Rough draft.This research track is under review with Dr. Atit's lab. Content and sequence may still change.
The Baby Mateo Case
Developmental domainPrinciples of Biomedical Science (PBS)Lesson 12 of 20Your seat: Developmental biologist (Atit Lab collaboration)
The Wnt/beta-catenin Master Switch, How a Face Cell Decides What NOT to Be
Discovery question
How does a single cranial cell decide whether to become bone, skin, or , and what is the off choice it has to actively avoid?
💡 Wnt/ does not mainly tell a cranial cell what to be; it represses the default program so the cell is free to become bone or skin.
The plan
Prerequisite check
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/ does not mainly tell a cranial cell what to be; it represses the default program so the cell is free to become bone or skin.
Learn first
What you will learn
Goal: Explain that Wnt/ signaling tells a cranial cell to become bone or skin by actively repressing the default program, and predict the when that signal 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/ works by , switching OFF the program (Sox9) so the cell can become bone or skin.
- Remove the Wnt signal and ectopic appears where bone or skin should have formed (Atit Lab mouse data).
Learn first
Model: Turn off the signal, watch the fate flip (Atit Lab mouse data)
The Atit Lab at Case Western Reserve University, the lab partnering with John Hay Biomedical, can switch OFF Wnt signaling in cranial cells by deleting the gene that lets cells release Wnt.
With the Wnt/ signal present (normal), bone and skin formed normally and almost no appeared. With the signal removed, bone and skin FAILED and ectopic cartilage appeared inside the future bone area. The cells did not just stop; they defaulted to cartilage in a place that should have been bone. The authors call cartilage a default state that Wnt signaling normally overrides (PMID:24586192; PMID:20980404).
Do the work
Explore (work the model before reading on)
- Name the three fates one cranial cell can take.
- What fate appeared when Wnt was removed, and where did it appear?
- When the Wnt signal disappears the cells did not just stop, they became something specific. What does that tell you about being the default?
- So what is the real job of the Wnt signal: to TELL a cell to become , or to STOP it from becoming cartilage so it can be bone or skin instead?
- Predict what you would see if a small patch of face had weak Wnt signaling during the time bone should form. What would show up where bone belongs?
The plan
Guided notes
1
The surprising logic of the switch
Model start: Every young cell faces a cell fate decision: which mature cell type it will become. In the cranial , Wnt/ is the master switch.
- The of these cells, the one they take when no one tells them otherwise, is ____ ().
- Wnt/ works by : it switches OFF the program (Sox9) so the cell can become ____ (bone) or ____ (skin/dermis).
- Remove the Wnt signal and the brake on releases, so the cells default to ____ (cartilage) where bone or skin should have been.
2
An honest open question
- Scientists first guessed Wnt blocks through a chromatin system called ____ (PRC2). The Atit Lab tested it and found it was dispensable.
- stayed off without PRC2, so the exact brake is still ____ (unknown). A clean experiment ruled out the favorite answer.
Explore
Reading the Research
What to read
Read the title and the abstract only, not the whole paper. Goodnough et al. 2014 (Atit Lab), Distinct Requirements for Cranial Ectoderm and Mesenchyme-Derived Wnts (PLoS Genet)
Why this source matters
This is the published evidence behind today's idea: Wnt/ does not mainly tell a cranial cell what to be; it represses the default program so the cell is free to become bone or skin.
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
You do not need the methods or statistics yet. If a sentence is about lab technique or math you have not learned, mark it and skip it.
Your output
Write one claim-evidence sentence: what this source claims, and the one piece of evidence that backs it up.
Where this fits
Tested on (Ohio WebXam)
Genetics of Disease · 072130
PLTW lesson
MI · Developmental domain · PLTW PBS 072110
WebXam domain
Bio-Molecular Technology
Evidence to produce
Draw a decision tree for one cranial cell with two branches. Label the branch taken when Wnt is ON (bone or skin) and the branch taken when Wnt is OFF (cartilage, the default). In one sentence, finish this idea: "The Wnt master switch matters because it tells a cell what ____."
Lab / skill
Principles of Biomedical Science (PBS)
Explore
Vetted readings for this lesson
- 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)
- Ferguson et al. 2018 (Atit Lab), PRC2 Is Dispensable for beta-Catenin-Mediated Repression of Chondrogenesis (journal link; use class excerpt if blocked)
The plan
Track your progress today
Check these off as you work through the lesson, then submit. This tells Mr. Mendoza how you're doing so he can help the class. It does not replace turning in your producible.
Use the code Mr. Mendoza gave you, not your name. Saved on this device.
Check off as you finish
- Read the Model and answered the Explore questions.
- Filled in the guided notes in my own words.
- Defined the new vocabulary with an example.
- Built the producible: Draw a decision tree for one cranial cell with two branches. Label the branch taken when Wnt is ON (bone or skin) and the branch taken when Wnt is OFF (cartilage, the default). In one sentence, finish this idea: "The Wnt master switch matters because it tells a cell what ____."
- Wrote my Claim, Evidence, and Reasoning exit ticket.
Pick your period and code first.
Check yourself
Exit ticket (Claim, Evidence, Reasoning)
- Claim: The Wnt master switch works mainly by telling a cell what NOT to become.
- Evidence: When Wnt was removed, the cells became ____ instead of bone or skin.
- Reasoning: If removing the signal releases the program, then the signal's normal job must be to ____ that program.
How this is graded (rubric)
For: Draw a decision tree for one cranial cell with two branches. Label the branch taken when Wnt is ON (bone or skin) and the branch taken when Wnt is OFF (cartilage, the default). In one sentence, finish this idea: "The Wnt master switch matters because it tells a cell what ____."
| 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 the right way (Schoology for routine work) 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 branch taken when Wnt is ON (bone or skin) and the branch taken when Wnt is OFF (cartilage, the default). In one sentence, finish this idea: "The Wnt master switch matters because it tells a cell what ____."".
- 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 turned in on Schoology and confirmed.
Explore
Where this leads: careers
Developmental biologist Stem cell researcher
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?
TGF-beta3, the Fusion Switch in the Medial Edge EpitheliumPeriderm and IRF6, the Non-Stick Coating on the Embryo