Fig. 8. Reciprocal cross-species transient expression assays using the Endo16 promoter. GFP reporter constructs were microinjected in a reciprocal cross-species experimental design. Images were captured at three stages of development: mesenchyme blastula (A,D,G,J), gastrula (B,E,H,K), and pluteus larva (C,F,I,L). Microinjection of SpEndo16-GFP into S. purpuratus eggs results in a pattern of GFP expression that recapitulates the results of in situ hybridization of the endogenous gene (Nocente-McGrath et al., 1989; Ransick et al., 1993), and as observed by Yuh et al. (Yuh et al., 1994) in transient expression assays (A-C). Microinjection of LvEndo16-GFP into S. purpuratus eggs results in the same pattern of GFP expression (D-F). Note that it does not drive GFP expression in the hindgut of the pluteus larva (F). Microinjection of SpEndo16-GFP into L. variegatus eggs produces ectopic fluorescence in the SMCs as well their pigment cell derivatives (G-I). As in the reciprocal experiment, no fluorescence is detected in the hindgut of the pluteus larva (I). Microinjection of LvEndo16-GFP into L. variegatus eggs results in a pattern of GFP expression (J-L) that recapitulates the results of in situ hybridization of the endogenous gene as shown in Fig. 2. Fluorescence persists in both the midgut and hindgut of the pluteus larva (L).