Morphogens help developing tissues form organized patterns by giving cells information about their position. This lesson introduces the morphogen concept, explains the classical concentration-gradient model, and traces key milestones in its history.
A morphogen is a signaling molecule that contributes to morphogenesis and pattern formation. In a rigorous definition, it acts directly on cells to produce responses that depend on its concentration, rather than causing a sequence of indirect inductions.
All flashcards
What is a morphogen?
A signaling molecule that helps organize developmental patterns by producing distinct cellular responses, often according to the signal concentration received.
What is a morphogen concentration gradient?
A spatial variation in signal concentration across a tissue. In the classical example, concentration is highest near a localized source and declines farther away.
How do concentration thresholds help create different cell identities?
Target genes respond at different signal levels. Cells exposed to different concentrations activate different combinations of genes, which can lead to distinct cell identities.
What does the French flag model illustrate?
It illustrates how a morphogen gradient can divide a tissue into domains with different gene-expression patterns, analogous to the differently colored bands of a flag.
Which two Drosophila examples are associated with morphogen research?
Bicoid is a gradient-forming transcription factor in the syncytial embryo, while Decapentaplegic (Dpp) is a secreted signaling protein shown to act as a morphogen during later development.
Quiz questions
Why can Bicoid diffuse among nuclei during early Drosophila development?Answer: The nuclei share cytoplasm before membranes form individual cells.
How do many secreted protein morphogens influence target-gene expression?Answer: They bind cell-surface receptors that relay signals to the nucleus.
What happens to Smoothened when SHH is absent?Answer: Patched inhibits Smoothened signaling.
How does ligand binding activate the TGF-β type I receptor?Answer: The type II receptor phosphorylates the type I receptor.
How can enhancer DNA make a target gene respond to lower transcription-factor activity?Answer: Many high-affinity binding sites can increase its responsiveness.
Based on the Wikipedia article Morphogen, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.