The developmental hourglass model is applicable to the spinal cord

Abstract

The developmental hourglass model predicts that embryonic morphology is most conserved at the mid-embryonic stage and diverges at the early and late stages. This model is generally considered by whole embryonic level. Here, we demonstrate that the hourglass model is also applicable to a reduced element, the spinal cord. In the middle of spinal cord development, dorsoventrally arrayed neuronal progenitor domains are established, which are conserved among vertebrates. We found that, by comparing the single-cell transcriptomes between mice and zebrafish, V3 interneurons, a subpopulation of the post-mitotic spinal neurons, display divergent molecular profiles. We also found non-conservation of cis-regulatory elements located around the progenitor fate determinants, indicating the rewiring of the upstream gene regulatory network. These results demonstrate that, despite the conservation of the progenitor domains, processes before and after the progenitor domain specification diverged. This study may help understand the molecular basis of the developmental hourglass model.