NEUR3001 Lecture Notes - Lecture 6: Plasmid, Bioassay, Candidate Gene
Molecular Neural Circuit Formation
1. Sperry’s Eye Rotation Experiment
• Proven Paul Weiss Resonance theory wrong (that claims physical properties of tissue determine nerve
growth, instead of chemical cues)
• Nerve growth in amphibians → neuronal connection regeneration → manipulate connections from injury &
growth → track directional cues
• Demonstrated how neurons find their targets in brain
1.1. Chemo Affinity Hypothesis
Motor programs connect correctly but sequence of motor detection is opposite
∴ Neurons must express specific chemical cues that allow them to recognise their synaptic target (protein-cell
recognition) → Chemo affinity Hypothesis
Retinal
Ganglia target
Severe optic
nerve, invert eye
Nasal cells activated before
temporal cells → eye moves
from left to right
Temporal cells activated
before nasal cells → eye
moves from right to left
Via behavioural assay
i.e. fly in front of newt
i.e. eye looks from
right to left instead
1.2. Retinal Axon Targeting
Indicates that it directs axon terminals to correct location
∴ retinal axons may respond to gradients of chemical cues in tectum → pattern of targeting like topographical map
2. Guidance/Recognition Molecules
2.1. Types
Homophilic vs Heterophilic interactions
Same protein from diff cell membranes bind Diff proteins from diff cell membranes bind
Short range vs Long range
2.2. Organisation
- Signal sequence decides direction → targets ER vesicle to PM → decides if secreted/membrane protein
Usually heterophilic – secreted ligand
interacts with membrane bound receptor
Either homo/heterophilic – membrane bound
cell surface protein that mediate neuron
interaction
2.3. Tested for Binding Activity
I. Aggregation Assay in heterologous cells
- In-vitro assay on cell surface proteins
- Tissue culture cells with cell recognition molecule tested for clumping (in red)
II. ELISA-Based binding assay
• Detection of protein with Ab
2.4. Molecular Functions
Tags HRP Protein
Tags Protein of
Interest
Alkaline
Phosphatase (AP)
Leaves bound
protein
Adhesive (neurons bind)
Neuron projected into brain,
binds to protein → synaptic
matching/layer recognition
Document Summary
Via behavioural assay i. e. fly in front of newt. Via behavioural assay i. e. fly in front of newt i. e. eye looks from right to left instead. Nasal cells activated before temporal cells eye moves from left to right. Temporal cells activated before nasal cells eye moves from right to left. Motor programs connect correctly but sequence of motor detection is opposite. Neurons must express specific chemical cues that allow them to recognise their synaptic target (protein-cell recognition) chemo affinity hypothesis. Indicates that it directs axon terminals to correct location. Retinal axons may respond to gradients of chemical cues in tectum pattern of targeting like topographical map: guidance/recognition molecules. Either homo/heterophilic membrane bound cell surface protein that mediate neuron interaction. Usually heterophilic secreted ligand interacts with membrane bound receptor. Signal sequence decides direction targets er vesicle to pm decides if secreted/membrane protein. Tissue culture cells with cell recognition molecule tested for clumping (in red)
