Dendrite branching Flashcards
In developing drosophila, how many of class I-IV sensory neurons are there in each abdominal segment?
3 class I
4 class II
5 class III
3 class IV
Classes (I-IV) of sensory neurons in developing drosophila have different functions, what are these possible functions? (3)
- Proprioception
- Sensing muscle contractions
- Nociception
Why is dendrite branching in drosophila a useful model system?
All the neurons in drosophila have been well-characterized, and they have a very stereotypical fomation
During development, what qualities of drosophila dendrites are stereotypical? (2)
Position and shape
Each class of drosophila sensory neurons (class I - IV) have a distinct…
Dendritic morphology
Class I-IV neurons of the same class have (overlapping/distinct) dendritic fields
Distinct
Why do neurons have distinct dendritic fields?
This simplifies processing: if dendritic fields overlapped too much this would overcomplicate the system
What are fundamental rules that are commonly adhered to during dendrite development
- dendrites within the same neuron spread out by avoiding each other (self-avoidance)
- dendrites of a certain type avoid dendrites of the same type, while dendrites of different types can overlap
What is tiling with respect to dendritic fields?
The distinction between neighbouring dendritic fields between neruons of the same type
Why is coexistence of neurons of difference types necessary?
Need the ability for a given tissue to detect a variety of stimuli
Describe why the leech system was used to study colonization of dendritic fields following ablation
Leech have nicely characterized neurons that have two distinct branches with “mirror-esque” morphology, ablation of one side would demonstrate nicely what happens after
When one part of a dendritic arbor is ablated, does the remaining dendrite react? How?
Ablation of an axon of a minor field allows axons from the major territory to spread into the minor field territory
Starburst amacrine cells are responsible for this property of vision
Directional selectivity
How many kinds of amacrine cells are there?
Upwards of 20 types
Define directional selectivity
Stimuli moving across a receptive field in a particular direction will elicit a neuronal response, but movement in the inverse (negative vector) direction will not elicit the same response
Describe isoneuronal interaction
Interaction among self dendrites
Describe heteroneuronal interaction
Interaction between neighbouring dendrites
What is the key mechanism starburst amacrine cells use to prevent dendrites of the same cell overlapping each other?
Protocadherin recognition
Protocadherins are expressed (2) in single neurons
Stochastically (randomly) and combinatorially
Protocadherins which mediate self-self interactions among dendrites exhibit…
Isoform-specific homophilic adhesion
Do protocadherins always mediate repulsive interactions?
No, sometimes they mediate attractive interactions, this just depends on the cadherin and the context
What is happening in the bottom panel when a specific protocadherin is being knocked out?
See that there is much more overlapping in dendrites, there has been a loss of self-repulsive interactions
What region of the protocadherin protein is being knocked out here?
The variable extracellular domain – all protocadherins “same” now
What is the takeaway of this image?
When these specific isoforms are knocked out, there is no dramatic change in phenotype
No single isoform is necessary for self-avoidance
