C.elegans Flashcards
how many neurons does a c.elegan have ?
302
how many glial do c.elegans have?
56
what is good about the development in worms for study?
every cell division in development has been documented and the development of every worm is invariant- makes comparing mutants a lot easier
why is a worm good even though it doesn’t have many neurons for nervous system study?
- it has 118 morphological classes of neurons
is the full connectome of the worm known?
yes
is every single neuron in the worm characterised?
yes- they all have names
how many neurons in worms exist in bilateral pairs?
around 1/3
why is knowing the connectome not that helpful?
dont know positive or negative interaction for all etc
what are the main embryology techniques in the worm?
you can do blastomere ablations and manipulations, can do 4D lineaging
what are the main transgenics techniques you can use in the worm?
transcriptional and translational reporters of gene expression and protein localisation, over expression/ rescue
what are the main genetic approaches that are used in the worms?
forward and reverse genetic screens, mutant mapping, genetic dissection of regulatory pathways
what are the molecular biology techniques that can be used in the worm?
RT-PCR, qPCR, FISH, NGS
what is laser ablations?
you can kill specific cells in an embryo
why would you want to do laser ablations? give an example
- laser ablations, you know that Abp cells give rise to certain cells but it is surrounded by Aba and p2- if you ablate these surrounding cells, do you get the same fate or is the cell fate not cell autonomous
why would you want to remove a cell from a blastomere?
to ask about cell intrinsic properties- when alone do its daughter cells change
after isolating a blastomere, what can you do and why would you do this?
isolate ABa and put it next to p2 and see if its fate is turned into a Abp- like fate, this would suggest that p2 induces the Abp fate and can change ABa fate
how can you use 4d lineaging with GFP reporters?
you can label certain cells and then follow how the move
- you can follow expression patterns of genes- follow the lineage and identify in exactly which cells of the lineage this gene is expressed
how can you use 4d lineaging with mutants?
can follow the lineage through an uncover differences in cell lineages of mutants- are cell lost, do they become something else (similar lineage to another cell)?
how can you label all the neutrons in a worm?
you can put GFP downstream of a pan neuronal reporter
how do you inject DNA into a worm to make a transgenic line?
you microinject the DNA contrast into the distal arm of the gonad
why would you use a trancriptional reporter? what are the downsides?
- monitor geen expression
- identify cis-regulatiory analysis (identifyy enhancer regions)
- not all mRNA is translated
- doesn’t show you localisation within the cell
why would you use a translational reporter?
introduce a GFP in frame with your gene
- monitor your gene expression
- monitor protein localisation
- cis-regulatory analysis
- cover-expression or mutant rescue
how can you use translational reporters to understand where a gene is important?
you can produce a trasngeic worm that is a mutant for a gene but has a translational reporter for the gene only expressed in a specific tissue due to the promoter that it is downstream of- this allows you to see when the mutant is rescued dependent on whether the green is required
how can you control when a gene is expressed in a worm?
you can use a translational reporter in a mutant that is downstream of a heat shock promoter
when would you want to use a heat shock promoter?
if you restore the expression in the embryo and you get a rescue and not if you restore late instead, then you know the gene is required n development- can do vice versa
how can you make a transgenic construct in c.elegans?
Inject into gonad - form an “array” (mini-chromosome) that is inherited in a mosaic fashion - can be generated in a week
• For mendelian segregation gamma/uv-irradiate to integrate into the genome- generates double strand breaks to let the DNA pop into the DNA
• Can also bombard (gold particles) directly into genome
what is a fosmid?
5-100 megabases- large piece of DNA- can contain multiple genes- and recombine GFP via HR into the gene of interest and this will allow you to label a gene when you inject this - they generate more complete genetic patterns of reporter
why would you want to make a bi-cistronic fosmid?
so that you can transcriptionally report the expression of a protein in a cell but can also allow the protein to localise to its normal site- you make the GFP be attached to a NLS so that will stay in the nucleus and then after the stop codon of your gene that you are labelling you then put an intercistronic region called SL2- this means that when the gene is transcribed, the protein will do its normal thing and the reporter will go into the nucleus
in order to have one construct transcribed but two different proteins, how can you do this?
you can place an intercistronic region between the two proteins- the first will have a stop codon - this has been shown as SL2 but an IRES can be used too
how can you use transgenics to do promoter analsys to identify cis-regulatory regions- maybe to see which promoter region drives expression in a specific tissue?
you take the upstream region of the gene- hook it up to GFP and make sure that you get expression in the tissue of interest, then you can induce deletions in the promoter - delete a large bit and see you lose expression, then you know that a TF binding site is in there- then you get smaller and smaller each time until you identify which region is important - then you can find the exact region and the sequence- then you can use this and look whether its a motif that is specific for a certain TF
why are transgenic worms good for promoter and cis-regulatory element finding?
-transgenic worms are soda quick and easy to make that you can find an element after making many mutations in the region, very quickly
how do you carry out a classic F2 forward screen in worms?
- use EMS- introduces mutations every 1000 approx.
- so either the eggs or the spam in a hermaphrodite will carry the mutation
- single a herm and it will self fert and produce a het F1 which you can then self fert after being plated
- this will produce 25% homo mutants
how can you use epistasis analysis to order a pathway in worms?
- you mutants that seem to be involved in a similar pathway- for example growth. You can use double mutants which have opposite phenotypes and the double mutant phenotype will normally tell you the downstream component. If you dont have to opposite mutants you can do a gain of function with a loss of function
what types of mutations can you get generally?
- null- no signalling
- loss of function- less signalling
- gain of function- increased signalling
- over expression- increased signalling due to double expression
how can you use SNP-mapping to clone mutated genes?
- use single nucleotide polymorphism
- you performa mapping cross to a polymorphic strain and isolate mutant recombinants
- you analyse the recombination rates of SNP-markers to find out whether the the gene is by looking at which markers (with known positions) do not recombine in the mutants
- you select for homo mutant phenotype in F2- where you’re gene is you will never have had recombination- in this region you will never get the SNPs from th polymorphic strain - you use cloud map and you find where all the reads are the same - no grey SNPS in this region in any of the F2s
how can you do a reverse genetic screen?
use RNAi
what is determinate development?
intrinsic, cell-autonomous, coupled to lineal descent of a cell, no regulation following cell loss