocrinology: The effector regulates the hormone directly. Thrombopoietin is bound to the surface of platelets and megakaryocytes by the mpl receptor (CD 110). Inside the platelets it gets destroyed, while inside the megakaryocytes it gives the signal of their maturation and consecutively more platelet production. The bounding of the hormone at these cells thereby reduces further megakaryocyte exposure to the hormone. Therefore, the rising and dropping platelet and megakaryocyte concentrations regulate the thrombopoietin levels. Low platelets and megakaryocytes lead a higher degree of thrombopoietin exposure to the undifferentiated bone marrow cells, leading to differentiation into megakaryocytes and further maturation of these cells. On the other hand, high platelet and megakaryocyte concentrations lead to more thrombopoetin destruction and thus less availability of thrombopoietin to bone marrow. TPO, like EPO, plays a role in brain development. It promotes apoptosis of newly generated neurons, an effect counteracted by EPO and neurotrophins.

Therapeutic use Despite numerous trials, thrombopoietin has not been found to be useful therapeutically. Theoretical uses include the procurement of platelets for donation, and recovery of platelet counts after myelosuppressive chemotherapy. Trials of a modified recombinant form, megakaryocyte growth and differentiation factor (MGDF), were stopped when healthy volunteers developed autoantibodies to endogenous thrombopoietin and then developed thrombocytopenia. Romiplostim and Eltrombopag, compounds that are structurally different to thrombopoietin but stimulate the same pathway by binding to and activating the thrombopoietin receptor, are used instead. A quadrivalent peptide analogue is being investigated, as well as several small-molecule agents, and several non-peptide ligands of c-Mpl, which act as thrombopoietin analogues.

Discovery Thrombopoietin was cloned by five independent teams in 1994. Before its identification, its function has been hypothesized for as much as 30 years as being linked to the cell surface receptor c-Mpl, and in older publications thrombopoietin is described as c-Mpl ligand (the agent that binds to the c-Mpl molecule). Thrombopoietin is one of the Class I hematopoietic cytokines.

Illustrations

Worked examples

Example 1 — a first encounter with Thrombopoietin

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

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

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

Frequently asked questions

What is Thrombopoietin in simple terms?

Why does Thrombopoietin 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 Thrombopoietin?

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 Thrombopoietin.