Two Shelves Become One Roof: Adhesion, the Medial Edge Epithelium, and the Seam
How do the touching edges of two separate shelves become a single, joined roof?
💡 Two shelves can only join if a non-stick layer () is removed on schedule so the two medial edge epithelia can adhere into one seam.
Prerequisite check
- Elevation is the step where each vertical rotates to above the tongue at about human week 8.
- Elevation depends on internal remodeling of the shelf, including the water-holding matrix molecule , plus external room as the tongue descends and the head grows wider.
What you will learn
Goal: Describe how the two elevated shelves adhere at their medial edge and form a single seam, and explain why a non-stick surface layer must be removed first.
- 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.
- For , the over the MEE must be cleared at the right moment, then the two bare MEE layers adhere and intercalate into a single .
- The gene program (IRF6 and partners) controls whether the clears on cue; if it is faulty, fails.
Model: A close-up of the shelf edge, and the sticking problem
Zoom in on the medial (-facing) edge of one elevated shelf. From inside out you see in the core (the growing inner ), a surface covering the edge whose midline-facing part is the , and capping the very outside a thin layer of flat protective cells called the . Think of the periderm as a non-stick wrapper that keeps embryonic surfaces from sticking to whatever they brush against.
Here is the puzzle. For the two shelves to join, their edges must STICK together, but the is a non-stick wrapper whose job is to keep surfaces from sticking. So before the shelves can adhere, the periderm over the MEE must be cleared at exactly the right moment. Just before the shelves touch, the periderm cells over the MEE round up and are shed; then the two bare MEE layers press together and adhere, intercalating into a single shared layer down the , the . The genes that build a proper periderm (including the IRF6 program) control whether this clearing happens on cue, and if periderm is faulty, surfaces stick in the wrong places or will not adhere where they should, and fails.
Explore (work the model before reading on)
- What is the name of the on the -facing edge of the shelf?
- What is the , and what is its normal job?
- What happens to the over the MEE just before the shelves touch?
- Why is a non-stick a PROBLEM at the one spot where the shelves need to stick? Explain the conflict in your own words.
- Predict what would happen to the if the over the MEE did NOT clear away on time. Is that something we can confirm from Mateo's outside, or only add to the list of possible causes?
Guided notes
The shelf edge, layer by layer
- The is a flat protective surface layer that normally keeps embryonic surfaces from ____.
- For , the over the MEE must first be ____ (cleared / shed) at the right time and place.
From two edges to one seam
- Once the is gone, the two bare MEE layers adhere at the ____ () and intercalate into one layer.
- That single shared layer is the ____ (MES).
The non-stick then must-stick switch
- The switch is controlled by the gene program (____ and partners) that differentiates the .
- If that program is off or faulty, surfaces stick where they should not or fail to adhere where they should, and the ____.
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
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: Annotate a labeled tissue diagram of the shelf edge: label, in order from outside in at the moment of touching, periderm (being shed), MEE, the forming MES at the midline, and mesenchyme. Then write one sentence explaining why the periderm has to go first, and add to Mateo's chart: "Act 3 begins, shelves adhere into a seam."
- Wrote my Claim, Evidence, and Reasoning exit ticket.
Exit ticket (Claim, Evidence, Reasoning)
- Claim: Two palatal shelves join when their ____ adhere into a single ____.
- Evidence: Before they can adhere, the ____ must be cleared away, because its normal job is to keep surfaces from sticking.
- Reasoning: This matters for Mateo because if the non-stick layer does not clear on time, the shelves ____ and a can result, which adds a possible cause to our list.
| 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 "Annotate a labeled tissue diagram of the shelf edge: label, in order from outside in at the moment of touching, periderm (being shed), MEE, the forming MES at the midline, and mesenchyme. Then write one sentence explaining why the periderm has to go first, and add to Mateo's chart: "Act 3 begins, shelves adhere into a seam."".
- 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 shelves adhere at their medial edges and form one seam down the . But the roof is not truly finished: a wall of cells, the seam, still runs through it. If that wall stays, the two sides are not really one piece. What happens to that wall of cells? We chase that next time, and the answer turns out to be a real scientific argument.