Notch signaling is a critical initiator of roof plate formation as revealed by the use of RNA profiling of the dorsal neural tube

Abstract

BackgroundThe dorsal domain of the neural tube is an excellent model to investigate the generation of complexity during embryonic development. It is a highly dynamic and multifaceted region being first transiently populated by prospective neural crest (NC) cells that sequentially emigrate to generate most of the peripheral nervous system. Subsequently, it becomes the definitive roof plate (RP) of the central nervous system. The RP, in turn, constitutes a patterning center for dorsal interneuron development. The factors underlying establishment of the definitive RP and its segregation from NC and dorsal interneurons are currently unknown.ResultsWe performed a transcriptome analysis at trunk levels of quail embryos comparing the dorsal neural tube at premigratory NC and RP stages. This unraveled molecular heterogeneity between NC and RP stages, and within the RP itself. By implementing these genes, we asked whether Notch signaling is involved in RP development. First, we observed that Notch is active at the RP-interneuron interface. Furthermore, gain and loss of Notch function in quail and mouse embryos, respectively, revealed no effect on early NC behavior. Constitutive Notch activation caused a local downregulation of RP markers with a concomitant development of dI1 interneurons, as well as an ectopic upregulation of RP markers in the interneuron domain. Reciprocally, in mice lacking Notch activity, both the RP and dI1 interneurons failed to form and this was associated with expansion of the dI2 population.ConclusionsCollectively, our results offer a new resource for defining specific cell types, and provide evidence that Notch is required to establish the definitive RP, and to determine the choice between RP and interneuron fates, but not the segregation of RP from NC.

Completion of neural crest cell production and emigration is regulated by retinoic acid-dependent inhibition of BMP signaling

“…As recently shown (Ofek et al, 2021), there are differences in the gene expression profile between premigratory NC cells and definitive RP cells. We selected a number of RP-specific genes that are not expressed in the dorsal NT during the NC stage and examined the effect of RA downregulation on their expression.…”

“…The copyright holder for this preprint this version posted August 2, 2021. ; https://doi.org/10.1101/2021.08.02.454731 doi: bioRxiv preprint accounts for the end of NC development. Notably, Raldh2 is also synthesized in the RP of mouse embryos (Ofek et al, 2021). Unfortunately, available mutants of Raldh2 are embryonic lethal at about E8.75 (Niederreither et al, 1999), precluding a focal analysis of the transition from NC to RP.…”

“…Second, cofactors of RA such as Crabp1, could change the nature of the cellular response upon late appearance at the RP stage. Together, changes in the molecular landscape between NC and RP stages (Ofek et al, 2021), that partly depend on local RA activity, may alter the nature of the interactions between RA and BMP/Wnt to signal a timely cessation of NC production.…”

“…The copyright holder for this preprint this version posted August 2, 2021. ; https://doi.org/10.1101/2021.08.02.454731 doi: bioRxiv preprint RA is responsible for the loss of sensitivity of dorsal NT progenitors to BMP during the transition from NC to RP In previous studies, we showed that BMP signaling is essential for NC EMT and emigration (Sela-Donenfeld and Kalcheim, 1999). Subsequently, when approaching the RP stage, although BMP is still produced by the nascent RP, the latter becomes refractory to it, likely via downregulation of BMP receptor 1A (Alk3), and upregulation of BMP inhibitory genes (Nitzan et al, 2016;Ofek et al, 2021). The onset of Raldh2 synthesis close to RP development prompted us to hypothesize that RA, locally produced in the dorsal NT, regulates this dynamic cellular behavior vis-a-vis BMP.…”

From Bipotent Neuromesodermal Progenitors to Neural-Mesodermal Interactions during Embryonic Development

“…First, NC cells that actively proliferate, undergo EMT, leave the NT and engage in migration as mesenchymal cells [56,57]. Second, roof plate cells, which exit the cell cycle, regain epitheliality and baso-apical polarity [58,59]. Third, spinal interneurons whose specification and/or differentiation are induced by the roof plate that acts as an organizing center (Section 1.2) [60].…”