A reinvestigation of some of the tissue movements involved in the formation of the neural tube and the eye/lens system of Triturus alpestris and Xenopus laevis

Development ◽  
1966 ◽  
Vol 16 (3) ◽  
pp. 431-438
Author(s):  
R. S. Lowery
Keyword(s):  
Xenopus Laevis ◽  
Neural Tube ◽  
Subsequent Development ◽  
Neural Plate ◽  
Eye Lens ◽  
Optic Vesicle ◽  
Lens System ◽  
Lens Development ◽  
Triturus Alpestris ◽  
Optic Cup

Since the beginning of the century the generally accepted scheme of eye/lens development has been that proposed by Spemann (1901) and later confirmed by numerous workers. According to this scheme the two presumptive components of the definitive eye, the optic cup and the lens, are spatially separated at the flat neural plate stage. They later come into apposition as a result of tissue movements which occur during the formation of the neural tube; the optic vesicle then provides an inductive stimulus for the subsequent development of the presumptive lens tissue. Spemann's suggestions concerning the tissue movements involved in the early formation of the eye/lens system do not appear to have been fundamentally questioned until the publication of a number of papers by Chanturishvili (1943, 1949,1958,1959,1962), although the theory of lens induction has been modified by workers such as Liedke (1955), Jacobson (1963) and von Woellwarth (1962).

Gene activation during early stages of lens induction in Xenopus

Development ◽  
1998 ◽  
Vol 125 (17) ◽  
pp. 3509-3519 ◽  
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.

Neural tube closure in Xenopus laevis involves medial migration, directed protrusive activity, cell intercalation and convergent extension

Development ◽  
1999 ◽  
Vol 126 (20) ◽  
pp. 4547-4556 ◽  
Author(s):  
L.A. Davidson ◽  
R.E. Keller
Keyword(s):  
Confocal Microscopy ◽  
Xenopus Laevis ◽  
Neural Crest ◽  
Neural Tube ◽  
Neural Plate ◽  
Neural Cells ◽  
Dorsal Midline ◽  
Cell Movements ◽  
Dorsal Neural Tube

We have characterized the cell movements and prospective cell identities as neural folds fuse during neural tube formation in Xenopus laevis. A newly developed whole-mount, two-color fluorescent RNA in situ hybridization method, visualized with confocal microscopy, shows that the dorsal neural tube gene xpax3 and the neural-crest-specific gene xslug are expressed far lateral to the medial site of neural fold fusion and that expression moves medially after fusion. To determine whether cell movements or dynamic changes in gene expression are responsible, we used low-light videomicroscopy followed by fluorescent in situ and confocal microscopy. These methods revealed that populations of prospective neural crest and dorsal neural tube cells near the lateral margin of the neural plate at the start of neurulation move to the dorsal midline using distinctive forms of motility. Before fold fusion, superficial neural cells apically contract, roll the neural plate into a trough and appear to pull the superficial epidermal cell sheet medially. After neural fold fusion, lateral deep neural cells move medially by radially intercalating between other neural cells using two types of motility. The neural crest cells migrate as individual cells toward the dorsal midline using medially directed monopolar protrusions. These movements combine the two lateral populations of neural crest into a single medial population that form the roof of the neural tube. The remaining cells of the dorsal neural tube extend protrusions both medially and laterally bringing about radial intercalation of deep and superficial cells to form a single-cell-layered, pseudostratified neural tube. While ours is the first description of medially directed cell migration during neural fold fusion and re-establishment of the neural tube, these complex cell behaviors may be involved during cavitation of the zebrafish neural keel and secondary neurulation in the posterior axis of chicken and mouse.

scholarly journals Hallmarks of primary neurulation are conserved in the zebrafish forebrain

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Jonathan M. Werner ◽  
Maraki Y. Negesse ◽  
Dominique L. Brooks ◽  
Allyson R. Caldwell ◽  
Jafira M. Johnson ◽  
...  
Keyword(s):  
Neural Tube ◽  
Time Lapse ◽  
Neural Plate ◽  
Neural Tube Closure ◽  
Developmental Studies ◽  
Underlying Causes ◽  
The Central Nervous System ◽  
Resolution Imaging ◽  
Fold Formation ◽  
Anterior Neural Plate

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 has remained highly debated. Teleosts are thought to have evolved a unique mode of neurulation, whereby the neural plate infolds in absence of hingepoints and neural folds, at least in the hindbrain/trunk where it has been studied. Using high-resolution imaging and time-lapse microscopy, we show here the presence of these morphological landmarks in the zebrafish anterior neural plate. These results reveal similarities between neurulation in teleosts and other vertebrates and hence the suitability of zebrafish to understand human neurulation.

