Friday Jan 20, 2012    Lecture Notes for Vertebrate Embryology    Albert Harris


"Positional Information": Wolpert's key concept invented to try to explain anatomy formation.

Each differentiated cell type develops at the right geometric location in the body. (YES!)

Therefore some (chemical) signal must stimulate each cells differentiation. (yes?)

So Wolpert organizes his thinking around finding these chemical signals. (OK?)

"How do embryos develop" becomes "Find the chemical signals that control differentiation".

[He borrows the word "Morphogen" as his name for signals that stimulate differentiation]

Diffusion gradients are hypothesized to be self-repairing spatial patterns of positional information. [Wolpert names this idea: the "French Flag Model"; how to cause a sheet of undifferentiated cells to change into 1/3 red cells, 1/3 white cells, 1/3 blue cells, in the correct spatial pattern & proportions.]

Research in Drosophila (Bicoid gene, Dorsal gene) discovers real gradients that act like that. (yes?)

Eric Wieschaus & Christine Nusslein-Volhard share Nobel Prize for discovering these + > hundred other Drosophila genes that really do control patterned differentiation of embryonic cells

Are Hox genes positional information? (You can't blame people for thinking they must be!)

Is real embryonic development...?

? Basically by positional information except inevitably a little more complicated in some of the details?

?? Not really like P. I., because many of the differences are fundamental & really matter?

A century ago, "the ether" was the key concept for explaining light.

Maybe "Positional Information" will turn out to be as misguided as "the ether" was?

    But Wolpert's enthusiasm attracted hundreds of excellent molecular researchers to study embryological phenomena...

    And gave them terminology and concepts for thinking about how embryos develop. (definitely)

Therefore, so what if his hypotheses have often been mistaken in their details!?


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