Fate Specification of Neural Plate Border by Canonical Wnt Signaling and Grhl3 is Crucial for Neural Tube Closure

During gastrulation, neural crest cells are specified at the neural plate border, as characterized by Pax7 expression. Using single-cell RNA sequencing coupled with high-resolution in situ hybridization to identify novel transcriptional regulators, we show that chromatin remodeler Hmga1 is highly expressed prior to specification and maintained in migrating chick neural crest cells. Temporally controlled CRISPR-Cas9-mediated knockouts uncovered two distinct functions of Hmga1 in neural crest development. At the neural plate border, Hmga1 regulates Pax7-dependent neural crest lineage specification. At premigratory stages, a second role manifests where Hmga1 loss reduces cranial crest emigration from the dorsal neural tube independent of Pax7. Interestingly, this is rescued by stabilized ß-catenin, thus implicating Hmga1 as a canonical Wnt activator. Together, our results show that Hmga1 functions in a bimodal manner during neural crest development to regulate specification at the neural plate border, and subsequent emigration from the neural tube via canonical Wnt signaling.

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Draxin acts as a molecular rheostat of canonical Wnt signaling to control cranial neural crest EMT

The Journal of Cell Biology ◽

10.1083/jcb.201709149 ◽

2018 ◽

Vol 217 (10) ◽

pp. 3683-3697 ◽

Cited By ~ 21

Author(s):

Erica J. Hutchins ◽

Marianne E. Bronner

Keyword(s):

Wnt Signaling ◽

Neural Crest ◽

Neural Tube ◽

Epithelial To Mesenchymal Transition ◽

Cranial Neural Crest ◽

Canonical Wnt Signaling ◽

Mesenchymal Transition ◽

Molecular Rheostat ◽

Timing Of Initiation ◽

Canonical Wnt

Neural crest cells undergo a spatiotemporally regulated epithelial-to-mesenchymal transition (EMT) that proceeds head to tailward to exit from the neural tube. In this study, we show that the secreted molecule Draxin is expressed in a transient rostrocaudal wave that mirrors this emigration pattern, initiating after neural crest specification and being down-regulated just before delamination. Functional experiments reveal that Draxin regulates the timing of cranial neural crest EMT by transiently inhibiting canonical Wnt signaling. Ectopic maintenance of Draxin in the cranial neural tube blocks full EMT; while cells delaminate, they fail to become mesenchymal and migratory. Loss of Draxin results in premature delamination but also in failure to mesenchymalize. These results suggest that a pulse of intermediate Wnt signaling triggers EMT and is necessary for its completion. Taken together, these data show that transient secreted Draxin mediates proper levels of canonical Wnt signaling required to regulate the precise timing of initiation and completion of cranial neural crest EMT.

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Effects of Shh and Noggin on neural crest formation demonstrate that BMP is required in the neural tube but not ectoderm

Development ◽

10.1242/dev.125.24.4919 ◽

1998 ◽

Vol 125 (24) ◽

pp. 4919-4930 ◽

Cited By ~ 18

Author(s):

M.A. Selleck ◽

M.I. Garcia-Castro ◽

K.B. Artinger ◽

M. Bronner-Fraser

Keyword(s):

