Asymmetry

Question 1

degree of lateralisation in humans vs animals

Answer 1

brain laterlaisation is universal in aniamls
NS asymmetry in most animals

Question 2

Easiest lateralisation to see

Answer 2

Behavioural- e.g. prey behaviour

Question 3

when were bilaterians lateralised

Answer 3

at least a billion years ago from fossil evidence, harm only on one side of body- attack from one side

Question 4

why is zebrafish model goof for studying asymmetry

Answer 4

epithalamus robsutly asymmetric

transparent brain
High fecundity (produce multiples of), rapid development outside of the mother, available genetic mutants and transgenic tools make the zebrafish particularly well suited to these types of studies

Question 5

which fly model is an emerging model for asymmetry

Answer 5

NS of flies are too symmetrical - drosophilia may be better model

Question 6

why is mouse a bad model for asymmetry?

Experiemental

Answer 6

mouse brain too complex to see asymmetries

Question 7

pineal gland function

Answer 7

releases melatonin for circadian rhythym

Question 8

left-right differences in efferent connectivity

Question 9

Asymmetric afferent innervation by parapineal

Question 9

What do the left and right hanbenular have in common

connections

Answer 9

both have unipolar projections with spiralling axonal terminals

Question 10

the pp is specified at XX and migrates to XX

Answer 10

The parapineal is specified at the midline and migrates to the left

Question 10

L and R specific spiral morphologies of habenular have ..

Answer 10

different axonal terminals:
left habenular have dorsally located tall spirals

right hennualr has more flat ventrally located spirals

Question 11

Which cell type is important for breaking the symmetry

Answer 11

fgf8 - In ace mutants, pp is present but remains at the midline

Question 12

where is fgf8 expressed?

Answer 12

expressed adjacent to the parapineal at the time it initates migration. the cells that will migrate are found just above (in blue) of fgf8

Question 13

what happens if you give an ace mutant a bead of fgf8?

Answer 13

Restores the asymmetry

exgenous midline fgf8 restores parapineal migration direction usally to the left

Question 14

Why is the direction of asymmetry usally to the left in WT and rescued ace mutants

Answer 14

1. bias in fgf8 siganlling (receptor differentially activated on left)
   2.additional siganlling to bias direction (notch)

Question 15

Where are the receptors and ligand for nodal pathway located?

Answer 15

notch recaptor found on both sides of brain

notch ligand found on only LEFT side as are the cell types that respond to nodal signalling.

Question 16

what sort of siganl is notch

Answer 16

DIRECTIONAL BIAS ONLY

Question 17

How do they know nodal is not needed for asymmetry itself?

Answer 17

ablating ntoch still see asymmetry take place but now occurs eqaully on left or right asymmetry so nothc is only for direction.

Question 18

Can fgf8 bias the direction too?

Answer 18

when they add exogenous beads of fgf8 to notch mutants (no notch), they can bias the direction but its more toward the right

Question 19

Overall how does Nodal interact with fgf8

Answer 19

Nodal causes asymmetric activation of fgf8 signalling on the left side more

Question 20

what happemns when you ablate PP cells before migration

Answer 20

Both sides would show right right characteristics- symmetrtic cell with right sided character.

Question 21

what does genetic screening do

Answer 21

unbiased way of investigating brain asymmetry mutants

Question 22

double right sided character happens when x2:

Answer 22

1. ablate parapineal before migration
2. sox1a mutant

Question 23

what mutant is responsible for double left symmetry

Answer 23

Cachd1 mutant neurons on right side will take on left sided character

Question 24

where is the pp in a cachd1 mutant

Answer 24

They are still only on the left but the right side take on left sided character even though they have not seen pp signal

Question 25

what does cachd1 mutants tell use about right sided character

Answer 25

cachd1 is required for the right side to develop right sided character

Question 26

loss of fucntion of cachd1 results in?

