ORIGIN OF THE METAZOAN BODYPLAN - CHARACTERIZATION AND FUNCTIONAL TESTING OF THE PROMOTER OF THE HOMEOBOX GENE EMH-3 FROM THE FRESH-WATER SPONGE EPHYDATIA-MUELLERI IN MOUSE 3T3 CELLS

Porifera [sponges] represent the lowest metazoan phylum, probably alre ady exisiting prior to the 'Cambrian explosion'. Based on amino acid s equences deduced from cDNAs that code for structural proteins, the mon ophyly of Metazoa was established. Now we analyzed for the first time a promoter of a sponge gene for its activity in a heterologous cell sy stem from higher Metazoa, The promoter of the homeobox gene EmH-3 was cloned and sequenced from a genomic library of the freshwater sponge E phydatia muelleri. For the determination of functional promoter activi ty, transient transfection experiments in mouse NIH 3T3 cells were per formed; the promoter was fused with the luciferase reporter gene. The data revealed that a 401 nt long promoter fragment, comprising several binding elements for metazoan transcription factors, showed the highe st activity, while the 175 bp long promoter segment, comprising solely the TATA- and Cap boxes, showed only 25% of that activity. This resul t demonstrates that the sponge promoter is activated by factors presen t in mammalian cells and supports the view that Porifera, together wit h the other metazoan phyla, are of monophyletic origin.