Fig. 9. Summary of reciprocal cross-species transient expression assays using the Endo16 promoter. Microinjection of the Endo16 promoter into eggs of the same species results in a pattern of GFP expression (green) that recapitulates the results of in situ hybridization (A,D). Microinjection of LvEndo16-GFP into S. purpuratus eggs results in a host-specific pattern of GFP expression (B), while microinjection of SpEndo16-GFP into L. variegatus eggs results in a donor-specific pattern of GFP expression with ectopic fluorescence in the SMCs and their pigment cell derivatives (C). These data indicate that evolutionary changes have arisen both cis and trans to the Endo16 gene. (Arrows indicate hindgut. Arrowheads indicate ectopic fluorescence in the SMCs and pigment cells.)