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Biology 467 > Dendrite branching > Flashcards

Dendrite branching Flashcards

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1
Q

In developing drosophila, how many of class I-IV sensory neurons are there in each abdominal segment?

A

3 class I
4 class II
5 class III
3 class IV

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2
Q

Classes (I-IV) of sensory neurons in developing drosophila have different functions, what are these possible functions? (3)

A
  1. Proprioception
  2. Sensing muscle contractions
  3. Nociception
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3
Q

Why is dendrite branching in drosophila a useful model system?

A

All the neurons in drosophila have been well-characterized, and they have a very stereotypical fomation

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4
Q

During development, what qualities of drosophila dendrites are stereotypical? (2)

A

Position and shape

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5
Q

Each class of drosophila sensory neurons (class I - IV) have a distinct…

A

Dendritic morphology

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6
Q

Class I-IV neurons of the same class have (overlapping/distinct) dendritic fields

A

Distinct

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7
Q

Why do neurons have distinct dendritic fields?

A

This simplifies processing: if dendritic fields overlapped too much this would overcomplicate the system

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8
Q

What are fundamental rules that are commonly adhered to during dendrite development

A
  1. dendrites within the same neuron spread out by avoiding each other (self-avoidance)
  2. dendrites of a certain type avoid dendrites of the same type, while dendrites of different types can overlap
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9
Q

What is tiling with respect to dendritic fields?

A

The distinction between neighbouring dendritic fields between neruons of the same type

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10
Q

Why is coexistence of neurons of difference types necessary?

A

Need the ability for a given tissue to detect a variety of stimuli

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11
Q

Describe why the leech system was used to study colonization of dendritic fields following ablation

A

Leech have nicely characterized neurons that have two distinct branches with “mirror-esque” morphology, ablation of one side would demonstrate nicely what happens after

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12
Q

When one part of a dendritic arbor is ablated, does the remaining dendrite react? How?

A

Ablation of an axon of a minor field allows axons from the major territory to spread into the minor field territory

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13
Q

Starburst amacrine cells are responsible for this property of vision

A

Directional selectivity

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14
Q

How many kinds of amacrine cells are there?

A

Upwards of 20 types

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15
Q

Define directional selectivity

A

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

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16
Q

Describe isoneuronal interaction

A

Interaction among self dendrites

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17
Q

Describe heteroneuronal interaction

A

Interaction between neighbouring dendrites

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18
Q

What is the key mechanism starburst amacrine cells use to prevent dendrites of the same cell overlapping each other?

A

Protocadherin recognition

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19
Q

Protocadherins are expressed (2) in single neurons

A

Stochastically (randomly) and combinatorially

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20
Q

Protocadherins which mediate self-self interactions among dendrites exhibit…

A

Isoform-specific homophilic adhesion

21
Q

Do protocadherins always mediate repulsive interactions?

A

No, sometimes they mediate attractive interactions, this just depends on the cadherin and the context

22
Q

What is happening in the bottom panel when a specific protocadherin is being knocked out?

A

See that there is much more overlapping in dendrites, there has been a loss of self-repulsive interactions

23
Q

What region of the protocadherin protein is being knocked out here?

A

The variable extracellular domain – all protocadherins “same” now

24
Q

What is the takeaway of this image?

A

When these specific isoforms are knocked out, there is no dramatic change in phenotype

No single isoform is necessary for self-avoidance

25
Q

What is the takeaway of this image?

A

When only one isoform of protocadherin is being expressed, get extreme self avoidance

Any isoform is sufficient for dendrite self-avoidance

26
Q

Describe how the bar code hypothesis pertains to self-avoidance and protocadherins in the CNS

A

Allows interaction of non-self dendrites and provides high specificity for self-avoidance

Bar code - distinct code which allows neurons to recognize themselves/their neighbours

27
Q

The bar code hypothesis informs how neurons (2)

A

Self avoid
Form synaptic targets and circuits

28
Q

Neuron self-avoidance is mediated by these kinds of molecules in drosophila

A

DsCams

29
Q

DsCams are hypothesized to mediate these kinds of interactions in drosophila

A

Homotypic interactions

30
Q

In drosophila, retinal ON and OFF ganglion cells exhibit what kind of pattern with regards to overlap

A

Tiling: on and off overlap with each other, but they exhibit tiling within their own types

31
Q

What does the Math5 mutant do to ganglion cells?

A

Results in an individual having only about 5% of the normal amount of RGCs – death in 95%

32
Q

How are dendritic fields affected by the Math5 mutant?

A

They are not

33
Q

What does this image tell us about the timing of dendritic repulsion interactions?

A

May be an end-stage fine-tuning mechanism

End stage because they develop their fields independent of interaction from other dendrites – interaction later might cause repulsion (fine-tuning these established fields)

34
Q

Based on the data from this image, is dendritic field formation a cell autonomous or cell non-autonomous process?

A

Cell-autonomous: fields develop without input from other cells

35
Q

What mechanisms regulate dendritic branching? (6)

A
  1. Transcription factor signaling
  2. Secreted proteins/receptor pathways (morphogens, axon guidance molecules)
  3. Cytoskeletal regulators
  4. Secretory pathway proteins (think vesicles)
  5. Cell adhesion molecules
  6. RNA targeting and local translation
36
Q

How many neurons does C. elegans have?

A

302

37
Q

How many somatic cells does C. elegans have?

A

959

38
Q

Describe the central “nerve hub” of C. elegans

A

Has a nerve ring (NR) at its anterior end

39
Q

Describe the hypodermis of C. elegans

A

Kind of like a germ layer, envelops the worm and all the worm’s sensory neurons are embedded within this region

40
Q

Why is PVD a good model neuron to study?

A

There are only 2 of them and their branching is very stereotypical

41
Q

Describe the role of PVD

A

Involved in detection of noxious stimuli: specifically harsh touch (mechanosens) and noxious cold

42
Q

It is common for a lot of mechanosensory neurons in C. elegans to have this property

A

Multisensory

43
Q

The stereotypical branching pattern of PVD is in a “(1)”-like shape

A

Menorah

44
Q

How many levels of branching do PVD neurons undergo?

A

5: 1o, 2o… etc

45
Q

Harsh touch on the quaternary branches of PVD dendrites causes what channels to open?

A

Mechanically-gated epithelial sodium channels: DEG/ENaC on the primary and tertiary branches

46
Q

Do quaternary PVD dendrites contain ion channels

A

Idk maybe but they don’t have ENaC channels which are they only ones we care about in the context of the discussion paper

47
Q

Describe the opening of ENaC channels on 3o and 1o PVD dendrites

A

Stretch opens them allowing the passage of ion channels

48
Q

At what stage during C. elegans development do the PVD neurons appear?

A

The 2nd larval stage

Biology 467 (20 decks)

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