Notch-mediated inhibition of neurogenesis is required for zebrafish spinal cord morphogenesis

Abstract

The morphogenesis of the nervous system requires coordinating the specification and differentiation of neural precursor cells, the establishment of neuroepithelial tissue architecture and the execution of specific cellular movements. How these aspects of neural development are linked is incompletely understood. Here we inactivate a major regulator of embryonic neurogenesis - the Delta/Notch pathway - and analyze the effect on zebrafish central nervous system morphogenesis. While some parts of the nervous system can establish neuroepithelial tissue architecture independently of Notch, Notch signaling is essential for spinal cord morphogenesis. In this tissue, Notch signaling is required to repress neuronal differentiation and allow thereby the emergence of neuroepithelial apico-basal polarity. Notch-mediated suppression of neurogenesis is also essential for the execution of specific morphogenetic movements of zebrafish spinal cord precursor cells. In the wild-type neural tube, cells divide at the organ midline to contribute one daughter cell to each organ half. Notch signaling deficient animals fail to display this behavior and therefore form a misproportioned spinal cord. Taken together, our findings show that Notch-mediated suppression of neurogenesis is required to allow the execution of morphogenetic programs that shape the zebrafish spinal cord.

The E3 Ubiquitin Ligase Mindbomb1 controls zebrafish Planar Cell Polarity

“…Through its ability to promote Delta ligand endocytosis, the E3 Ubiquitin ligase Mindbomb1 plays an essential role in vertebrate Notch receptor activation (Guo et al, 2016). In the course of experiments that were initially designed to study the role of Notch signaling in the morphogenesis of the zebrafish nervous system (Sharma et al, 2019), we realized that embryos injected with a mib1 morpholino (mib1 morphants) present a reduced axial extension at the end of gastrulation that is indicative of defects in embryonic Convergence Extension (CE) movements (Fig.1A). Accordingly, 2 somite stage mib1 morphants present a widening of the notochord, somites and neural plate (Fig.1B).…”

“…Accordingly, 2 somite stage mib1 morphants present a widening of the notochord, somites and neural plate (Fig.1B). The mib1 exon/intron1 splice site morpholino used in these experiments has been previously validated in different studies (Itoh et al, 2003; Sharma et al, 2019). We further confirmed its specificity by showing that the co-injection of a WT mib1 RNA that is not targetable by the morpholino restores axis extension (Fig.1A).…”

“…The mib1 ta52b mutation in the C-terminal Mib1 RING finger domain (RF3, Fig.1C) disrupts the ability of the protein to promote Delta ubiquitination and thereby disrupts Notch signaling (Itoh et al, 2003; Sharma et al, 2019; Zhang, Li, & Jiang, 2007). Axial extension occurs however normally in mib1 ta52b mutants (Fig.1D, Suppl.Fig.1A), raising the question whether Mib1 exerts a Notch-independent function in CE.…”

“…In addition to Mib1, its orthologue Mib2 as well as Asb11, a component of a multisubunit Cullin E3 ligase complex, have been implicated in DSL ligand endocytosis (Sartori da Silva et al, 2010; Zhang, Li, & Jiang, 2007). Nonetheless, mutational analysis in zebrafish failed to confirm a requirement for mib2 in Notch signaling (Mikami et al, 2015) and showed that a mib1 inactivation is sufficient to essentially abolish the expression of a transgenic Notch reporter in the central nervous system (Sharma et al, 2019). These findings identify Mib1 as the major regulator of vertebrate DSL ligand endocytosis.…”

Delta-Notch Signaling: The Long and the Short of a Neuron’s Influence on Progenitor Fates

“…In the cortex, maintenance of Notch signaling in neurons following apical detachment also appears to be required for correct neuronal migration [45,46]. Notch1 signalling is required for the development and maintenance of radial glial cells [46], while reduction of Notch activity was previously shown to disrupt neuroepithelium integrity and increase neurogenesis [47,48]. There is also evidence that N-cadherin-based adherens junctions are critical to maintain tissue integrity and ensure correct rates of proliferation and differentiation [49].…”