Clue 1: Orient yourself
How does opening one route affect the other route?
Use the labels and the picture's left-to-right, near-to-far, or before-and-after order. Name only what you can point to.
The question
Why did springy support tissue appear where hard bone should have formed when one message was removed?
Why it matters: The face forms through a timed sequence of growth, movement, and joining. Locating the missed step helps researchers ask a testable question instead of treating every cleft as the same process. Today you practice the professional reasoning behind that work: Wnt switches on Twist1, and Twist1 holds down Sox9 so cranial progenitors move away from cartilage and toward dermal and bone fates.
On your WebXam
Interpreting a loss-of-signal result as release of an intermediate brake on a default fate
For life
When something appears after you remove a signal, look for the brake that was holding it down.
Principle: Held down, not gone
Five principles we return to
Having it is not using it
Same instructions, different switches
Same look, different cause
Change one thing and watch
Boss or doorman?
Decides the result or only allows it
Held down, not gone
Remove the brake and it returns
Many roads, one ending
One result can begin many ways
Try the everyday version first
A railway switch selects one track and closes another
A railway switch guides a train toward one track while keeping it off another. The train is present either way, but the switch changes its destination.
Do not jump to the biology yet. Treat the picture as a small system. Track its parts, follow one change at a time, and keep more than one explanation open until the picture supplies a way to separate them.
Clue 2: Trace one change
What outcome would show that the switch decides the result?
Follow one object, stage, or path. Point to the first place where the situation changes instead of jumping to the ending.
Clue 3: Keep the cause open
Why must the starting cells be comparable?
List more than one explanation that still fits. Name the extra observation that would help you separate those possibilities.
Now inspect the illustration
Work from the visible evidence. A useful answer names the part of the picture that supports it and leaves unknown causes open.
- 1How does opening one route affect the other route?
- 2What outcome would show that the switch decides the result?
- 3Why must the starting cells be comparable?
Tier 1 check
Finish with the everyday model
Use the everyday picture to answer today's question in plain words: Why did springy support tissue appear where hard bone should have formed when one message was removed?
You can complete today's required check without opening the technical details below.
Ready for the real names? Optional tier 2
Technical rules and limits
Rule 1: Cell fate involves both activation and repression.
Rule 2: Removing a signal can reveal a default or competing fate.
Rule 3: Lineage labels show what the same progenitors become.
Where the analogy stops: Cell fate is controlled by interacting genes and signals, not one steel lever.
Carry the previous idea forward
TGF-beta3 makes the palatal medial edge competent to complete adhesion and seam removal.
Today's technical takeaway
Wnt switches on Twist1, and Twist1 holds down Sox9 so cranial progenitors move away from cartilage and toward dermal and bone fates.
Now map the same rules onto biology
Map the Atit Lab beta-catenin experiment
Train
A lineage-labeled cranial progenitor
Open dermis-bone track
Wnt-beta-catenin signaling
Wrong destination after switch loss
Cartilage at the expense of dermal and bone fates
Educational illustration, not a clinical photograph. Use the labels and evidence cards to make the biological claim.
Mateo's case file: evidence supplied in this lesson
DEV12-E1
Control cranial progenitors process Wnt-beta-catenin signaling during fate selection.
Why it matters: The pathway is active during the decision window.
DEV12-E2
Conditional beta-catenin loss removes cranial dermis and bone in the tested region.
Why it matters: The pathway is required for those fates in that model.
DEV12-E3
Lineage-labeled mutant cells form cartilage in their place.
Why it matters: The same progenitor population changed fate rather than simply disappearing.
Make the clinical decision
You are the student lead for an Atit Lab figure discussion.
A classmate says the mutant has less dermis only because all labeled cells died.
AUse labeled cartilage descendants to support a fate switch.
BAgree that lineage labels cannot show descendants.
CClaim Wnt controls every cell fate in the embryo.
Choose the strongest response and cite the evidence that rules against simple cell loss.
Evidence required
DEV12-E1 + DEV12-E2 Claim ceiling
You may support an instructive Wnt role in the tested cranial lineage. You may not generalize to every tissue or developmental stage.Go deeper Optional tier 3
Everything required for today is above. Open these only if you want the explainer, source trail, or download files.
The everyday model and Tier 1 check are the complete required path for this lesson.
Use these checks to keep your place. They are not turned in through the portal.
Check off as you finish
- Worked through the everyday picture and answered its three questions.
- Completed the Tier 1 check in plain words.
Turn in: Developmental lesson 12: The Wnt to Twist1 to Sox9 Brake, How a Face Cell Avoids Cartilage
Go to Schoology to turn this in.
Submit one PDF. Put your first and last name in the document header. Name the file: FirstName LastName - Assignment Title - YYYY-MM-DD.pdf.
Open Schoology PDF upload helpIf you cannot get in, see Mr. Mendoza. Do not skip the work.
Optional legacy technical materials Open only if you want the original notes, vocabulary, artifact, and CER work
Before this page, you should know
- is a that acts as the switch for the , not a growth or movement gene.
- It turns on only in the , the thin strip of cells that will touch the opposite shelf, by about mouse day E13, right before contact.
Today's new idea is only
Wnt switches on Twist1, and Twist1 holds down Sox9, the gene, so the cell can move toward bone or skin instead.
Goal: Explain that Wnt switches on Twist1 and Twist1 holds down Sox9, then predict the when Wnt or Twist1 is lost.
