Molecular genetic insights into deuterostome evolution from the direct-developing hemichordateSaccoglossus kowalevskii

Abstract

AbstractProgress in developmental biology, phylogenomics, and palaeontology over the past five years has made major contributions to a long-enduring problem in comparative biology: the early origins of the deuterostome phyla. A detailed characterization of the early development of the enteropneust hemichordate, Saccoglossus kowalevskii, revealed close developmental genetic similarities between hemichordates and chordates during early body plan formation. The two phyla share close transcriptional and signaling ligand expression patterns during the early development of the anteroposterior and dorsoventral axes, despite large morphological disparity between the body plans. These genetic networks have been proposed to play conserved roles in patterning centralized nervous systems in metazoans, yet likely play conserved roles in patterning the diffusely organized basiepithelial nerve net of the hemichordates. Developmental genetic data are providing a unique insight into early deuterostome evolution, revealing a complexity of genetic regulation previously attributed only to vertebrates. Although these data allow for key insights into the development of early deuterostomes, their utility for reconstructing ancestral morphologies is less certain; morphological, palaeontological and molecular datasets should all be considered carefully when speculating about ancestral deuterostome features.