An evolutionary & developmental biology lab

Tag: bab

Fine structure of large-effect QTLs

Some of you remember the story of wing dimorphism in wasps from the talk that David Loehlin gave here a year ago.  Here it is finally published:

Evolution of Shape by Multiple Regulatory Changes to a Growth Gene

What I find most interesting about this story is that it adds to the still small collection of cases where a very large effect of a single gene on interspecific divergence is not due to any single large-effect mutation, but rather reflects a cumulative effect of many small(er) mutations accumulating at the same locus.  This is similar to what Ryan Bickel found in bab, and Alistair McGregor in svb.  I suspect the number of similar cases will keep growing.  Surely this is telling us something about the effect of pathway architecture on the course of evolution…

What exactly is an enhancer, and where are its boundaries?

Check out this paper in PLoS Genetics:

Consequences of Eukaryotic Enhancer Architecture for Gene Expression Dynamics, Development, and Fitness

After more than 10 years, Michael Ludwig and his colleagues are still squeezing new insights out of the eve stripe 2 enhancer. Here, they show that sequences flanking the experimentally defined minimal enhancer contribute to the fine-tuning and robustness of gene expression. This helps explain Ryan Bickel’s results that we published last year (Composite Effects of Polymorphisms near Multiple Regulatory Elements Create a Major-Effect QTL). Using a population-genetic approach, Ryan showed that the sequence differences responsible for intraspecific phenotypic variation mapped to regions flanking the known functional elements of the bab locus – enhancer, PRE, and promoter – but not inside these regions.

Aside from the pure scientific knowledge it brings, this paper raises interesting practical questions.  In our search for well-defined minimal enhancers, where should we stop before we go too far? Evolutionary action may well take place outside of the minimal regions sufficient to drive expression in reporter assays. Striking the right balance between functional characterization and evolutionary relevance may be difficult in some cases.

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