Genomic tests of body plan transitions from bilateral to pentameric symmetry in Echinoderms

Echinoderms are an exceptional group in bilaterians in that they develop
pentameral adult symmetry from a bilaterally symmetric larva. However, the
genetic basis in evolution and development of this unique transformation
remains to be clarified. Here we report newly sequenced genomes,
developmental transcriptomes, and proteomes of diverse echinoderms
including the green sea urchin (L. variegatus), a sea cucumber (A.
japonicus), and with particular emphasis on progeny of the
earliest-diverged deuterostome, the feather star (A. japonica). We learned
that the last common ancestor of echinoderms retained a well-organized Hox
cluster genes reminiscent of the hemichordate, and had gene sets involved
in endoskeleton development. Further, unlike in other animal groups, the
most conserved developmental stages was not at the body plan establishing
phase, and genes normally involved in bilaterality appear to function in
pentameral axes development. These results enhance our understanding of
the divergence of protostomes and deuterostomes almost 500 mya.