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News & ArtsWednesday, March 18, 2009
Science The Mammalian Cell Fate Map
Posted by Jonathan Golob on Wed, Mar 18, 2009 at 2:52 PM
As a part of writing up my PhD thesis, I adapted this figure from Gilbert's Developmental Biology, Fourth Edition: 
(This figure is my own. Click for a much larger version—suitable for printing on an 8.5x11 sheet of paper.)
When I write about embryonic stem cells, I'm often saying something like this:
Making a new mammal requires a single cell to become hundreds of distinct cell types—each with a unique pattern of gene expression that is maintained throughout life.The answer is tremendously complex—much deeper and interesting than “sperm meets egg.” Part of what’s going on in that first trimester is the establishment of all those hundreds of cell types. Complex three-dimensional geometry, a dozen or so of delicate signals, precise timing and luck itself all play into this process. It often fails—in a lab dish or in the gestation of a baby.
This figure lays out, to a rough approximation, our understanding of the various paths a differentiating cell can go down—step-wise—to reach all of those hundreds of cell types found in an adult. Start at the top, at a zygote (a fertilized egg). Trace your way through to all of the organ systems and tissues in the body. Embryonic stem cells, a kind of pluripotent stem cell derived from inner cell mass cells, act like they're near the top of this tree; that is their utility.
The arrows are somewhat deceptive. Each of the branch points is a moment of chance. The developing fetus stacks the deck, but it's still a game of cards. The arrows are more probabilities; they should look like Feynman diagrams, not such beautifully deterministic paths. (That's the answer to the Jeopardy question 'how can this figure be more complicated and daunting?')
Any one of these steps can, and do, go wrong—and whole branches can be omitted by accident—rendering the development a failure.
Where does life begin on that thing? Obviously, there are varying opinions (e.g. the abortion debate) but these could all be labeled in different spots or zones.
You misspelled "ganglia" in Cranial Sensory Ganglia under the Neural Crest category. I'm not trying to nit-pick, I swear. I would hate for your thesis to be rejected because whoever it is that reveiws theses is nuts about ganglia and would be mortally offended by the slip. And it would be all my fault for not pointing it out.
Feel free to use it on Wikipedia.
RonK: From an evolutionary standpoint, it makes a great deal of sense for brain and skin to be, also, closely related. The entire sensory system started as specialized areas of simple organism's outer envelopes. The brain is just an inward growth of these early attempts.
Just wondering.
Pluripotent stem cells are modifications of the ones you show, so that's in the right section, but it's not like they tend to occur naturally, as opposed to actual stem cells.
I really hope the next century is to life sciences/molecular biology/I'm-not-sure-what-the-term-is what the last century was to physics...
It's like they put Byron in a baby and instead of literature, he wrote the bible.
In fact, I've done that where I know how the arrows should be weighted--during our directed differentiation protocol that takes pluripotent stem cells to
1. mesendoderm
2. mesoderm
3. lateral mesoderm
4. splanchnic mesoderm
5. cardiac mesoderm.
In actual development, I'm not sure if anyone knows how the arrows are weighted (or, perhaps even the 'good enough' weighting of the arrows to get offspring.)
The map itself is still under some contention. A fellow scientist here in Seattle--Dr. Horwitz--is using a really clever trick to cleanly define these connections.
God I miss science!
I didn't agree with everything in The Visual Display of Quantitative Information, but it really is a beautiful reference and cohesive graphical style manual for scientific figures.
I share Tufte's disgust for pie charts.
And I share Tufte's disgust for PowerPoint, and the Microsoft-fueled culture of Orwellian stupidity and mendacity:
http://www.units.muohio.edu/technologyan…
Frühlingsgrüße aus Hamburg!
are the tissues descended from those headings more different from the parent than in other areas of the figure? just curious. evo/devo isn't my thing.
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