We thus suggest evidence that, besides changes in expression domains through alterations in cis-regulation, changes in downstream gene interpretation may also play an important role in the evolution of a snake-like body plan.
Such changes in downstream response to the Hox pattern could, in principle, occur at two levels. First, the response of downstream genes could be altered through changes in cis-regulatory sequences leading to a different response to Hox genes.
Alternatively, changes in Hox coding sequences could lead to the differential activation of target genes.
The contribution of coding sequence evolution to evolutionary modifications has received ample
attention recently (Hoekstra and Coyne, 2007; Wagner and Lynch, 2008) and it has been shown that for instance changes in Ubx coding sequence were essential for changes in invertebrate body plans (Galant and Carroll, 2002; Ronshaugen et al., 2002).