Connecting genes, brain and behaviour

Question 1

What genetics approaches in animal models?

Answer 1

Forward genetics
Reverse genetics
Optogenetics

Question 2

A brief outline of how forward genetics approach works

Answer 2

1. Random mutations are induced deliberately
2. The mutagenised animals are crossed with a wild-type strain over several generations
3. In the offspring, we look for the phenotype of interest (Animals are screened for the target phenotype)
4. Animals with the target phenotype are genotyped

So forward genetics is going with the phenotype and then genotyping those animals showing that phenotype to determine how they are genetically different from animals

Question 3

How does Reverse-genetic approach work

Answer 3

Targeted mutations are introduced, and the effect on the phenotype is measured
So we are going from genotype to phenotype

Question 4

In Reverse-genetic approach, how CRISPR-Cas9 introduces targets of mutations

Answer 4

Guide RNA directs the Cas9 protein to the desired DNA sequence, where the Cas9 cuts the DNA.
The random repair process that is initiated when a DNA is cut can
disable the gene or introduce the targeted sequences that would be inserted during repair

Question 5

How does Optogenetics approach work

Answer 5

In this case we are not necessarily interested in understanding the genetic causes of behavior, but rather manipulating these in a genetic level so that we can better understand the link between brain and behavior

Optogenetics uses microbial opsins to excite or inhibit neurons by light

Each responds to light of particular wavelengths

Question 6

In Optogenetics, What is commonly used to introduce the required genetic material (to deliver material into cells)

Answer 6

Adeno-associated virus (AAV), which is a cell-specific promotor sequence that can restrict opsin expression to particular cell types

Question 7

In Optogenetics, The channelrhodopsin-2 (ChR2) pump responds to blue light, and allows positive ions into the cell. this is called __ results in __

Answer 7

Depolarization;

neural excitation

Question 8

In Optogenetics, The halorhodopsin (NpHR) pump responds to yellow light, and allows negative ions into the cell.
this is called __ results in __

Answer 8

Hyperpolarization;

neuronal inhibition

Question 9

In Optogenetics, Light stimulating a particular rhodopsin is delivered through an __

Answer 9

implanted optic fiber

Question 10

In Optogenetics, When particular cells are excited or inhibited, What are we interested in?

Answer 10

What behaviours are evoked or suppressed

Question 11

In combination with an optogenetic system, what does a CRISPR-Cas9 system allow

Answer 11

Light-controlled protein transcription, which means that we can switch on or off the activity of a certain gene in a certain cell by using light

Light-controlled genome editing, meaning DNA can be altered in cells using a combination of CRISPR-Cas9 and optogenetic materials

Question 12

What is the advantage of bioinformatics in animal models?

Answer 12

Genetic associations with behaviour can only hint at the biological pathways involved
Using bioinformatics, we can ‘translate’ a human genetic mutation to target a homologous gene in a model organism

Question 13

What is the advantage of model organism in animal models?

Answer 13

Use CRISPR to introduce that genetic variation into the animal model

Allows more direct measurement at multiple levels that aren’t accessible in the human model:
Structure - using histology to look at when and where cells are developed or expressed;
Function - Electrophysiology to measure neural activity;
Behaviour - verify if we have the same behavior that we thought was associated with that genetic mutation

Question 14

How do we reveal the links in the chain from genetic variant to behavioural phenotype?

Answer 14

imaging genetics

Question 15

How does genes connect to behavior in the case of HTR1A on Amygdala reactivity and Trait anxiety

Answer 15

The functional SNP (rs6295) is situated in the promotor region of HTR1A. It likely affects protein transcription rather than protein structure and it is associated with trait anxiety

G- and G+ are the individuals’ genotypes at that SNP, Individuals with one or two copies of the G allele showed lower trait anxiety than individuals homozygous for the C allele

Question 16

How does genes connect to brain anatomy (structure) in the case of HTR1A on Amygdala reactivity and Trait anxiety

Answer 16

The same HTR1A SNP (rs6295) is associated with serotonin-binding potential

Question 17

How is Binding potential measured in the case of HTR1A on Amygdala reactivity and Trait anxiety

Answer 17

using Positron emission tomography (PET)

Question 18

In the case of HTR1A on Amygdala reactivity and Trait anxiety, Additional copies of the G allele were associated with increased or decreased binding potential? and how?

Answer 18

increased
The G allele impairs the transcriptional repression of the promoter, Causes increased expression of the 5-HT1A receptor
Higher density of receptors leads to higher binding potential

so those without the G allele show low serotonin binding potential, those with the G allele, show high serotonin binding potential

Question 19

In the case of HTR1A on Amygdala reactivity and Trait anxiety, Why is the 5-HT1A receptor an auto-receptor?

Answer 19

It is located at the presynaptic membrane, where it binds neurotransmitters released by the neuron
This is a key part of system for regulating neurotransmiter release

Question 20

How does brain anatomy (structure) connect to brain function in the case of HTR1A on Amygdala reactivity and Trait anxiety

Answer 20

Reduced capacity for regulation of 5-HT release (low binding potential) is associated with increased amygdala reactivity

those with low serotonin binding potential show high amygdala reactivity, those with high serotonin binding potential show low amygdala reactivity

Question 21

How is Amygdala reactivity measured

Answer 21

by comparing BOLD activation in the amygdala between two tasks:
Matching angry or fearful faces vs. matching geometric shapes

Question 22

How does brain function connect to behaviour in the case of HTR1A on Amygdala reactivity and Trait anxiety

Answer 22

Increased amygdala reactivity is associated with increased trait anxiety

Question 23

How does genes connect to brain function in the case of HTR1A on Amygdala reactivity and Trait anxiety

Answer 23

The same HTR1A SNP (rs6295) is associated with amygdala reactivity: Additional copies of the G allele were associated with decreased reactivity

Question 24

How does brain anatomy (structure) connect to behaviour in the case of HTR1A on Amygdala reactivity and Trait anxiety

Answer 24

Increased serotonin-binding potential throughout the brain is associated with lower anxiety

Question 25

Specify the chain from genes to brain structure to brain function to behavior

Answer 25

Presence of the G allele of rs6295 impairs repression of HTR1A transcription This means more transcription, more receptor This leads to increased receptor density, indexed by binding potential In turn, this leads to decreased amygdala reactivity And finally, this predisposes to low anxiety