Neural Crest ◽

Sonic Hedgehog ◽

Neural Tube ◽

Neural Crest Cells ◽

Neural Plate ◽

Bmp Signaling ◽

Neural Tube Closure ◽

Dorsal Neural Tube ◽

Neural Ectoderm ◽

Tube Closure

To define the timing of neural crest formation, we challenged the fate of presumptive neural crest cells by grafting notochords, Sonic Hedgehog- (Shh) or Noggin-secreting cells at different stages of neurulation in chick embryos. Notochords or Shh-secreting cells are able to prevent neural crest formation at open neural plate levels, as assayed by DiI-labeling and expression of the transcription factor, Slug, suggesting that neural crest cells are not committed to their fate at this time. In contrast, the BMP signaling antagonist, Noggin, does not repress neural crest formation at the open neural plate stage, but does so if injected into the lumen of the closing neural tube. The period of Noggin sensitivity corresponds to the time when BMPs are expressed in the dorsal neural tube but are down-regulated in the non-neural ectoderm. To confirm the timing of neural crest formation, Shh or Noggin were added to neural folds at defined times in culture. Shh inhibits neural crest production at early stages (0-5 hours in culture), whereas Noggin exerts an effect on neural crest production only later (5-10 hours in culture). Our results suggest three phases of neurulation that relate to neural crest formation: (1) an initial BMP-independent phase that can be prevented by Shh-mediated signals from the notochord; (2) an intermediate BMP-dependent phase around the time of neural tube closure, when BMP-4 is expressed in the dorsal neural tube; and (3) a later pre-migratory phase which is refractory to exogenous Shh and Noggin.

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Hingepoints and neural folds reveal conserved features of primary neurulation in the zebrafish forebrain

10.1101/738161 ◽

2019 ◽

Author(s):

Jonathan M. Werner ◽

Maraki Y. Negesse ◽

Dominique L. Brooks ◽

Allyson R. Caldwell ◽

Jafira M. Johnson ◽

...

Keyword(s):

Central Nervous System ◽

Neural Tube ◽

Neural Plate ◽

Neural Tube Closure ◽

Developmental Studies ◽

Underlying Causes ◽

The Central Nervous System ◽

Neural Tube Development ◽

Fold Formation ◽

Tube Closure

ABSTRACTPrimary neurulation is the process by which the neural tube, the central nervous system precursor, is formed from the neural plate. Incomplete neural tube closure occurs frequently, yet underlying causes remain poorly understood. Developmental studies in amniotes and amphibians have identified hingepoint and neural fold formation as key morphogenetic events and hallmarks of primary neurulation, the disruption of which causes neural tube defects. In contrast, the mode of neurulation in teleosts such as zebrafish has remained highly debated. Teleosts are thought to have evolved a unique pattern of neurulation, whereby the neural plate infolds in absence of hingepoints and neural folds (NFs), at least in the hindbrain/trunk where it has been studied. We report here on zebrafish forebrain morphogenesis where we identify these morphological landmarks. Our findings reveal a deeper level of conservation of neurulation than previously recognized and establish the zebrafish as a model to understand human neural tube development.

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Sonic hedgehog and the molecular regulation of mouse neural tube closure

Development ◽

10.1242/dev.129.10.2507 ◽

2002 ◽

Vol 129 (10) ◽

pp. 2507-2517 ◽

Cited By ~ 8

Author(s):

Patricia Ybot-Gonzalez ◽

Patricia Cogram ◽

Dianne Gerrelli ◽

Andrew J. Copp

Keyword(s):

Sonic Hedgehog ◽

Neural Tube ◽

Hedgehog Signaling ◽

Neural Plate ◽

Neural Tube Closure ◽

Molecular Regulation ◽

Sonic Hedgehog Signaling ◽

Surface Ectoderm ◽

Necessary And Sufficient ◽

Tube Closure

Neural tube closure is a fundamental embryonic event whose molecular regulation is poorly understood. As mouse neurulation progresses along the spinal axis, there is a shift from midline neural plate bending to dorsolateral bending. Here, we show that midline bending is not essential for spinal closure since, in its absence, the neural tube can close by a ‘default’ mechanism involving dorsolateral bending, even at upper spinal levels. Midline and dorsolateral bending are regulated by mutually antagonistic signals from the notochord and surface ectoderm. Notochordal signaling induces midline bending and simultaneously inhibits dorsolateral bending. Sonic hedgehog is both necessary and sufficient to inhibit dorsolateral bending, but is neither necessary nor sufficient to induce midline bending, which seems likely to be regulated by another notochordal factor. Attachment of surface ectoderm cells to the neural plate is required for dorsolateral bending, which ensures neural tube closure in the absence of sonic hedgehog signaling.

