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The problem of development
Collegium Budapest Eötvös University Budapest
Eörs Szathmáry (Alpbach 2005)
Aggregation of the slime mold
The amoebae gather into a focusThe amoebae gather into a focus Individual cells become bipolarIndividual cells become bipolar
Propagation of the cAMP signal and chemotaxis
Central cell emits a Central cell emits a dose of cAMP then it dose of cAMP then it rests for a whilerests for a while
Neighbouring cells Neighbouring cells creep toward the creep toward the signal while they also signal while they also release a dose of release a dose of cAMPcAMP
Formation of Dictyostelium fruiting body
In the slug pre-stalk In the slug pre-stalk cells are firstcells are first
Finally pre-spore cells Finally pre-spore cells creep to the frontcreep to the front
SORTing.MOV
Why is the problem of development so difficult?
We do not build developing machines: We do not build developing machines: physiology is „easy”, embryology is physiology is „easy”, embryology is „difficult”„difficult”
Preformation versus epigenesis
HomonculusHomonculus in the in the spermsperm
Epigenetics: Epigenetics: complexity truly complexity truly increasesincreases
Self-assembly of the virus capsid
Subunits are composed of proteinsSubunits are composed of proteins
Do the genes programme ontogenesis? In a sense yes, BUTIn a sense yes, BUT A bag of elephant proteins is not an A bag of elephant proteins is not an
elephantelephant Structure that self-assembleStructure that self-assemble
Virus particlesVirus particles The formation of spongesThe formation of sponges
Limitations of the jigsaw puzzle principleLimitations of the jigsaw puzzle principle
Wave-like properties of development
Wave forms are largely independent of Wave forms are largely independent of chemical compositionchemical composition
Animal coat patterns (zebra, tiger, etc.)Animal coat patterns (zebra, tiger, etc.) BUT altered genes can alter the shape of the BUT altered genes can alter the shape of the
elephantelephant Somehow molecules determine form even if Somehow molecules determine form even if
they do not self-assemblethey do not self-assemble BUT HOW?BUT HOW?
The lesser know work of Alan Turing
English mathematicianEnglish mathematician Breaking of the german Breaking of the german
codecode Creator of the „universal Creator of the „universal
Turing machine”Turing machine” His relevant paper: His relevant paper:
Philosophical Philosophical Transactions of the Royal Transactions of the Royal Society Society (1952)(1952)
What is behind animal What is behind animal coat patterns?coat patterns?
Theory of a chemical standing wave
Two compounds: an Two compounds: an activator and an inhibitoractivator and an inhibitor
The activator helps its The activator helps its own formationown formation
Inhibitor inhibits the Inhibitor inhibits the formation of the activatorformation of the activator
Both compounds degradeBoth compounds degrade Inhibitor diffuses much Inhibitor diffuses much
fasterfaster
A kémiai állóhullám
In a well-stirred medium both concentrations reach In a well-stirred medium both concentrations reach equilibriumequilibrium
If the solution is not stirred, then a positive fluctuation in If the solution is not stirred, then a positive fluctuation in activator concentration will enhance itselfactivator concentration will enhance itself
Fluctuation is due to chanceFluctuation is due to chance Inhibitor concentration also rises, but its higher diffusion Inhibitor concentration also rises, but its higher diffusion
rate decrease the amplituderate decrease the amplitude
The coat of a fish
Growth as well as REGENARATION seems to Growth as well as REGENARATION seems to follow a Turing mechanismfollow a Turing mechanism
Reaction-diffusion systemsReaction-diffusion systems
Positional information and pattern formation
Each person has a Each person has a specific seat in the specific seat in the stadiumstadium
In each seat a specific In each seat a specific poster must be shownposter must be shown
Hair patterns in Oncopeltus as indicator of polarity
Hairs point backwards on the cuticuleHairs point backwards on the cuticule Removal of segment boundary reverses the Removal of segment boundary reverses the
direction of hair growthdirection of hair growth
Development of the chick limb
The zone of polarizing activity (ZPA) directs the The zone of polarizing activity (ZPA) directs the formation of the order of digitsformation of the order of digits
Prepattern and consequence
Morphogen is the Morphogen is the sonic hedgehogsonic hedgehog protein protein
The expression of maternal bicoid mRNA
Both mRNA and Both mRNA and protein can be protein can be visualized by visualized by appropriate appropriate compoundscompounds
Determination of the 2nd even-skipped (eve) stripe
Bicoid and hunchback Bicoid and hunchback proteins activateproteins activate
Giant and Krüppel Giant and Krüppel inhibitinhibit
Not too elegant!Not too elegant!