What Happens to the Wall Between the Shelves: Seam Removal, EMT versus Apoptosis
What happens to the wall of seam cells so the becomes one continuous , and how sure are scientists about the answer?
💡 The is only finished when the seam is removed, and exactly HOW the seam cells leave is a real scientific question that better imaging keeps refining.
Prerequisite check
- The -facing edge of each elevated shelf is covered by the , and the very outside is capped by the .
- The is a non-stick protective layer whose normal job is to keep embryonic surfaces from sticking.
What you will learn
Goal: Explain that the seam must be removed for the to become one continuous , and compare the candidate mechanisms (EMT, , cell , and live-) as a genuine, still-evolving scientific question.
- For the to be one , the on the left and right must become continuous, which requires removing the seam between them.
- Scientists agree the seam disappears, but they have proposed different mechanisms for how its cells leave: EMT, , , and live-.
- found little evidence that seam cells convert to (EMT) and pointed toward plus ; recent favors -driven extrusion plus apoptosis.
- This is normal science: the conclusion (the seam goes away) is settled while the cellular mechanism is still being argued.
Model: The seam must disappear, and four candidate explanations
Picture the joined roof in cross section: running down the middle is the , a thin column of cells where the two edges met, with on both sides still separated by that wall. For the to work as one , the left mesenchyme must become continuous with the right, which can only happen if the seam is removed. Lab records show the MES thins, breaks into islands, and is gone, leaving uninterrupted mesenchyme across the . So the seam does disappear; the question is HOW its cells leave.
Researchers proposed several mechanisms, and the favored answer changed as imaging improved. Idea A, EMT: the seam cells convert into and blend in (cells switch teams, not lost). Idea B, : the cells get a self-destruct signal and die in an orderly way. Idea C, : the cells slide away from the without dying or changing identity. Idea D, live-: the seam cells pull on each other, gather into rosettes, and get physically squeezed out of the sheet while still alive, with apoptosis as a partner. Early work leaned toward EMT; then found little evidence for conversion and pointed to apoptosis plus migration; the most recent favors -driven extrusion working with apoptosis.
Explore (work the model before reading on)
- What has to become continuous across the for the to be one , and what is in the way?
- List the four candidate explanations for what happens to the seam cells in your own short words.
- Which idea was favored early, and which is favored by the most recent imaging?
- If you could tag seam cells and follow them, what would you EXPECT to see for EMT versus for , and how could that tag tell the two apart?
- A classmate says the seam disappears, so the mechanism does not matter. Give one reason a developmental biologist WOULD care which mechanism is correct.
Guided notes
The seam must go
- Scientists agree the seam ____, but they propose different mechanisms for how its cells leave.
- The classic candidates are EMT (cells convert to ), (cells die in an orderly way), and ____ (cells slide away).
Better tools, better answers
- Using ____ labeling, researchers found little evidence for large-scale EMT and more support for plus .
- The newest shows seam cells contract, form rosettes, and undergo live-cell ____ (extrusion).
Two layers of certainty
- The conclusion (the seam goes away) is ____, while the mechanism is still being argued.
- For Mateo, seam-removal failure stays a possible cause, not something visible on a ____ exam.
Reading the Research
- 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.
Vetted readings for this lesson
- Lan & Jiang 2015, Cellular and Molecular Mechanisms of Palatogenesis (Curr Top Dev Biol)
- Bush & Jiang 2011, Palatogenesis: morphogenetic and molecular mechanisms of secondary palate development (Development)
- Won et al. 2023, Gene Regulatory Networks and Signaling Pathways in Palatogenesis and Cleft Palate (Cells)
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.
- 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: Write the "open questions" box for Mateo's case file: (1) state what is settled (the seam must be removed for one continuous palate), (2) name the competing mechanisms, (3) say which is currently favored and why (better imaging), and (4) note honestly that the question is not fully closed. Add one line that seam-removal failure stays a possible upstream cause, not something visible on newborn exam.
- Wrote my Claim, Evidence, and Reasoning exit ticket.
Exit ticket (Claim, Evidence, Reasoning)
- Claim: For the to become one , the ____ must be removed.
- Evidence: Scientists proposed ____, , , and extrusion; found little ____ and recent imaging favors -driven extrusion plus apoptosis.
- Reasoning: This is a good example of science because the conclusion is settled while the ____ is still being refined by better tools, and for Mateo it stays an possibility we cannot confirm from the outside.
| 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. |
- CompleteProficient: Nothing is left blank: the model fills every part of "Write the "open questions" box for Mateo's case file: (1) state what is settled (the seam must be removed for one continuous palate), (2) name the competing mechanisms, (3) say which is currently favored and why (better imaging), and (4) note honestly that the question is not fully closed. Add one line that seam-removal failure stays a possible upstream cause, not something visible on newborn exam.".
- 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.
Where this leads: careers
What's next: The seam is removed, by mechanisms scientists are still working out, so the becomes one continuous . But the seam cells clear at exactly the right time and place, and the shelves grew the right amount and stuck only where they should. Something must be telling the tissue when and where to grow, stick, and clear. What is that signal, and where does it come from? We chase that next time.