EarlyHoxGene Expression in Echinoderms

Abstract

AbstractBreakages of sequentialHoxexpression in Echinodermata may reflect evolutionary changes in the body plan. We quantifiedHoxgene expression at early larval stages, i.e., blastula at 13 hpf, gastrula at 35 hpf, prism stage at 46 hpf, and echinoplutei at 4 and 9 dpf, in the sea urchin with indirect development,Strongylocentrotus intermedius. The design of specific primers for real-time PCR (q-RT–PCR) forS. intermediuswas performed. At blastula stage, onlySiHox7(medialHoxgroup),SiHox11/13bandSiHox11/13c(posteriorHoxgroup) were expressed. At gastrula and prism stages, the expression ofSiHoxgenes was lower than that in unfertilized eggs. Significant increase in the expression of allSiHoxgenes was observed in 4-day pluteus with further increase ofSiHox1, SiHox8, SiHox9/10, andSiHox11/13bexpression in 9-day pluteus.In other echinoderms, the genes of anteriorHoxgroup are nearly not expressed in the early stages of development. At blastula, gastrula and prism stages, the genes of medialHoxgroup (mainlyHox7andHox8) and posteriorHoxgroup (mainlyHox11/13a, 11/13b, 11/13c) are significantly expressed. This breakage of sequentialHoxexpression in echinoderm ancestors may be caused by loss of metameric gill slits, which are the most important synapomorphy of deuterostomes.