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The problem of development

The problem of development. Eörs Szathmáry (Alpbach 2005). Collegium Budapest. Eötvös University Budapest. What’s this?. Let’s take another look!. Aggregation of the slime mold. The amoebae gather into a focus Individual cells become bipolar. Propagation of the cAMP signal and chemotaxis.

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The problem of development

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  1. The problem of development Eörs Szathmáry (Alpbach 2005) Collegium Budapest Eötvös University Budapest

  2. What’s this?

  3. Let’s take another look!

  4. Aggregation of the slime mold • The amoebae gather into a focus • Individual cells become bipolar

  5. Propagation of the cAMP signal and chemotaxis • Central cell emits a dose of cAMP then it rests for a while • Neighbouring cells creep toward the signal while they also release a dose of cAMP

  6. Formation of Dictyostelium fruiting body • In the slug pre-stalk cells are first • Finally pre-spore cells creep to the front

  7. Why is the problem of development so difficult? • We do not build developing machines: physiology is „easy”, embryology is „difficult”

  8. Preformation versus epigenesis • Homonculus in the sperm • Epigenetics: complexity truly increases

  9. Self-assembly of the virus capsid • Subunits are composed of proteins

  10. The process of aggregation

  11. Formation of the antero-posterior axis of Drosophila

  12. Do the genes programme ontogenesis? • In a sense yes, BUT • A bag of elephant proteins is not an elephant • Structure that self-assemble • Virus particles • The formation of sponges • Limitations of the jigsaw puzzle principle

  13. Wave-like properties of development • Wave forms are largely independent of chemical composition • Animal coat patterns (zebra, tiger, etc.) • BUT altered genes can alter the shape of the elephant • Somehow molecules determine form even if they do not self-assemble • BUT HOW?

  14. The lesser know work of Alan Turing • English mathematician • Breaking of the german code • Creator of the „universal Turing machine” • His relevant paper: Philosophical Transactions of the Royal Society (1952) • What is behind animal coat patterns?

  15. Theory of a chemical standing wave • Two compounds: an activator and an inhibitor • The activator helps its own formation • Inhibitor inhibits the formation of the activator • Both compounds degrade • Inhibitor diffuses much faster

  16. A kémiai állóhullám • In a well-stirred medium both concentrations reach equilibrium • If the solution is not stirred, then a positive fluctuation in activator concentration will enhance itself • Fluctuation is due to chance • Inhibitor concentration also rises, but its higher diffusion rate decrease the amplitude

  17. The coat of a fish • Growth as well as REGENARATION seems to follow a Turing mechanism • Reaction-diffusion systems

  18. Wolpert: a „French flag” A simple model of pattern formation

  19. Positional information and pattern formation • Each person has a specific seat in the stadium • In each seat a specific poster must be shown

  20. Hair patterns in Oncopeltus as indicator of polarity • Hairs point backwards on the cuticule • Removal of segment boundary reverses the direction of hair growth

  21. Development of the chick limb • The zone of polarizing activity (ZPA) directs the formation of the order of digits

  22. The effect of ZPA

  23. Prepattern and consequence • Morphogen is the sonic hedgehog protein

  24. Again the axis of Drosophila

  25. The expression of maternal bicoid mRNA • Both mRNA and protein can be visualized by appropriate compounds

  26. Determination of the 2nd even-skipped (eve) stripe • Bicoid and hunchback proteins activate • Giant and Krüppel inhibit • Not too elegant!

  27. Gene expression and pattern • Combinatorial determination

  28. Vizsgaidőpontok • Január 7, 14, 21, 28 KEDDEK, Szabó József terem 10-12 óra • Január 9, 16, 23 CSÜTÖRTÖKÖK, Szabó József terem

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