Lec 12 Teaching Prep: Part 2 - Wolpert vs Turing, Kondo, Cell Migration
2026-05-05 11:26:14 • 7:26
Lecture 12 Teaching Prep Part 2.
Wulpert Versus Turing, the Condo Proof, and the Cell Migration Reveal.
Welcome back.
You are about 14 minutes in.
The Cell Palette TPS just landed.
The students have argued about chromata four stacks and you delivered the reveal that
the Cell Palette doesn't predict the pattern.
Now you set up the central dichotomy of the lecture.
Two ways to make a pattern.
This block is about 13 minutes of class time.
Pace yourself.
Slide 10 is two ways to make a pattern.
Wulpert on the left.
Turing on the right.
This is the conceptual heart of the lecture.
Don't rush.
Three minutes on this slide minimum.
Start with Wulpert.
Wulpert 1969, the French flag model.
A morphogen gradient is set up across a tissue.
By coin in fly embryos, BMP in vertebrae limbs.
Cells read the concentration like reading a thermometer and decide their identity from
where they are.
Identity is positional.
Body coordinates map to color.
Examples butterfly eye spots, fly bristles, vertebrae limb digits.
Pause.
Then Turing.
Turing 1952, reaction diffusion.
Two diffusible signals couple.
Activator promotes itself plus the inhibitor.
Inhibitor diffuses faster.
Periodic instability emerges spontaneously.
There is no pre-existing map.
The pattern is the dynamics.
Examples zebrafish stripes, jaguar rosettes, cyclid bars.
Pause.
Then deliver the synthesis line.
Real animals do both.
Different body regions use different logic in the same animal.
A leopard's body is a Turing canvas.
A leopard's face, where bilateral facial markings live, is positional information.
The pedagogical move on this slide is to make the dichotomy feel like a real binary,
not a minor variant.
Two genuinely different developmental logics.
Both are operating in nature.
Today we tour the evidence for each.
Slide 11 is condo and osse 1995.
Pomechanthus imparata, the emperor angel fish.
This is the single most persuasive slide in the developmental biology side of the course.
Tell it as a discovery story.
As Pomechanthus grows, the number of stripes increases.
If stripes were a fixed pre-pattern, they would just spread apart as the body lengthens.
Instead, new stripes appear by branching.
Exactly what a Turing simulation predicts.
Condo and osse wrote down the equations and matched the stripes-facing dynamics quantitatively.
This is the proof that Turing operates in a real animal.
Forty-three years after Turing's 1952 paper proposed reaction diffusion.
The biology lagged the math by half a century.
Then the biology arrived.
Total time on this slide three minutes.
Don't show the video clip yet.
The next slide brings the Turing math explainer.
This slide is just the result.
Slide 12 is Cheetah Cubs.
Pattern is a trajectory.
Ninety seconds.
This is a quick conceptual move and you do not want it well.
The Cheetah Cubs is born with a long-silvery dorsal mantle that obscures its spots.
The mantle fades over the first three months.
Phenotype emerges.
Same point applies to taper babies, lion cubs, wild boar piglets.
The unifying point is that pattern is dynamic across the lifespan.
A simple Turing parameter set is unlikely to explain this.
There must be temporal modulation of the patterning machinery.
The bridge to the previous slide is intentional.
Condo just showed us pattern rearranging on a growing fish.
Cheetah Cubs show pattern fading on a growing mammal.
Titan is dynamic across the lifespan.
Then advance.
Slide 13 is the minute Earth Turing math explainer.
Two minutes fifteen seconds of video.
Long.
You're spending your video budget here.
Hit play and step back.
The video walks through two diffusing chemicals.
Activator self-promotion.
Inhibitor diffusing faster.
By the time it reaches the chalkboard with the activator inhibitor diagram you should
be silent.
Let the video do the teaching.
Through the video ends, deliver the bridge.
The equations on screen are exactly Turing's 1952 reaction diffusion equations.
The cartoon explainer just walked us through the math.
Now let's see how those equations get extracted from real cells.
Slide 14 is Nakamasu at all 2009 on the left and the Fraunhofer 2013 zebrafish mutant
figure on the right.
The cell rules in zebrafish.
Walk left side first.
Nakamasu used cell ablation in zebrafish to extract the actual cell interaction rules.
Remove melanophores into find regions and watch what happens to surrounding zanthophores.
The result is two rules.
Rule 1.
Short range.
Melanaphore and zanthophore repel each other.
Rule 2.
Long range.
Melanaphore promotes zanthophore survival by a gap junctions.
Watanabe and condo 2015 showed the long range channel is gap junction mediated.
And walk right side.
The Fraunhofer zebrafish image shows wild type at panel A with full stripes.
Panel C through F show Iridiform mutant phenotypes.
Stripes break up into spots in RSE and Shad mutants.
Same Turing system.
One gene perturbed.
Spots not stripes.
The leopard zebrafish story.
Watanabe 2006 is the same logic with a different gene.
Connects in 41.8.
The pedagogical point on this slide is not the math.
It is this.
Cells follow simple local rules.
A single gene change alters the rules.
The global pattern reorganizes.
That is Turing flavor evo-devo in one slide.
Don't try to teach the math.
The video just did it.
Total time 3.5 minutes.
Slide 15 is the zebrafish stripe formation video.
14 seconds looped.
This is the conceptual capstone of the cell roles block.
Hit play.
Loop the clip 3-5 times while you talk.
Tell students what to watch for.
Black cells are melanophores, moving by a me-boyd motility.
Yellow cells are zanthophores, filling the spaces.
They repel each other on contact.
They sustain each other at distance through gap junctions.
After hundreds of cell cell interactions, stripes emerge.
Then deliver the big ideal line.
There is no master plan.
No coordinate system.
Just thousands of cells executing two interaction roles.
The pattern is what emerges when the rules run to equilibrium.
Pause.
The LEC 11 callback on this slide matters.
Last week we met chromatophores as the units of color.
Today we are seeing them as the units of pattern.
Same cells, two functional roles.
Total time 3 minutes.
End of part 2.
You are about 28 minutes in.
On time.
The lecture's central conceptual move has been delivered.
Two ways to make a pattern.
The proof from condo.
The cell rules from Nakamasu.
The live cells doing the work.
Part 3 starts with the reaction diffusion intuition slide and the Murray scaling teaser.