Connecting genes, brain and behaviour Flashcards
What genetics approaches in animal models?
Forward genetics
Reverse genetics
Optogenetics
A brief outline of how forward genetics approach works
- Random mutations are induced deliberately
- The mutagenised animals are crossed with a wild-type strain over several generations
- In the offspring, we look for the phenotype of interest (Animals are screened for the target phenotype)
- 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
How does Reverse-genetic approach work
Targeted mutations are introduced, and the effect on the phenotype is measured
So we are going from genotype to phenotype
In Reverse-genetic approach, how CRISPR-Cas9 introduces targets of mutations
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
How does Optogenetics approach work
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
In Optogenetics, What is commonly used to introduce the required genetic material (to deliver material into cells)
Adeno-associated virus (AAV), which is a cell-specific promotor sequence that can restrict opsin expression to particular cell types
In Optogenetics, The channelrhodopsin-2 (ChR2) pump responds to blue light, and allows positive ions into the cell. this is called __ results in __
Depolarization;
neural excitation
In Optogenetics, The halorhodopsin (NpHR) pump responds to yellow light, and allows negative ions into the cell.
this is called __ results in __
Hyperpolarization;
neuronal inhibition
In Optogenetics, Light stimulating a particular rhodopsin is delivered through an __
implanted optic fiber
In Optogenetics, When particular cells are excited or inhibited, What are we interested in?
What behaviours are evoked or suppressed
In combination with an optogenetic system, what does a CRISPR-Cas9 system allow
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
What is the advantage of bioinformatics in animal models?
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
What is the advantage of model organism in animal models?
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
How do we reveal the links in the chain from genetic variant to behavioural phenotype?
imaging genetics
How does genes connect to behavior in the case of HTR1A on Amygdala reactivity and Trait anxiety
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
How does genes connect to brain anatomy (structure) in the case of HTR1A on Amygdala reactivity and Trait anxiety
The same HTR1A SNP (rs6295) is associated with serotonin-binding potential
How is Binding potential measured in the case of HTR1A on Amygdala reactivity and Trait anxiety
using Positron emission tomography (PET)
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?
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
In the case of HTR1A on Amygdala reactivity and Trait anxiety, Why is the 5-HT1A receptor an auto-receptor?
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
How does brain anatomy (structure) connect to brain function in the case of HTR1A on Amygdala reactivity and Trait anxiety
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
How is Amygdala reactivity measured
by comparing BOLD activation in the amygdala between two tasks:
Matching angry or fearful faces vs. matching geometric shapes
How does brain function connect to behaviour in the case of HTR1A on Amygdala reactivity and Trait anxiety
Increased amygdala reactivity is associated with increased trait anxiety
How does genes connect to brain function in the case of HTR1A on Amygdala reactivity and Trait anxiety
The same HTR1A SNP (rs6295) is associated with amygdala reactivity: Additional copies of the G allele were associated with decreased reactivity
How does brain anatomy (structure) connect to behaviour in the case of HTR1A on Amygdala reactivity and Trait anxiety
Increased serotonin-binding potential throughout the brain is associated with lower anxiety
Specify the chain from genes to brain structure to brain function to behavior
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
