Lecture 8; Optogenetics Flashcards
What is optogenetics?
A novel approach to studying synaptic transmission
What three functionalities (uses) can optogenetics be divided into?
1) Reporter
2) Sensory
3) Manipulation / contorl
How can optogenetics function as a reporter?
Reporter;
Static fluorescence label of cells expressing a reporter gene i.e GPCR
How can optogenetics be used as a sensory?
Sensor;
- Dynamic fluorescent sensor of cellular property i.e membrane voltage, Ca2+
- Fluorescent signal is proportional to cellular property
How can optogenetics be used in manipulation / control?
- Photo activation ledas to change in cellular property i.e membrane potential, synaptic vessel release
Describe how a gene is inserted into the genome;
Place gene of interest i.e GFP under a promoter. Promoter could be ubiquitous or cell specific. Therefore end up with GFP only being expressed in cells that youre interested in
What are three methods of gene transfer?
1) Electroporation
2) Stably expressing transgenic animals
3) Viral injection
Describe electroporation
High voltage pulses breakdown plasma membrane allowing entry of a plasmid
- ideal for cell cultures
Describe Stably expressing transgenic animals
- Construct is introduced and incorporated into germ cells
- Colony of expressing animals
Describe viral injection
-package viruses with construct of interest, then transduce the cells
Give an example of a gene used in optogenetics reporting;
GFP
What is GFP origin?
Green Fluorescent Protein
- Isolated from jelly fish
- Genetically modified since then
Allowing for
- Colour variation
- Customised excitation and emission wavelengths
- Improved fluorescence (increased output)
How is GFP used?
- GFP tagged onto other proteins of interest. If GFP is detected in a cell then the tagged invisible protein must also be present
Permits examination of protein : protein interactions
What are the applications of GFP protein?
- Target cell type specific recording / observations (whole cell patch clamp recording)
- Easy visualisation in live tissue (unlike immunihistochemistry that is in fixed tissue)
How does GFP / fluorescence microscopy work?
- Excite GFP with a specific wave length and this will result in the emission (excitation) from the protein of a wavelength lesser than the stimulus
What allows optogenetics to be a biosensor?
We can genetically encode proteins to be sensitive to;
- Voltage
- pH
- Ca (i.e cAMP)
- Protein phosphorylation
Thus fluorescence will occur when certain parameters (levels) are reached
What are the advantages of using optogenetics as a biosensor?
- Cell specific targeting
- Genetic modification of biosensor to suit needs (speed, wavelength emission, kinetics, intensity)
Describe how optogenetics function as a bio sensor;
- FRET based mechanism
or
- i.e Voltage depolarisation causes changes in fluorescent signal. Membrane potential is proportional to fluorescence
What are the current problems with studying synaptic transmission and neural microcircuits?
- Fast (ms)
- Heterogenous (many cell types)
- Highly interconnected (Loops, convergence, divergence)
What are the current methods of studying synaptic transmission and neural microcircuits?
Electrical stimulation;
- Fast (good)
- Spatially imprecise
- Stimulus artefact
Pharmacological stimulation
- Slow
- Dirty, Non-specific actions of drugs
Major problems; Specificity and speed of response
What is the solution to studying synaptic transmission and neural microcircuits?
Light is the ideal control
= single cell activation
How is optogenetics used in control / manipulation when studying synaptic transmission and neural microcircuits?
Light activation of selected genetically modified neurons is precise and rapid.
What are 1-2 advantages of optogenetics? in terms of specificity
1) Gene expression under specific cell type promoter
- Target a single cell type in a population of cells
2) Location of stimulating light point
- Light can be focused to a small definable region, unlike non specific electrical sitmulation
What are 3-5 advantages of optogenetics? in terms of specificty
3) Location of opsin expression (viral vector injection)
4) Different wavelength of excitation or emission
- Multiple optogenetic tools can be used together yet can be distinguished
5) Light has not off target effects