The developmental hourglass model is applicable to the spinal cord

Abstract

The developmental hourglass model predict that embryonic morphology is most conserved at mid-embryonic stage and diverge at early and late stage. This model is generally considered by whole embryonic level. Here, we demonstrate that the hourglass model is also applicable to the more reduced element, the spinal cord. In the middle of the spinal cord development, dorsoventrally arrayed neuronal progenitor domains are established, which is 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 the 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 has diverged. This study may help understand the molecular basis of the developmental hourglass model.