BG16

Question 1

directional patterns

Answer 1

patterns in particular parts

one place rather than another

Question 2

periodic patterns

Answer 2

segments and spots

Question 3

wolpert FFM

Answer 3

1970 french flag model

- cells aquire positional info from morphogens that are secreted from a point source.

Question 4

describe the FFM

Answer 4

morphogen diffuses becomig lower in concentration as it moves away from the source
cells read this gradiet and respond discretely to it
differentiating into different kinds of cells accordingly.

Question 5

what is the fruit fly AP axis a result of

Answer 5

a genetic cascade

Question 6

bicoid mutation drosophila

Answer 6

can cause loss of head to tail patterning etc.

Question 7

bicoid experiments

Answer 7

bicoid gene encodes morphogen responsible for head structures in drosophila
bicoid (-/-) embryos are injected with bicoid mRNA, point of injection forms head structures.
– injection of posterior pole of early cleavage wt embryo with bicoid mrna = head structures at both poles.

Question 8

what is nanos

gradient

Answer 8

posteriror equivalent of bicoid
high gradient posteriorly low anteriorly.
AP gradient of nanos

Question 9

nanos mutants

Answer 9

lack telson - last segment in abdomen

Question 10

caudal and hunch back gradients

Answer 10

both have constant mRNA expression across the embryo however this is truned into a pair of protein gradients
hunchback is highly anteriror, low posterior
caudal vv.

Question 11

hunch back expression regulation

Answer 11

nanons represses translation of hunchback so hunchback mRNA only translated where nanos is low = anteirorly.
bicoid acts as a transcriptional activator of zygotic hunchback causing anterior expression.

Question 12

caudal regualtion

Answer 12

bicoid represses translation of caudal mRNA giving rise to cadual protein gradient.

Question 13

simplist explanation for butterfly eyespots

Answer 13

2D diffusion gradient from morphogenic centre of focus
- cell respond depending on conc gradeitn.
may give rise to diferent sized spots
- non linear FFM.

Question 14

how can you expermientally change spot formation in lepidoptera

Answer 14

1. cauterize (burn away) focus of the morphogen in a caterpillar before pupation - spot fails to form
2. transplant spots to get extra.

Question 15

TF expressed in imaginal diks near site of future spots

Answer 15

distal-less
spallt
engrailed

Question 16

spot mutants in Bicyclus spp

Answer 16

can be interpreted in terms of altering production of or response to such a morphogen.

Question 17

what is the morphogen for spot formation

Answer 17

unknonw
might be wingless
a wnt
dpp
tgf-beta etc.

Question 18

frenchflag model flaws

Answer 18

cant give periodic patterns
repeated patterns
annelids etc.

Question 19

turing model described

Answer 19

model supposed two morphogens with feedback loops
inhibiting or activating themselves and eachother

• when modelled with differential equation under some conditions stationary waves of morphogen conc could be obtained read by cells.

Question 20

turing model

Answer 20

assume have two ligands u and v that interact with each other
du/dt = F(u,v) - duv + Du( changein)u
rate of conc change = production - degredation + diffusion.

same for dv.

Question 21

depending on the parameters of the turing model what states can you get

Answer 21

1. uniform/stationary
2. uniform/oscillating
3. stationary waves with extreme short wave-length
4. oscillatory cases withe extreme short wave lengths
5. oscillatory cases with finite wave length
6. stationary waves with finite wave length = turing pattern.`

Question 22

How the turing model leads to periodic patterns

Answer 22

1. conc of activator is higher in other regions by random fluctuations.
2. by self-enhancing property its concentration increases at centre region followed by an increase of inhibitor in neighbouring regions.
3. as diffusion rate of inhibitor is larger than activator, inhibitor moves to lateral regions
4. depresses the activator function, resulting in decrease of activator conc,
5. decrease causes decrease of inhibitor in wider area
6. so inhibitor conc becomes lower, and then activator becomes dominant
7. leading to local self-activation again
   and cyclical pattern.

Question 23

fruit fly segmentation

Answer 23

segmentation genes are expressed in alternate parasegments
tfs bind to CRE regions in varying strengths chaing expression
- every segment is specified individually
- does not show turing periodic patterning.

mutations are stripe specific.
if turing would kill of all stripes equally.

Question 24

example of turing model

Answer 24

angel and zebrafish
angelfish juveniles stripes change as they grow.
zebrafish have mosaic like arrangement of three pigment cells

Question 25

zebra fish pigment cells

interaction

Answer 25

melanophores - black
xanthophores - yellow
iridiophores - shiny

interaction between melanophores and xanthophores are critical to patterning process.

Question 26

turing model in zebra fish stripes

Answer 26

1. activation of melanophors inhiits xanthophores in the local region.
2. this results in furhter activation of melanophores in this region.
3. inhibition of xanthophores causes decrease of melanophores in distant regions, creating long range inhibitory loop and a stripe.

Question 27

zebra fish mutant stripes

Answer 27

can produce different mutational phenotypes

jaguar: encodes k-channel
leopard: encodes connexin 4.28 involved in gap junctions.

• phenotypes simulated by turing model

Question 28

destruction of pigment and turing model zebrafish

Answer 28

zebrafish stripes dont alter as the fish grows
however if you kill pigmentation cells with a laser beam they will regenerate.
- can also be stimualted using turing models.

Question 29

how are snail patterns generated

Answer 29

by the mantle of snails as it grows.

turing model can generate realistic patterns.

Question 30

snail shell patterns and turing idea.

Answer 30

idea that cells in the mantle produce pigments in response to standing waves of morphogens and that these waves vary as the animal grows, producing patterns.

Question 31

snail patterning mechanism

Answer 31

shell patterns are under neurosecretory control
- mechanistic basis of shell pattern formation as a neurosecretory mech of inhibiton and activation.
sensory cells taste the previously laid pigment patterns that are processed by central ganglion and send to mantle netowrk that controls the pigment secreting cells.

Question 32

turings return?

Answer 32

no strong evidence for turing model in any single system

- any system with activator/inhibitor kinetics = turing process

Question 33

what properties is the neural net model of snail formation based on

Answer 33

spatial lateral inhibition
delayed temporal inhibition.

• neural field equations describe the local pattern of neuron spiking

Question 34

describe the neural net model

Answer 34

1. local activity of excitory neurons induces activity of inhibitiory interneurons in the surrouding tissue.

Question 35

what cant he neural net paramter be used for

Answer 35

can look at the parameters for real shells, estimate and map onto a phylogeny
and the parameter values and hence the patterns of extinct ancestors can then be inferred.