ARONOWICZ, J.*; LOWE, C.J.; University of Chicago; University of Chicago: The midbrain-hindbrain gene expression profile in Saccoglossus kowalewskii

The diffuse nervous system of the direct developing hemichordate Saccoglossus kowalewskii shares many of its remarkably complex anterior posterior patterns of developmental gene expression with vertebrates. Recent studies in larvaceans, tunicates and amphioxus indicate that the complex suite of signaling and transcriptional factors that give rise to the midbrain/hindbrain organizer in vertebrates (MHB) have either been partially lost in the cephalochordates and urochordates lineages, or evolved later in chordate evolution along the vertebrate lineage. Our results suggest that much of the genetic regulatory cassette responsible for patterning this critical region of vertebrate neural anatomy evolved very early in deuterostomes, and has been utilized for patterning very different elements of neural organization in vertebrates and hemichordates. The topology of expression of many conserved transcription factors involved in MHB patterning is almost identical between the two groups. Further similarities are found when comparing the expression of signaling molecules such as wnts fgfs and retinoic acid. It appears that the regulatory relationship of genes responsible for patterning the vertebrate MHB have a deep pre-chordate history and have been deployed in taxa with highly divergent neural organization.