PAX8

Key takeaways

PAX8 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect PAX8 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of PAX8 from memory before moving on to harder problems.

Reference excerpt

Paired box gene 8, also known as PAX8, is a protein which in humans is encoded by the PAX8 gene.

Function This gene is a member of the paired box (PAX) family of transcription factors. Members of this gene family typically encode proteins which contain a paired box domain, an octapeptide, and a paired-type homeodomain. The PAX gene family has an important role in the formation of tissues and organs during embryonic development and maintaining the normal function of some cells after birth. The PAX genes give instructions for making proteins that attach themselves to certain areas of DNA. This nuclear protein is involved in thyroid follicular cell development and expression of thyroid-specific genes. PAX8 releases the hormones important for regulating growth, brain development, and metabolism. Also functions in very early stages of kidney organogenesis, the Müllerian system, and the thymus. Additionally, PAX8 is expressed in the renal excretory system, epithelial cells of the endocervix, endometrium, ovary, fallopian tube, seminal vesicle, epididymis, pancreatic islet cells and lymphoid cells. PAX8 and other transcription factors play a role in binding to DNA and regulating the genes that drive thyroid hormone synthesis (Tg, TPO, Slc5a5 and Tshr). PAX8 (and PAX2) is one of the important regulators of urogenital system morphogenesis. They play a role in the specification of the first renal cells of the embryo and remain essential players throughout development. PAX8 has been shown to interact with NK2 homeobox 1.

Clinical significance The PAX8 gene is also associated congenital hypothyroidism due to thyroid dysgenesis because of its role in growth and development of the thyroid gland. A mutation in the PAX8 gene could prevent or disrupt normal development. These mutations can affect different functions of the protein including DNA binding, gene activation, protein stability, and cooperation with the co-activator p300. PAX gene deficiencies can result in development defects called Congenital Anomalies of the Kidney and Urinary Tract (CAKUT).

Cancer PAX8 mutations are associated with various forms of cancer.

Mechanisms PAX8 is considered a "master regulator transcription factor". As a master regulator, it is possible that it regulates expression of genes other than thyroid-specific. Several known tumor suppressor genes like TP53 and WT1 have been identified as transcriptional targets in human astrocytoma cells. Over 90% of thyroid tumors arise from follicular thyroid cells. A fusion protein, PAX8-PPAR-γ, is implicated in some follicular thyroid carcinomas and follicular-variant papillary thyroid carcinoma. The mechanism for this transformation is not well understood, but there are several proposed possibilities.

Inhibition of normal PPARy function by chimeric PAX8/PPARy protein through a dominant negative effect Activation of normal PPARy targets due to the over expression of the chimeric protein that contain all functional domains of wild-type PPAR y Deregulation of PAX8 function Activation of a set of genes unrelated to both wild-type PPARy and wild-type PAX8 pathways The PAX 8 gene has some association with follicular thyroid tumors. It has been observed that PAX8/PPAR y-positive tumors rarely express RAS mutations in combination. This suggests that follicular carcinomas develop in two distinct pathways either with PAX8/PPAR y or RAS. Alternate transcriptional splice variants, encoding different isoforms, have been characterized. The mechanism of switching on the genes is unknown. Some studies have suggested that the renal PAX genes act as pro-survival factors and allow tumor cells to resist apoptosis. Down regulation of the PAX gene expression inhibits cell growth and induces apoptosis. This could be a possible avenue for therapeutic targets in renal cancer. Some whole-genome sequencing studies have shown that PAX8 also targets BRCA1 (carcinogenesis), MAPK pathways (thyroid malignancies), and Ccnb1 and Ccnb2 (cell-cycle processes). PAX8 is shown to be involved in tumor cell proliferation and differentiation, signal transduction, apoptosis, cell polarity and transport, cell motility and adhesion.

Associated cancer types Mutations in this gene have been associated with thyroid dysgenesis, thyroid follicular carcinomas and atypical follicular thyroid adenomas. PAX8/PPARy rearrangement account for 30-40% of conventional type follicular carcinomas., and less than 5% of oncocytic carcinomas (aka Hurthle-Cell Neoplasms). Expression of PAX8 is increased in neoplastic renal tissues, Wilms tumors, ovarian cancer and Müllerian carcinomas. For this reason, the immunodetection of PAX8 is widely used for diagnosing primary and metastatic renal tumors. Re-activation of PAX8 (or Pax2) expression has been reported in pediatric Wilms Tumors, almost all subtypes of renal cell carcinoma, nephrogenic adenomas, ovarian cancer cells, bladder, prostate, and endometrial carcinomas. Expression of PAX8 is also induced during the development of cervical cancer. Tumors expressing the PAX8/PPARy are usually present in at a young age, small in size, present in a solid/nested growth pattern and frequently involve vascular invasion.

Illustrations

Worked examples

Example 1 — a first encounter with PAX8

Start with the simplest possible case. Write down what PAX8 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 PAX8 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 PAX8 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 PAX8

In research: PAX8 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 PAX8 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: PAX8 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genes on human chromosome 2, Transcription factors, so understanding it makes those chapters shorter.
In everyday life: Look for PAX8 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 PAX8 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what PAX8 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 PAX8 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is PAX8 in simple terms?

Paired box gene 8, also known as PAX8, is a protein which in humans is encoded by the PAX8 gene. Function This gene is a member of the paired box (PAX) family of transcription factors.

Why does PAX8 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 PAX8?

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 PAX8.