Hbox1 and Hbox7 are involved in pattern formation in sea urchin embryos

In spite of their potential importance in evolution, there is little inform ation about Hox genes in animal groups that are related to ancestors of deu terostome. It has been reported that only two Hox genes (Hbox1 and Hbox7) a re expressed significantly in sea urchin embryos. Expression of Hbox1 prote in is restricted to the aboral ectoderm, and Hbox7 expression is restricted to oral ectoderm, endoderm and secondary mesenchyme cells in sea urchin em bryos after the gastrula stage. With the aim of gaining insight into the ro le of Hbox1 and Hbox7 in sea urchin development, Hbox1 and Hbox7 overexpres sion experiments were performed. Overexpression of Hbox1 repressed the deve lopment of oral ectoderm, endoderm and mesenchyme cells. On the contrary, o verexpression of Hbox7 repressed the development of aboral ectoderm and pri mary mesenchyme cells. The data suggest that Hbox1 and Hbox7 are expressed in distinct non-overlapping territories, and overexpression of either one i nhibits territory-specific gene expression in the domain of the other. It i s proposed that an important function of both Hbox1 and Hbox7 genes is to m aintain specific territorial gene expression by each one, in its domain of expression, while repressing the expression of the other in this same domai n.