The Xenopus homologue of the Drosophila gene tailless has a function in early eye development

Development ◽  
1998 ◽  
Vol 125 (13) ◽  
pp. 2425-2432 ◽  
Author(s):  
T. Hollemann ◽  
E. Bellefroid ◽  
T. Pieler
Keyword(s):  
Eye Development ◽  
Neural Plate ◽  
Regulatory Function ◽  
Genetic Circuits ◽  
Optic Stalk ◽  
Drosophila Gene ◽  
Ciliary Margin ◽  
Evolutionarily Conserved ◽  
Optic Cup ◽  
Vertebrate Eye

Genetic circuits responsible for the development of photoreceptive organs appear to be evolutionarily conserved. Here, the Xenopus homologue Xtll of the Drosophila gene tailless (tll), which we find to be expressed during early eye development, is characterized with respect to its relationship to vertebrate regulators of eye morphogenesis, such as Pax6 and Rx. Expression of all three genes is first detected in the area corresponding to the eye anlagen within the open neural plate in partially overlapping, but not identical, patterns. During the evagination of the optic vesicle, Xtll expression is most prominent in the optic stalk, as well as in the distal tip of the forming vesicle. In tadpole-stage embryos, Xtll gene transcription is most prominent in the ciliary margin of the optic cup. Inhibition of Xtll function in Xenopus embryos interferes specifically with the evagination of the eye vesicle and, in consequence, Xpax6 gene expression is severely reduced in such manipulated embryos. These findings suggest that Xtll serves an important regulatory function in the earliest phases of vertebrate eye development.

The fate of cells in the tailbud of Xenopus laevis

Development ◽  
2000 ◽  
Vol 127 (2) ◽  
pp. 255-267 ◽  
Author(s):  
R.L. Davis ◽  
M.W. Kirschner
Keyword(s):  
Xenopus Laevis ◽  
Small Groups ◽  
Neural Tube ◽  
Cell Types ◽  
Similar Distribution ◽  
Germ Layer ◽  
Cell Determination ◽  
Multipotent Cells ◽  
Axial Development

The vertebrate tailbud and trunk form very similar tissues. It has been a controversial question for decades whether cell determination in the developing tail proceeds as part of early axial development or whether it proceeds by a different mechanism. To examine this question more closely, we have used photoactivation of fluorescence to mark small neighborhoods of cells in the developing tailbud of Xenopus laevis. We show that, in one region of the tailbud, very small groups of adjacent cells can contribute progeny to the neural tube, notochord and somitic muscle, as well as other identified cell types within a single embryo. Groups averaging three adjacent cells at a later stage can contribute progeny with a similar distribution. Our data suggest that the tailbud contains multipotent cells that make very late germ-layer decisions.

scholarly journals Effects of freezing and activation on membrane quality and DNA damage in Xenopus tropicalis and Xenopus laevis spermatozoa

2017 ◽  
Vol 29 (8) ◽  
pp. 1556 ◽  
Author(s):  
S. Morrow ◽  
J. Gosálvez ◽  
C. López-Fernández ◽  
F. Arroyo ◽  
W. V. Holt ◽  
...  
Keyword(s):  
Xenopus Laevis ◽  
Membrane Damage ◽  
Membrane Integrity ◽  
Subsequent Development ◽  
Xenopus Tropicalis ◽  
Model Organisms ◽  
Sperm Chromatin ◽  
Dna Integrity ◽  
Sperm Cryopreservation ◽  
Sperm Plasma Membrane

There is growing concern over the effect of sperm cryopreservation on DNA integrity and the subsequent development of offspring generated from this cryopreserved material. In the present study, membrane integrity and DNA stability of Xenopus laevis and Xenopus tropicalis spermatozoa were evaluated in response to cryopreservation with or without activation, a process that happens upon exposure to water to spermatozoa of some aquatic species. A dye exclusion assay revealed that sperm plasma membrane integrity in both species decreased after freezing, more so for X. laevis than X. tropicalis spermatozoa. The sperm chromatin dispersion (SCD) test showed that for both X. tropicalis and X. laevis, activated frozen spermatozoa produced the highest levels of DNA fragmentation compared with all fresh samples and frozen non-activated samples (P < 0.05). Understanding the nature of DNA and membrane damage that occurs in cryopreserved spermatozoa from Xenopus species represents the first step in exploiting these powerful model organisms to understand the developmental consequences of fertilising with cryopreservation-damaged spermatozoa.

scholarly journals Bimodal function of chromatin remodeler Hmga1 in neural crest induction and Wnt-dependent emigration

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Shashank Gandhi ◽  
Erica J Hutchins ◽  
Krystyna Maruszko ◽  
Jong H Park ◽  
Matthew Thomson ◽  
...  
Keyword(s):  
Neural Crest ◽  
Neural Tube ◽  
Neural Crest Cells ◽  
Neural Plate ◽  
Chromatin Remodeler ◽  
Lineage Specification ◽  
Dorsal Neural Tube ◽  
Neural Crest Development ◽  
Neural Plate Border ◽  
Canonical Wnt

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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