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At least 433 records · Page 24Linked to original sources
PubMed1987

Expression of the proto-oncogene int-1 is restricted to specific neural cells in the developing mouse embryo.

We have used in situ hybridization and computer-aided reconstruction to study the spatial distribution of expression of the mammary tumor proto-oncogene int-1 during mouse embryogenesis. int-1 RNA accumulation is restricted to specific regions of the neural plate and its derivatives between 9 and 14.5 days of development. int-1 RNA accumulates throughout the neural plate at the anterior head folds of the 9 day embryo but only at its lateral tips in more posterior regions. Following neural tube closure, int-1 expression is restricted to specific regions of the dorsal wall of the brain ventricles and spinal cord, the ventral wall of the midbrain and the diencephalon, and the lateral walls of the neuroepithelium at the midbrain-hindbrain junction. These data suggest that int-1 has a role in the early stages of central nervous system development in the mouse embryo.

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PubMed2004

Induction of the neural crest and the opportunities of life on the edge.

The neural crest is a multipotent population of migratory cells unique to the vertebrate embryo. Neural crest arises at the lateral edge of the neural plate and migrates throughout the embryo to give rise to a wide variety of cell types including peripheral and enteric neurons and glia, craniofacial cartilage and bone, smooth muscle, and pigment cells. Here we review recent studies that have addressed the role of several signaling pathways in the induction of the neural crest. Work in the mouse, chick, Xenopus, and zebrafish have shown that a complex network of genes is activated at the neural plate border in response to neural crest-inducing signals. We also summarize some of these findings and discuss how the differential activation of these genes may contribute to the establishment of neural crest diversity.

Animals↗
PubMed1999

Comparative expression of the mouse Sox1, Sox2 and Sox3 genes from pre-gastrulation to early somite stages.

Whole mount in situ hybridisation was used to study the embryonic expression of the mouse HMG box-containing genes Sox1, Sox2 and Sox3 between 6.5 and 9.0 days post coitum (dpc). Sox2 and Sox3 are expressed in the epiblast and extraembryonic ectoderm of the egg cylinder, becoming restricted to the prospective neural plate and chorion at the onset of gastrulation. Sox3 is upregulated in the posterior ectoderm during late streak and neural plate stages and is concomitantly downregulated in the chorion. Sox1 transcripts are first detected in the neural fold ectoderm at the headfold stage. During early somitogenesis, all three genes are expressed in the neuroectoderm, and Sox2 and Sox3 are also expressed in the primitive streak ectoderm, gut endoderm and prospective sensory placodes.

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PubMed1994

Electron microscopic study of the development of amphioxus, Branchiostoma belcheri tsingtauense: the neurula and larva.

The later development of Asian amphioxus was investigated by scanning and transmission electron microscopy (SEM and TEM). The age ranged from 10.5 hr (the early neurula) to 48 hr after fertilization (the larva with two gill-slits). This period was divided into 6 stages; the neurula (N) 1, 2, 3, and the larva (L) 1, 2, 3. At stage N1, the lateral edge of the flattened neural plate became stratified and the superficial layer separated from the deeper one to spread over the neural plate toward the median line where they fuse randomly with each other. The notochord and the mesoderm were formed by folding from the dorsomedian and the dorsolateral wall of the archenteron during stages N1 to N2. At stage N3, a typical triploblastic embryo was formed, consisting of the definitive ectoderm, neural tube, notochord, endoderm and mesoderm (the wall of the coelom). Ultrastructurally, paramyosin fibrils in the notochordal cells and myofibrils in the muscle cells were found at stage L1. After stage L1, the anteroposterior differentiation took place and the formation of the larval organs progressed. Self-feeding larval life was established at stage L3 when the larva acquired the mouth and two gill-slits.

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PubMed1999

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

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.

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PubMed1999

cSix4, a member of the six gene family of transcription factors, is expressed during placode and somite development.

