PHYLOGENETIC-RELATIONSHIPS AND DEVELOPMENTAL EXPRESSION OF 3 SEA-URCHIN WNT GENES

The Wnt genes comprise a family of secreted glycoproteins involved in cell-cell signaling and pattern formation during the development of a variety of organisms. We have begun to examine Wnt gene expression in sea urchins that exhibit alternative modes of larval development but p roduce similar adults. Here we describe the isolation of five Wnt sequ ences from indirect- and direct-developing sea urchin species using a PCR-based strategy and library screening. Phylogenetic and distance an alyses indicate that the five sequences represent sea urchin Wnt-1, -4 , and -5 orthologs. Wnt-5 sequences were isolated from three sea urchi n species and show a significantly faster rate of evolution than do th eir counterparts in jawed vertebrates. The genomic structure of the Wn t-5 locus was also examined, and its organization is similar to that o f Wnt genes from insects and vertebrates. The temporal expression of a ll three sea urchin Wnt orthologs during sea urchin development was ex amined by RNA gel blots or RNase protection assays. Transcripts from a ll three sea urchin Wnts are detected at various developmental stages of both indirect- and direct-developing species. These data support th e view that sea urchin Wnt genes exhibit many conserved aspects and at least three orthologs are developmentally regulated in both indirect- and direct-developing sea urchin embryos.