Optogenetics 2 Flashcards
What is disruptive technology?
“Disruptive” technology: typically displaces an established technology, ground-breaking.
What do we use to monitor neural activity?
Previously electrophysiology – now genetically encoded fluorescent sensors/indicators
How do we manipulate neural activity?
Previously direct electrical stimulation/sensory stimulation – now optogenetics and chemogenetics
What is a knock-out model?
If DNA is the instruction manual or ‘blueprint’ for an animal then a gene is a specific instruction
The gene is an instruction to manufacture a specific protein
Proteins are the building blocks of cellular function
It has become possible to ‘knock-out’, or ‘knock-in’ specific genes into the DNA of either the whole animal, or specific cells.
‘Knock-out’: inactivate a targeted gene.
What is ciritical in initial evaluation of role of a gene in brain function?
Global knock outs
What are compensation effects?
Give conflictiing results
What is a knock-in model?
Knock-in’: replace original DNA sequence with a modified version, to alter function of coding gene.
What are humanized mutations?
Mouse has a human gene inserted into its genome. Common in research of neurodegenerative diseases.
What is a limitation of global gene manipulations?
Lack of specificity in time and space
This can be fatal
What can we do to overcome lack of specificity in time and space?
Induce or suppress expression of a gene of interest using a cell-type specific promoter to control mutation – only expression in selective cell types
What are common promoter lines for neurons?
CaMKII (calcium/calmodulin-dependent kinase II alpha gene): excitatory neurons in neocortex and hippocampus.
Human synapsin 1
Platelet-derived growth factor beta chain
Can we use promoters to examine sub-types of neurons?
Yes
e.g. VGAT for GABAergic neurons
Can we use promoters to examine non-neuronal cells?
Yes
e.g. GFAP (glial fibrillary acidic protein) for astrocytes.
What is Cre-lox recombination?
Cre recombinase expression is under a celltype-specific promoter (e.g. VGAT)
Cre recombinase recognises loxP sequences and removes genetic material in between two loxP sites
In cells lacking Cre – original function of gene is unchanged
Its used to carry out deletions, insertions, translocations and inversions at specific sites in the DNA of cells
It allows the DNA modification to be targeted to a specific cell type or be triggered by a specific external stimulus
Can combine with expression of reporter gene, e.g. GFP
What has been an important develoment for cre-lox recombinase?
Development of CreER^T2
Can induce expression of cre and induce the expression of the gene your interested in by treating the animal with Tamoxifen
This allows us to have temporal control
What can cre-lox recombinase also be used to express?
GCaMP
ChR2
How can cre-lox recombinase express e.g. GCaMP?
loxP sites flank ‘stop’ sequence- exposure to Cre recombinase leads to expression of gene in selected cells (e.g Ai38 mouse – GCaMP3 is floxed).
What is viral delivery?
DNA packaged into virus for efficient delivery into brain cells
Adeno-associated virus (AAV, non-human pathogen) is commonly used as delivery system in neuroscience
Provide long term transgene expression – expression in chosen cell type due to promoter expression
Why is viral delivery good?
Allows long term expression of the gene of interest
What has been an important development for viral delivery?
Development of AAV serotypes (AAV9, AAV-PHP.B)