Summary
A morphogen pathway patterning the neural tube and limbs through Gli transcription factors.
In depth
Hedgehog binds Patched, relieving inhibition of Smoothened, so Gli factors activate targets. Shh patterns the neural tube floor plate, limbs and face. Defects cause holoprosencephaly; basal cell carcinoma involves pathway activation.
Hedgehog proteins are cholesterol-modified and form gradients. Patched is a receptor that represses Smoothened; binding releases this block. Primary cilia are required in vertebrates.
Remember: Shh mutations cause holoprosencephaly.
The Hedgehog pathway, first found in fly mutants with spiky larvae, is activated when a Hedgehog protein (Sonic, Indian or Desert in mammals) binds to the receptor Patched, which relieves inhibition of Smoothened. This leads to activation of Gli transcription factors.
Sonic hedgehog from the notochord and floor plate patterns the neural tube along the dorsal-ventral axis, and from the ZPA patterns digits. It also controls face and brain development: loss causes holoprosencephaly, in which the forebrain fails to split. Primary cilia are needed in vertebrates.
Example: basal cell carcinoma often involves mutations in Patched.
Key idea: Hedgehog acts as a classic morphogen.
Frequently asked questions
What is Hedgehog Signalling?
A morphogen pathway patterning the neural tube and limbs through Gli transcription factors.
Which area of biology covers Hedgehog Signalling, and how advanced is it?
Hedgehog Signalling is one of the 54 topics in Developmental Biology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include BMP and TGF-Beta Signalling, Notch Signalling, Morphogens.
Can you give an example of Hedgehog Signalling?
Cyclopamine, a plant alkaloid, blocks Smoothened and causes cyclopia in lambs.
What should I learn before Hedgehog Signalling?
Work through the Beginner topics in Developmental Biology first, such as Fertilisation, Zygote, Embryo, then return to Hedgehog Signalling. Advanced topics assume the Intermediate vocabulary.
What topics are related to Hedgehog Signalling?
The closest topics to Hedgehog Signalling are BMP and TGF-Beta Signalling, Notch Signalling, Morphogens, Wnt Signalling. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Hedgehog Signalling?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Hedgehog Signalling. To practise the whole of Developmental Biology, use the Developmental Biology quiz.
How is Hedgehog Signalling different from BMP and TGF-Beta Signalling?
Hedgehog Signalling: A morphogen pathway patterning the neural tube and limbs through Gli transcription factors. BMP and TGF-Beta Signalling: Signals that pattern dorsal-ventral axes and regulate differentiation via SMAD proteins. Read both side by side and note what each one explains.
How should I study Hedgehog Signalling step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with BMP and TGF-Beta Signalling and explain the difference aloud. Finally, take the Developmental Biology quiz and come back to this page for any question you miss.