Abstract
One of the major goals of the modern study of evodevo is to understand the evolution of gene function across a range of contexts, including sub/neofunctionalization, co-option of genetic modules, and the evolution of morphological novelty. To these ends, comparative studies of gene expression can be useful for constructing hypotheses, but cannot provide direct evidence of functional evolution. Unfortunately, determining endogenous gene function in non-model species is often not an option. Faced with this dilemma, a common approach is to use heterologous expression (HE) in genetically tractable model species as a proxy for functional analyses. Such experiments have important limitations, however, and require caution in the interpretation of their results. How do we dissociate biochemical function from its original genomic context? In the end, what does HE actually tell us? Here, I argue that HE only sheds light on specific types of biochemical conservation, but can be useful when experiments are carefully interpreted.
Highlights
We are essentially performing a site-directed mutagenesis experiment in which we ask whether the sequence differences between your favorite gene (YFG) and its endogenous homolog disrupt the functional roles normally played by the endogenous locus in its own genomic environment
These aspects of gene function may change as the sequence of your favorite gene (YFG) itself evolves
As if this weren’t complicated enough, the actual developmental role played by YFG is the product of all of these primary components interacting with a wide array of cis- and trans-acting phenomena, including the expression patterns of YFG in relation to its co-factors, the epigenetic state of target loci, the position of binding sites within the genome, post-translation regulation of all interacting proteins, etc
Summary
We are essentially performing a site-directed mutagenesis experiment in which we ask whether the sequence differences between YFG and its endogenous homolog disrupt the functional roles normally played by the endogenous locus in its own genomic environment. The commonplace use of the same gene within an organism performing distinct functions in a multitude of tissue reveals why this experiment is generally uninformative with respect to evolutionary history (see Abouheif et al, 1997).” Here, Hodin seeks to highlight the fact that conservation of biochemical interactions within a particular genetic module does not inform on the myriad of ways in which that module can be developmentally deployed.
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