The mechanism of micromere specification is one of the central issues in sea urchin development. In this study we have identified a sea urchin homologue of ets 1 + 2. HpEts, which is maternally expressed ubiquitously during the cleavage stage and which expression becomes restricted to the skeletogenic primary mesenchyme cells (PMC) after the hatching blastula stage. The overexpression of HpEts by mRNA injection into fertilized eggs alters the cell fate of non-PMC to migratory PMC. HpEts induces the expression of a PMC-specific spicule matrix protein, SM50, but suppresses of aboral ectoderm-specific arylsulfatase and endoderm-specific HpEndo16. The overexpression of dominant negative delta HpEts which lacks the N terminal domain, in contrast, specifically represses SM50 expression and development of the spicule. In the upstream region of the SM50 gene there exists an ets binding site that functions as a positive cis-regulatory element. The results suggest that HpEts plays a key role in the differentiation of PMCs in sea urchin embryogenesis.

Echinoderms (sea urchins, sea stars, brittle stars, sea lilies and sea cucumbers) are a group of diverse organisms, second in number within deuterostome species to only the chordates. Echinoderms serve as excellent model systems for developmental biology due to their diverse developmental mechanisms, tractable laboratory use, and close phylogenetic distance to chordates. In addition, echinoderms are very well represented in the fossil record, including some larval features, making echinoderms a valuable system for studying evolutionary development. The internal relationships of Echinodermata have not been consistently supported across phylogenetic analyses, however, and this has hindered the study of other aspects of their biology. In order to test echinoderm phylogenetic relationships, we sequenced 23 de novo transcriptomes from all five clades of echinoderms. Using multiple phylogenetic methods at a variety of sampling depths we have constructed a well-supported phylogenetic tree of Echinodermata, including support for the sister groups of Asterozoa (sea stars and brittle stars) and Echinozoa (sea urchins and sea cucumbers). These results will help inform developmental and evolutionary studies specifically in echinoderms and deuterostomes in general.

We cloned eight Hox genes (MrHox1, MrHox2, MrHox4, MrHox5, MrHox7, MrHox8, MrHox9/10, and MrHox11/13c) from the sea lily Metacrinus rotundus, a member of the most basal group of the extant echinoderms. At the auricularia stage, before the formation of the pentaradial rudiment, four MrHox genes were expressed sequentially along the anteroposterior (AP) axis in the straightened mesodermal somatocoels in the order MrHox5, MrHox7, MrHox8, and MrHox9/10. The expression of MrHox7 and MrHox8 was detected as early as the hatching stage in the presumptive somatocoel region of the archenteral sac. MrHox5 was expressed in the anteriormost region of the somatocoels, where a stalk-related structure (the chambered organ) forms later. In addition to the mesodermal somatocoels, MrHox7 was expressed in the oral hood ectoderm, which gives rise to the adhesive pit. The expression of four other MrHox genes (MrHox1, MrHox2, MrHox4, and MrHox11/13c) was not detected in any of the larval stages we examined. In comparison with the mesodermal sea urchin Hox genes, the MrHox genes are expressed more posteriorly along the AP (oral-anal) axis than the sea urchin orthologs, implying that the evolution of the eleutherozoans was accompanied by a posteriorization of the larval body. Our study illuminates the possible body plan and Hox expression patterns of the ancestral echinoderm and sheds light on the larval body plan of the last common ancestor of the echinoderms and chordates.

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Suppressed expression of transgenes in vivo is the major obstacle in the gene therapy. For the long-term expression, we utilized a chromatin insulator from sea urchin arylsulfatase (Ars) gene locus (Ars insulator, ArsI), which has been shown to epigenetically regulate gene expression across species. ArsI was able to prevent silencing of the transgene in a myeloid cell line, HL-60, and a murine embryonic stem cell line, CCE, in an orientation-dependent manner, but not in Huh-7, K562 and MCF-7 cells, indicating that the effect of ArsI on gene silencing was cell type dependent. Although anti-silencing effect of ArsI was almost equivalent to that of chicken b-globin insulator, incorporation of ArsI into lentiviral vector had little effect on the virus titer compared with chicken b-globin insulator. Clonal analysis of transduced HL-60 cells revealed that ArsI protects the lentiviral vector from position effects regardless of its orientation. Furthermore, chromatin immunoprecipitation assays revealed that a high acetylation level was observed in the promoter of the insulated vector, whereas that of ArsI was independent of its anti-silencing capacity. In addition to it having little deteriorative effect on the virus titer, the identified anti-silencing effect of ArsI suggested its possibility for application in gene therapy.