Developmental expression of synthetic cis-regulatory systems composed of spatial control elements from two different genes.

Synthetic cis-regulatory systems consisting of positively and negatively acting cis-regulatory modules of the Endo16 gene were combined with the lineage-specific regulatory element of the SM50 gene associated with a reporter and injected into eggs of sea urchins. We show here that synthetic cis-regulatory systems consisting of the positive Endo16 regulatory elements linked with the SM50 regulatory element are expressed spatially exactly as the sum of the individual endodermal and skeletogenic expression patterns. In combination, both lineage-specific positive regulatory elements function autonomously. However, addition of the Endo16 regulatory module that represses ectopic skeletogenic expression of Endo16 receptor constructs does not affect expression driven by the SM50 regulatory elements in the same skeletogenic cells. The repression function of this element is thus dedicated to control of the positive spatial output of the Endo16 regulatory system.