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Snx3 is important for mammalian neural tube closure via its role in canonical and non-canonical WNT signaling

Development ◽

10.1242/dev.192518 ◽

2020 ◽

Vol 147 (22) ◽

pp. dev192518 ◽

Cited By ~ 1

Author(s):

Heather Mary Brown ◽

Stephen A. Murray ◽

Hope Northrup ◽

Kit Sing Au ◽

Lee A. Niswander

Keyword(s):

Wnt Signaling ◽

Neural Tube ◽

Neural Tube Closure ◽

Convergent Extension ◽

Sorting Nexin ◽

Mutant Mouse Embryos ◽

Functionally Impaired ◽

Canonical Wnt

ABSTRACTDisruptions in neural tube (NT) closure result in neural tube defects (NTDs). To understand the molecular processes required for mammalian NT closure, we investigated the role of Snx3, a sorting nexin gene. Snx3−/− mutant mouse embryos display a fully-penetrant cranial NTD. In vivo, we observed decreased canonical WNT target gene expression in the cranial neural epithelium of the Snx3−/− embryos and a defect in convergent extension of the neural epithelium. Snx3−/− cells show decreased WNT secretion, and live cell imaging reveals aberrant recycling of the WNT ligand-binding protein WLS and mis-trafficking to the lysosome for degradation. The importance of SNX3 in WNT signaling regulation is demonstrated by rescue of NT closure in Snx3−/− embryos with a WNT agonist. The potential for SNX3 to function in human neurulation is revealed by a point mutation identified in an NTD-affected individual that results in functionally impaired SNX3 that does not colocalize with WLS and the degradation of WLS in the lysosome. These data indicate that Snx3 is crucial for NT closure via its role in recycling WLS in order to control levels of WNT signaling.

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LRP6 exerts non-canonical effects on Wnt signaling during neural tube closure

Human Molecular Genetics ◽

10.1093/hmg/ddt277 ◽

2013 ◽

Vol 22 (21) ◽

pp. 4267-4281 ◽

Cited By ~ 23

Author(s):

Jason D. Gray ◽

Stanislav Kholmanskikh ◽

Bozena S. Castaldo ◽

Alex Hansler ◽

Heekyung Chung ◽

...

Keyword(s):

Wnt Signaling ◽

Neural Tube ◽

Neural Tube Closure ◽

Tube Closure

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Gene activation during early stages of lens induction in Xenopus

Development ◽

10.1242/dev.125.17.3509 ◽

1998 ◽

Vol 125 (17) ◽

pp. 3509-3519 ◽

Cited By ~ 4

Author(s):

C.A. Zygar ◽

T.L. Cook ◽

R.M. Grainger

Keyword(s):

Neural Tube ◽

Gene Activation ◽

Neural Plate ◽

Neural Tube Closure ◽

Gene Products ◽

Optic Vesicle ◽

Determination Process ◽

Tightly Coupled ◽

Anterior Neural Plate ◽

Tube Closure

Several stages in the lens determination process have been defined, though it is not known which gene products control these events. At mid-gastrula stages in Xenopus, ectoderm is transiently competent to respond to lens-inducing signals. Between late gastrula and neural tube stages, the presumptive lens ectoderm acquires a lens-forming bias, becomes specified to form lens and begins differentiation. Several genes have been identified, either by expression pattern, mutant phenotype or involvement in crystallin gene regulation, that may play a role in lens bias and specification, and we focus on these roles here. Fate mapping shows that the transcriptional regulators Otx-2, Pax-6 and Sox-3 are expressed in the presumptive lens ectoderm prior to lens differentiation. Otx-2 appears first, followed by Pax-6, during the stages of lens bias (late neural plate stages); expression of Sox-3 follows neural tube closure and lens specification. We also demonstrate the expression of these genes in competent ectoderm transplanted to the lens-forming region. Expression of these genes is maintained or activated preferentially in ectoderm in response to the anterior head environment. Finally, we examined activation of these genes in response to early and late lens-inducing signals. Activation of Otx-2, Pax-6 and Sox-3 in competent ectoderm occurs in response to the early inducing tissue, the anterior neural plate. Since Sox-3 is activated following neural tube closure, we tested its dependence on the later inducing tissue, the optic vesicle, which contacts lens ectoderm at this stage. Sox-3 is not expressed in lens ectoderm, nor does a lens form, when the optic vesicle anlage is removed at late neural plate stages. Expression of these genes demarcates patterning events preceding differentiation and is tightly coupled to particular phases of lens induction.

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