SB201 Discussion Questions – Stochastic Patterning
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Of the three models for coordination of gene expression that the authors suggest, does
any seem to be favored by the current body of evidence available (perhaps from other
similar studies)? Preferable from the standpoint of robustness to variation?
What is responsible for determining the frequency of Ss allelic expression, and how
stereotyped is this frequency?
In terms of other examples of stochastic patterning, how conserved is this sort of
mechanism?
The cis-regulatory element from the ss(prot-null1) allele up-regulates the expression
frequency of the ss(low freq1) allele, yet in another experiment the ss(low freq1) allele
seemingly down-regulates the expression frequency from ss(wild-type). Might this
alternatively be interpreted as the up-regulation of the ss(low-freq1) allele to a degree
that simply fails to fully match the expression level with homozygous wild-type?
The paper compares the fly eye’s mechanisms to the human eye’s, what might be the
most important reason we see this difference in regulation?
While stochastic mechanisms are cost-effective, are there any other processes that are
even lower cost?
How many step-processes are necessary for stochastic processes to remain controlled?
Under what conditions might more constraints be necessary or unnecessary?
Are there existing molecular examples of the models for coordination of expression
proposed by the authors? Not necessarily in coordination of expression events – but are
there other known instances in which the described “independent decision/tug of war”,
“imposition of decision”, and “contemporaneous compilation of activating and
repressing inputs” occur?
Could position within the developing eye disc affect this process? Do you think the
enhancer/silencers could respond differently depending on relation to the
morphogenetic furrow… do we expect the enhancer/silencers for each allele to respond
in the same way?
Which model(s) for random expression seem most likely to be true? Is one of the
models more commonly found than the others in systems utilizing stochastic
expression? Can we think of any other models?
What might allow one allele to “win” over the other in the tug of war mechanism, or to
be designated the “decider” rather than the naïve allele?
How could you test their various models for interchromosomal communication?
If this goes wrong (i.e. something like the trunc mutant that they used), what is the
effect on vision? Is it detrimental enough to cause a lot of evolutionary pressure for
flies?