Molecular evidence of anteroposterior patterning in adult echinoderms

Abstract

The origin of the pentaradial body plan of echinoderms from a bilateral ancestor is one of the most enduring zoological puzzles. Since echinoderms are defined by morphological novelty, even the most basic axial comparisons with their bilaterian relatives are problematic. Here, we used conserved antero-posterior (AP) axial molecular markers to determine whether the highly derived adult body plan of echinoderms masks underlying patterning similarities with other deuterostomes. To revisit this classical question, we used RNA tomography and in situ hybridizations in the sea star Patiria miniata to investigate the expression of a suite of conserved transcription factors with well-established roles in the establishment of AP polarity in bilaterians. We find that the relative spatial expression of these markers in P. miniata ambulacral ectoderm shows similarity with other deuterostomes, with the midline of each ray representing the most anterior territory and the most lateral parts exhibiting a more posterior identity. Interestingly, there is no ectodermal territory in the sea star that expresses the characteristic bilaterian trunk genetic patterning program. This suggests that from the perspective of ectoderm patterning, echinoderms are mostly head-like animals, and prompts a reinterpretation of the evolutionary trends that made echinoderms the most derived animal group.

A description of the bat star nervous system throughout larval ontogeny

“…Sequences of P. miniata orthologues were obtained by BLAST searches against a P. miniata transcriptome (Formery et al, 2023) and validated by Bayesian inference phylogenetic trees (Supporting Information: Figure ). Amino acid sequences included in the analysis were obtained by BLAST searches and aligned using MUSCLE as implemented in Geneious version 2020.2.4 (Edgar, 2004).…”

Sea cucumbers: an emerging system in evo-devo

“…Despite the remarkable number of studies exploring hox genes, several aspects of their regulatory mechanisms and the evolution of their functions are still unclear [ 48 , 94 ]. Because of the shift from bilateral to pentameric symmetry during their life cycles, echinoderms are exceptional systems to study hox gene evolution [ 28 , 40 , 53 ]. The analysis of hox genomic organization in Strongylocentrotus purpuratus [ 30 ] and more recently in Paracentrotus lividus [ 97 ] has revealed a reorganization of the hox cluster in echinoids, with translocation and inversion of the anterior hox class genes.…”

“…On the other side, data on hox gene expression in sea urchins [ 7 , 13 ], sea lilies [ 64 ] and sand dollars [ 152 ] showed that hox genes are sequentially expressed along the AP axis of the late larval somatocoels. Finally, a recent work on the sea star Patiria miniata highlights the sequential expression of hox genes in the mesoderm and endoderm of the adult body [ 53 ]. Together, these data show that hox genes have a role in the AP patterning of structures present in the echinoderm late larvae and adults while they are not involved, as a group, in the AP patterning of the embryonic stages [ 13 ].…”

Gene regulatory network that shaped the evolution of larval sensory organ in Cnidaria

“…Taking these nested concentric domains of NVE genes, we asked whether these orthologous genes are expressed in a similar pattern along the anterior-posterior axis in other cnidarian groups (96, 97). Using spatial transcriptome, we can only distinguish the expression of a gene enriched in the apical domain or the rest of the body.…”