Know by the end
- A single cranial cell can become bone (), skin (dermal fibroblast), or (chondrocyte), choosing at about mouse day E11.5.
- is the : the fate the cell takes when nothing tells it otherwise.
- Wnt/ switches on the brake Twist1.
- Twist1 holds down Sox9, the gene. Remove Wnt or Twist1 and cartilage can appear where bone or skin should have formed.
1
The surprising logic of the switch
Model start: Every young cell faces a cell fate decision. In cranial , Wnt switches on Twist1, and Twist1 holds down Sox9.
- The of these cells, the one they take when no one tells them otherwise, is ____ ().
- Wnt/ switches on the brake ____ (Twist1).
- Twist1 holds down the gene ____ (Sox9). Remove Wnt and the Twist1 brake releases, so the cells can default to cartilage where bone or skin should have been.
2
An honest open question
- Scientists first guessed Twist1 might use a chromatin system called ____ (PRC2). The Atit Lab tested it and found PRC2 was dispensable.
- Twist1 is a major part of the brake, but not the whole story. A parallel ERK arm and partial fate reversion show that the deeper mechanism remains ____ (open).
Everything you need for today is on this page. These links are optional.
What to read
Read the short plain-language explanation written for this lesson. Plain-language explainer for this lesson
Why this source matters
This explanation gives you the background for today's idea without making you decode a research paper: Wnt switches on Twist1, and Twist1 holds down Sox9, the gene, so the cell can move toward bone or skin instead.
Words to unlock first
Reading moves
- Skim the title and abstract first to get the gist.
- Circle the one sentence that states the main claim.
- Box the evidence the authors give for that claim.
- Mark one sentence that confuses you, and move on.
Stop point
Stop after the final 'Use it now' section. The research citations are available separately for advanced readers.
Your output
Write one claim-evidence sentence: state the main idea, then name the example or evidence that supports it.
Where this fits
Tested on (Ohio WebXam)
Genetics of Disease · 072130
PLTW lesson
MI · Developmental domain · PLTW PBS 072110
WebXam domain
Molecular and Genetic Technology
Evidence to produce
Draw a decision tree for one cranial cell with two branches. Label the Wnt to Twist1 to Sox9 chain when Wnt is ON, then show what happens to Twist1, Sox9, and cell fate when Wnt is OFF.
Lab / skill
Principles of Biomedical Science (PBS)
Everything required for today's decision is already in the case file and plain-language explainer. The links below are original papers and database records for teachers and advanced readers, not assigned student reading.
- Goodnough et al. 2012 (Atit Lab), Twist1 Mediates Repression of Chondrogenesis by Beta-Catenin (Development)
- Goodnough et al. 2014 (Atit Lab), Distinct Requirements for Cranial Ectoderm and Mesenchyme-Derived Wnts (PLoS Genet)
- Tran et al. 2010 (Atit Lab), Role of canonical Wnt signaling/beta-catenin via Dermo1 (journal link; use class excerpt if blocked)
- Ibarra, Machen, and Atit 2021, A Wnt-Dependent ERK Pathway Represses Sox9 in Cranial Mesenchyme (Journal of Developmental Biology)
- Ferguson et al. 2018 (Atit Lab), PRC2 Is Dispensable for beta-Catenin-Mediated Repression of Chondrogenesis (journal link; use class excerpt if blocked)
- Claim: Wnt switches on Twist1, and Twist1 holds down Sox9 so does not replace bone or skin.
- Evidence: When Wnt was removed, Twist1 decreased and the cells became ____ instead of bone or skin.
- Reasoning: If removing Wnt lowers Twist1 and releases Sox9, then Twist1 is a major part of the active ____ on .
How this is graded (rubric)
For: Draw a decision tree for one cranial cell with two branches. Label the Wnt to Twist1 to Sox9 chain when Wnt is ON, then show what happens to Twist1, Sox9, and cell fate when Wnt is OFF.
| Criterion | Proficient | Developing | Beginning |
|---|---|---|---|
| Complete | Every required part of the artifact is present and filled in. | Most parts are present, but one is missing or left blank. | Several parts are missing. |
| Accurate | The science and data are correct and match the evidence. | Mostly correct, with a small factual slip. | Key science or data is wrong. |
| Scientific reasoning (CER) | States a claim, backs it with specific evidence, and explains the reasoning. | Has a claim and evidence, but the reasoning is thin or missing. | Gives an answer with no evidence or reasoning. |
| Professional communication | Clear, organized, and labeled the way a clinician or scientist would write it. | Readable but disorganized or missing labels. | Hard to follow. |
| Submitted | Turned in through the route named under Submit here and confirmed. | Turned in, but in the wrong place or unconfirmed. | Not turned in. |
How the model answer scores against this rubric
- CompleteProficient: Nothing is left blank: the model fills every part of "Draw a decision tree for one cranial cell with two branches. Label the Wnt to Twist1 to Sox9 chain when Wnt is ON, then show what happens to Twist1, Sox9, and cell fate when Wnt is OFF.".
- AccurateProficient: Every number and claim matches the case evidence.
- Scientific reasoning (CER)Proficient: It names a claim, cites the specific evidence, and explains the reasoning, not just the answer.
- Professional communicationProficient: It is organized and labeled like a real chart note.
- SubmittedProficient: It would be attached to your class form or handed in, and confirmed.
What's next: We now see how cells choose their fate. But happens at surfaces, and surfaces are dangerous: a sticky outer layer could glue the to the tongue by accident. So why do not the wrong surfaces stick together?