A global view of gene expression in lithium and zinc treated sea urchin embryos: new components of gene regulatory networks

Background The genome of the sea urchin Strongylocentrotus purpuratus has recently been sequenced because it is a major model system for the study of gene regulatory networks, but embryonic expression patterns for most genes are unknown. Results Using large-scale screens on arrays carrying 50%-70% of all genes, we identified novel territory-specific markers. Our strategy was based on the computational selection of genes differentially expressed in lithium-treated embryos, which form an excess of endomesoderm, and in zinc-treated embryos, in which endomesoderm specification is blocked. Whole-mount in situ hybridization ( WISH) analysis of 700 genes indicates that the apical organ region is eliminated in lithium-treated embryos. Conversely, apical and specifically neural markers are expressed more broadly in zinc-treated embryos, whereas endomesoderm signalling is severely reduced. Strikingly, the number of serotonergic neurons is amplified at least 10-fold in zinc-treated embryos. WISH analysis further indicates that there is crosstalk between the Wnt, Notch and FGF signaling pathways in secondary mesoderm cell specification and differentiation, similar to signalling cascades that function during development of presomitic mesoderm in mouse embryogenesis. We provide differential expression data for more than 4,000 genes and WISH patterns of more than 250 genes and over 2,400 annotated WISH images. Conclusions Our results provide tissue-specific expression patterns for a large fraction of the sea urchin genes that have so far not been included in the existing regulatory networks and await functional integration. Furthermore, a first glimpse on the neuron inducing activity of zinc on embryonic development in any organism was uncovered.