Combination of synthetic regulatory elements underscores the importance of context. (a) Left: a tandem combination of the 5xXhoI-2GH08(L9)/brain and 5x2GH12/notochord concatemers failed to produce any enhancer activity above background. Right: a tandem combination of the 5xXhoI-2GH08(L9)/brain and 5x2CD12/epidermis concatemers resulted in consistent otic lateral line expression. Expression in the forebrain and epidermis was detected inconsistently in a handful of embryos (such as the one shown), but not as intensely as the original concatemer. (b) Injection of a mixture of the 5xXhoI-2GH08(L9)/brain and 5x2GH12/notochord (left) or 5xXhoI-2GH08(L9)/brain and 5x2CD12/epidermis constructs (right) resulted in the expected combinatorial pattern (white arrows). (c) Percentage of embryos expressing in the epidermis, forebrain and notochord for the 5x concatemers individually, as combinations or as a mixture of two constructs. Tandem arrangement of concatemers in the same regulatory element largely failed to reproduce the expression patterns driven by concatemers individually or in a mixture, with the exception of the brain-epidermis combination, which preserved otic lateral line expression.
Smith et al. Genome Biology 2013 14:R72 doi:10.1186/gb-2013-14-7-r72