Eph receptor signaling commonly excludes migrating embryonic cells from regions of high ligand density; however, in sea urchin embryos pigmented immunocytes are attracted to regions expressing high levels of Ephrin.
The gene regulatory network controlling directed cell migration in a sea urchin is strikingly similar to a sub-circuit for eye development in Drosophila, suggesting that ancient systems-level controls may be adapted for diverse functions in different animals.
During early embryogenesis of the sea urchin, asymmetrical positioning of the dorsal/ventral organizer relies upon the suppression of organizer activities in dorsal blastomeres by the Hbox12 homeodomain-containing repressor.
Expression of two highly regulated subfamilies of the complex multigene family encoding IL-17 cytokines in the purple sea urchin are sequentially activated in a larval gut-associated inflammation model and modulate downstream gene expression in the gut epithelium.
A gene duplication event has permitted the functional specialization of a homeodomain transcription factor through changes in exon-intron organization and these changes have supported the evolution of a major, phylum-level morphological novelty.