Pattern formation Flashcards
What are morphogen gradients
difference in concentrations of a signal from left to right. result in threshold concentrations where at certain levels, cells become a certain cell type
How can patterns be formed with no existing pre-pattern?
by mixing stable equilibrium and diffusion
What are Turing patterns
Stable equilibrium could become unstable solely due to the diffusion of the chemicals involved
Result is very counter-intuitive because diffusion alone levels out all inhomogeneities
What do Turing patterns require?
Must have two opposites - an activator and an inhibitor
Activator should have slower diffusion, inhibitor should have faster diffusion. Causes periodic patterns
How often in chick gastrulation is a new somite formed
1.5 hours
Why does chick somitogensis happen every 1.5 hours?
Shows that animals have a circadian clock - so they can produce a whole number of somites per 24 hours
What is a wavefront
something that freezes a pattern to make it a fixed cycle
What does Lfng do
inhibits notch signalling, by modifying the extracellular domain of notch which affects how cells communicate with each other and causes synchronisation
What happens in mutants with no Lfng
no wave propoagation of gene activity
What chemical creates a morphoegen gradient that activates Lfng
FGF8
What does FGF8 do
inhibits mesp2 in mice and meso1 in chicks. expression of which can only be high when FGF8 is low. mesp2 activates Lfng
What structure is at the tip of the primitive streak
hensens node
What does the primitive streak give rise to
mesenchymal cell that forms the preosomitic mesoderm
What core elements are needed in multilevel modelling
morphogens FGF8 and FGF4
chemotaxis
cell division and differentiation
differential adhesion
What produces FGF4
hensens node and notochord
What produces FGF8
primitive streak
How do FGF8 and FGF4 cause chemotaxis
FGF4 is a chemoattractant
FGF8 is a chemorepellant
What do cells in the hensens node and streak cells differentiate into
hensens node = notochord cells
streak = migrating mesenchymal cells
Do mesenchymal cells and primtiive streak cells adhere to each other?
mesenchymal = do not adhere to eachother and migrate individually
primitive streak = adhere strongly to each other
How does the streak move forward in gastrulation
Cells produce FGF8, are repelled by it
Hensens node produce FGF4 which attracts cells
Causes the streak to move forward
What happens to the streak whne levels of FGF8 drop and FGF4 rise
transition into the presomitic mesoderm
What does a lack of FGF8 in streak retraction result in
oscillations remain. Spatial pattern is created when the presomitic mesoderm is laid down
Results in every 1.5 hours, another somite is formed
Results in a fixed spatial pattern being created