Answer 26

symmetric early neurogenesis- so accelerating neurogensis occurs in cachd1 mutants and more likely to differentiate into left sided character, even before normal left sided neurogensis

Question 27

Neurons on which side are born earlier

Answer 27

left side born earlier

Question 28

cachd1 protein structure

Answer 28

transmembrane protein

Question 29

Where is cachd1 expressed?

Answer 29

Protein expressed bilaterally in ventricular zone of neuroepithelium from which habenular neurons are generated

Question 30

Function of cachd1 on left side of brain- ablation experiment

Answer 30

We know its also expressed on left side. They did a pp ablation in a cachd1 mutant- saw left side stays left side and does not become right sided. Shows pp normally blocks cachd1 function to obtain the left sided character.

Question 31

Interaction between pp and cachd1 on left side

Answer 31

To get left sided character- the pp signal inhibits cachd1 fucntion so that left sided character develops. this is also evidenced in a cachd1 + pp mutant on both sides causing both sides to develop left sided character

Question 32

Molecular fucntion of cachd1

Answer 32

Through a reverse transfection screen they found that cachd1 is a FZD7 binding partner

Question 33

which pathway is FZD7 a part of

Answer 33

wnt signalling- roles in regulating cell fate, proliferation, and differentiation

Question 34

what can cachd1 bind to (oxford lab)

Answer 34

1.FZD7 2.Lrp6 (wnt co receptor)

Question 35

how did they show cachd1 and the wnt pathway interact in habenula

Answer 35

Axin mutant have double right sided character

Question 36

why do wnt Axin mutant have double right sided character?

Answer 36

causes wnt to go up and ??

Question 37

cachd1 genetically interacts with XXX

Answer 37

Tcf712 loss of Tcf712 promotes left sided character

Question 38

what happens with lrp6 mutants

Answer 38

symmetric double left phenotype

Question 39

cachd1 gates wnt siganlling and pp signal flips signalling between two states

Answer 39

hypothesis

Question 40

What is the siganl from the pp that cuases left sided character - what was the study done?

Answer 40

the soxa1 mutant has the parapineal there but no signal comes from it, the result is a symmetric doubel sided phenotype (the same as if you ablate pp) this shows soxa1 interaction with pp is really importnat for developing left sided character

Question 41

How is the development of circuit function affected by mutations that distrupt early left/right pattern?

Answer 41

hypothesis for part 2 of lecture

Question 42

what did they use genetically encoded calcium indicators for

Answer 42

to track neruonal activity in brain to connect asymmetry and mutants to behavioural outcome

Question 43

(pt2.) How do the Left and right habenular respond to light and odour?

Answer 43

left habenular neurons respond to mostly to light right habenular neruons respond to mostly odour

Question 44

(pt.2 sensory (light vs odour) induced activity of habenular neruons cna be resolved in IPN

Answer 44

left hb respond mostly to light and stimulate dorsal IPN Right Hb respond msotly to odour and stimualte ventral IPN

Question 45

(pt2.) How asymmetry changes with reverse RL, RR,LL mutants to IPN projection in context of context- light and odour

Answer 45

1.reverse right-left fish: odour more on left, light more on right-BUT IPN TARGETS REMAIN THE SAME 2.Right-Right fish: both respond to mostly to odour and target only ventral IPN for odour 3.Left-Left fish: both respond to mostly to light and target only dorsal IPN for light

Question 46

Pt3. Defining habenular function: dark conditioning assay- draw this out

Answer 46

fish prefer to be on lighter side of chamber and gets trained to avoid the light side because it knows as soon as it goes into that side that side will turn dark. then goes back to test phase and you expect the fish to be reluctnat to spend time in light side (ptsd girl)

Question 47

pt3. what happens when you ablate dorsal habenular

Answer 47

No impairment to dark condtioning assay

Question 48

pt3. what happens when you ablate ventral habenular

Answer 48

impairs place avoidance condition, fish still spond time in dark condition compared to wt and goes back to light quicker than wt.

Question 49

Social behavioural assay for larval zebrafish

Answer 49

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Question 50

loss of hb affects what about social

Answer 50

distrupts exploration state