One putatively-conserved commissural cell type is made up of ascending neurons that express the homeobox transcription factor even- skipped (eve/evx) in insects and vertebrates. The analysis and comparison of transcription factor molecular signatures across Bilaterian animals thus represents a powerful approach to put forth and validate hypotheses about the homology of commissural neurons. Transcription factors play a pivotal role in specifying neuronal cell fate.
On the other hand, finding that commissural neurons have acquired the ability to cross the midline convergently would suggest that the blastopore closed independently in the Protosome and Deuterostome lineages. Since commissural neurons require the blastopore to close, finding that homologous neurons are commissural across Bilateria would suggest that the blastopore was closed in Urbilateria. Whether the blastopore was closed in Urbilateria, the last common ancestor of Bilaterians, is an open question. The midline is a structure that is specific to Bilaterian animals and is formed when the blastopore closes. Citation of documents: Please do not cite the URL that is displayed in your browser location input, instead use the DOI, URN or the persistent URL below, as we can guarantee their long-time accessibility.Ĭommissural neurons have their cell body on one side of the body and project their axon across the midline to the other side of the body.
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