Identification of Homologues of the Emh-3 Homeobox-containing Gene in Demosponges

In the present study, we have identified and characterized homologues of the homeoboxcontaining gene EmH-3 from Ephydatia muelleri in three additional freshwater sponges: Eunapius fragilis, Spongilla lacustris and Trochospongilla horrida. They were designated EmH-3Efr, EmH-3Sl and EmH-3Th. They exhibited a great conservation of genomic and amino acid sequences, exon/intron structure and expression patterns with the EmH-3 gene, which strongly suggested that they have the same function in sponge development. Phylogenetic analyses have shown a grouping of E. muelleri and E. fluviatilis, E. fragilis and S. lacustris, T. horrida being outside both groups. They also showed that EmH-3 and its homologues were most closely related to the Tlx/Hox11 family of higher metazoans. They are probably representatives of this family as they display the family-specific signature and, as are the members of this family, are involved in cell multiplication and differentiation.