Notch signaling is a critical initiator of roof plate formation

Sarah Kagan ¹ Shai Ofek ¹ Sophie Wiszniak ² Markus Tondl ² Quenten Schwarz ² Chaya Kalcheim ¹

¹Department of Medical Neurobiology IMRIC & ELSC, Hebrew University of Jerusalem Israel - Hadassah Medical School, Israel
²Centre for Cancer Biology, University of South Australia and SA Pathology, Australia

The dorsal part of the neural tube is a dynamic region inhabited sequentially by Neural Crest (NC) progenitors, then Roof Plate (RP) cells, and interneurons located ventral to RP. The NC stage is characterized by cell proliferation and delamination, while definitive RP cells become post-mitotic and regain epitheliality. The mechanisms responsible for the transition between NC and RP are yet to be unraveled.
To this end, we performed a comparative transcriptome analysis of RP and premigratory NC cells, respectively. We unraveled more than 1000 differentially expressed genes up- or down-regulated at either stage and discovered novel RP-specific markers.
Among the upregulated genes in RP were components of the Delta-Notch pathway, expressed and active at the ventral border of the RP.
Gain of Notch function within the RP resulted in downregulation of specific RP genes (e.g; Rspo1, Bambi, Raldh2, and draxin), whereas Notch activation in cells adjacent to RP caused ectopic RP properties at the expense of interneuronal traits.
Reciprocally, loss of Notch function in the mouse dorsal neural tube, resulted in downregulation of RP markers, absence of a RP and lack of DI1 interneurons.
Hence, Notch signaling is crucial for determining the ventral limit of the RP adjoining the DI1 domain. Furthermore, it is also sufficient and necessary for RP formation.