Figure 1.

Schematic illustration of the modular cis-regulatory regions of the sea urchin genes Endo16 and SM50, and reporter gene constructs used in this study. VP, vegetal plate; veg₁, veg₁ tier; PMC, primary mesenchyme cells; MG, midgut; Bp, basal promoter. (A) Modules of the 5′ regulatory regions of Endo16 and SM50. Regulatory modules are indicated by differently shaded or hatched boxes. The Endo16 upstream region consists of six regulatory modules. Module A drives early expression in the vegetal plate, the adjoining skeletogenic mesenchyme and ectoderm early in development. The negatively acting modules, DC and E or F, repress gene expression in the skeletogenic mesenchyme and the adjacent veg₁ ectoderm, respectively. Thus, E or F set the upper, and DC the lower, boundary of expression. B is sufficient for midgut-specific late expression, and G helps both A and B in stepping up the amplitude of expression throughout development. In contrast, the SM50 cis-regulatory region is organized in a single module and drives expression exclusively in the autonomously specified skeletogenic mesenchyme. (B) Schematic diagrams of reporter gene constructs. DNA fragments of the Endo16 and SM50 cis-regulatory regions contained in the constructs are shown as boxes. Restriction sites used to clone reporter gene constructs are indicated. Primers are shown as straight arrows, transcription start sites as bent arrows. Cis-regulatory sequences are drawn to scale, but not the CAT fusion gene or the primers. Vector sequences were omitted. (Bar = 100 bp.)