Discussion paper 7 Flashcards
Define a receptive field
The area that encompasses a neuron’s sensory and synaptic inputs
The branching pattern of a dendritic field must be…
Suitable for sampling and processing the signals that converge onto that field
Describe why dendritic fields might need to be flexible
Need to be able to respond or adapt based on experiences (learning)
Self-avoidance with respect to dendritic fields is pretty much synonymous with this term
Tiling
In mammals, where is a location which is a general exception to the tiling rule?
Amacrine cells in the retina – specifically in cells that are responsible for directional sensitivity
What is the broad underlying objective of this paper?
How do different dendrites get their functionally optimal spatial pattern?
Trying to understand the mechanisms underlying dendritic patterning
What is the relevance of seam cells in this paper?
They are partially embedded in the hypodermis: landmark near where PVD dendrite branching occurs
Have cell-specific promoters that can be used to express certain enhancer elements exclusively in these cells – USED TO EXAMINE THE SUFFICIENCY OF GENES EXAMINED IN DIRECTING BRANCHING
What stage during worm development is the focus of this paper?
L4/Young adult worm stage – this is around when 3o and 4o branches start forming
What is the rationale and objective for figure 1?
The authors are looking for mutations which cause defective branching
DMA-1 mutant had been identified by previous studies
DMA-1 is (cytoplasmic/membrane bound)
Membrane-bound
Describe the important “anatomy” of DMA-1
Transmembrane protein
Has a leucine-rich extracellular region, this forms a structural framework for protein-protein interactions
What happens to dendrites which overexpress DMA-1
Overbranching phenotype
What is the main focus of this paper with respect to DMA-1 interactions?
Trying to demonstrate which proteins/ligands interact with it to mediate PVD dendrite branching
What is the model organism of this paper?
C. elegans
Briefly describe the mutagenesis experiments the authors performed to identify mutant genes affecting dendrite branching
Feed organisms mutagen EMS which changes Gs in the organism’s DNA to A’s or A analogs which will base pair with a T, resulting in a 1-base pair change which can have different results
What assay is used to identify missense mutations which impact PVD?
Fluorescently label PVD neurons specifically and examine their branching relative to the wild type
Describe the ser2prom3::myrgfp construct used in figure 1
Promoter specifically for PVD neurons, so this is where gfp construct will be, myr = myristol group which is hydrophobic, so will embed itself in plasma membrane to visualize shape of cells!
What is a key advantage of using C. elegans and gfp constructs for this experiment?
Because C. elegans are so small live imaging can be done with them
What are the most important findings of this figure? (3)
In all mutant phenotypes, failure to form Ts for 3o branches, Ls formed and do not go on to form Ts as in the WT
Failure to form 3o and 4o branches
2o branches disorganized
What is being summarized here?
All mutant phenotypes fail to form Ts where they should be forming Ls – differs significantly from wild type in all cases
ALL MUTANTS SHARE SAME BRANCHING PHENOTYPE – SUGGEST ROLE IN THE SAME PATHWAY
What is the underlying question of this figure?
What is the role of sax-7 in the development of PVD dendrites
What experimental approach is being used in this figure?
Knockout in A, rescue in B using a different promoter
What is the role of the dpy promoter in this figure?
Expresses sax-7 in hypodermal cells
In this experiment, sax-7 is expressed in hypodermal seam cells and in PVD neurons, what are the results of these experiments and what conclusion does this lead the authors to?
Rescue in seam cells is successful, overexpression in PVD neurons does not rescue the mutant phenotype
This means that the role of sax-7 is CELL NON AUTONOMOUS with respect to PVD dendrite branching
When this same experiment (pictured) was performed with mnr-1 (not pictured), what was the result?
Same results as sax-7 experiment: mnr-1 functions cell non autonomously
What is the rationale behind the experiments in this figure?
Expressing sax-7::gfp construct to see where it is normally expressed
panel C: labelling membrane surfaces
panel D: mCherry is being localized to the cytoplasm
What is the takeaway from this figure?
Sax-7 appears to be expressed in hypodermal cells
What is the underlying question of this figure?
How do the sax-7 and mnr-1 mutant dendritic arbor defects arise during development?
What is the experimental approach?
Time-lapse imaging
What is being summarized in this figure?
There is a defect in initiation and maintenance of Ts in all 3 mutants
Lack of stability seems to be a trend but not statistically signficant
As described by this figure, there is a lack of T formation in 3o dendrites due primarily to a lack of (initiation/stabilization)
Initiation
What is the underlying question of this figure?
Is sax-7 sufficient to alter PVD morphology, and if so does it require dma-1 and mnr-1?
What is the experimental approach being used here?
Overexpress sax-7 in seam cells under the control of Pnhr-81 promoter (this is ectopic expression: not normally here)
What kind of experiment is being performed here (loss, gain, correlative)?
Gain of function
What are the most important findings of this figure?
Ectopic expression of sax-7 in seam cells can direct PVD dendrites to seam cells
What is the purpose of doing this experiment in the sax-7 mutant?
Because if you did it in the WT you could have competing sax-7 confounding your results – makes interpretation easier
What happens when the authors perform this experiment in the sax-7-mnr1- double mutant?
Ectopic sax-7 does not retarget dendrites to seam cells
What are the main conclusions of this experiment?
Sax-7 functions non-cell-autonomously to direct PVD dendrites and REQUIRES mrn-1
What is the underlying question of this figure?
Does Dma-1 physically interact with sax-7 and mnr-1?
What is the experimental approach used in this figure?
Do a cell aggregation assay and tag proteins to see if they are colocalized
What are the most important findings of this figure?
The cells only interact if all three (sax-7, mnr-1 and dma-1) are present
Describe the model for interaction based on all the results presented in this paper
PVD neurons which possess dma-1 interact with hypodermal cells expressing sax-7 and mnr-1, which forms an attractive subcellular pattern on which the dendrites of PVD neurons can grow.