We describe the expression pattern of cSix4, a chick homologue of the murine Six4/AREC3 gene. cSix4 transcripts are detected at gastrula stages in the blastoderm surrounding the developing axial midline. As the neural plate begins to form cSix4 mRNA is detected in a crescent-shaped band, which surrounds the anterior developing neural plate and corresponds to the presumptive placode region. This expression is maintained in all the placodes (olfactory, optic, neural and otic) as they develop but with different characteristics. Further, abundant expression of cSix4 was localised to the paraxial mesoderm and the entire developing somites, becoming restricted first to their dorsal portion, then to the dermomyotome and finally to the myotome. cSix4 expression is maintained in the developing and adult muscular tissue. Additional sites of cSix4 expression are the presumptive and developing limb buds, the notochord, trigeminal ganglia, cells of the spinal cord, particularly the motor neurones, the dorsal root ganglia, the neural retina, as well as the epithelial component of the developing kidney.

Animals↗
PubMed2005

To proliferate or to die: role of Id3 in cell cycle progression and survival of neural crest progenitors.

The neural crest is a unique population of mitotically active, multipotent progenitors that arise at the vertebrate neural plate border. Here, we show that the helix-loop-helix transcriptional regulator Id3 has a novel role in cell cycle progression and survival of neural crest progenitors in Xenopus. Id3 is localized at the neural plate border during gastrulation and neurulation, overlapping the domain of neural crest induction. Morpholino oligonucleotide-mediated depletion of Id3 results in the absence of neural crest precursors and a resultant loss of neural crest derivatives. This appears to be mediated by cell cycle inhibition followed by cell death of the neural crest progenitor pool, rather than a cell fate switch. Conversely, overexpression of Id3 increases cell proliferation and results in expansion of the neural crest domain. Our data suggest that Id3 functions by a novel mechanism, independent of cell fate determination, to mediate the decision of neural crest precursors to proliferate or die.

Animals↗
PubMed1995

Localized BMP-4 mediates dorsal/ventral patterning in the early Xenopus embryo.

Mesoderm is initially induced in the amphibian embryo by events that occur in the early cleavage stages prior to the midblastula transition (MBT) and morphogenesis. These inductive interactions establish the mesoderm at the equator and create a distinction between the dorsal and the ventral regions. After the MBT, zygotic factors pattern the mesoderm and induce the neuroectoderm on the dorsal side of the embryo. Most previous studies have focused on the effects of signals originating in the dorsal mesoderm. We show that BMP-4 transcripts are localized to the ventral side of the gastrula embryo and provide evidence that localized expression of BMP-4 is important for regulating the expression of mesodermal and neural genes. We show that ectopic expression of BMP-4 inhibits the formation of dorsal and lateral mesoderm and reduces the size of the neural plate. Elimination of BMP-4 signaling with a dominant-negative BMP receptor expands the lateral mesoderm and neural plate without expanding the expression of genes along the dorsal midline. These results suggest that BMP-4 may act to oppose the action of dorsalizing signals and neural-inducing signals that originate in the dorsal organizer region. We suggest that BMP-4 may have an analogous role to the Drosophila gene, dpp, in dorsal/ventral pattern formation.

Animals↗
PubMed2006

Xenopus Xotx2 and Drosophila otd share similar activities in anterior patterning of the frog embryo.

Despite the obvious anatomical differences between the fly and the vertebrate body plans, several genes involved in their development are largely conserved. In this work we provide evidence that overexpression of the Drosophila orthodenticle (otd) gene in Xenopus laevis has a similar effect to that of its homolog Xotx2. Injections of otd mRNA in whole embryos lead to posterior truncations and to induction of ectopic cement glands, similar to Xotx2 injections. In animal cap assays, otd, like Xotx2, is able to activate the cement gland marker XAG and to suppress the expression of the epidermal marker XK81. Finally, as assayed by Einsteck transplantation assays, otd, like Xotx2, is able to respecify a tail/trunk organizer to a head organizer. In this work we also show that Xotx2 and otd share molecular functions that regulate early regional specification of the Xenopus anterior neural plate. Gain-of-function experiment targeting low doses of either otd or Xotx2 mRNAs in the neural plate promote reduction of Xrx1 and Xbf1 expression domain; no changes are observed for the anterior mesodermal marker Xgsc, the dorsal diencephalic marker Xbh1, and the midbrain/hindbrain marker Xen2. otd/Xotx2 inhibition activity of Xrx1 and Xbf1 expression is consistent with the strong inhibition of Xfgf8 expression in the anterior neural ridge observed upon otd/Xotx2 mRNA injection.

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PubMed1999

Control of neurogenesis--lessons from frogs, fish and flies.

Two types of genes activated by neural inducers have been identified, those that lead to the activation of proneural genes and those that limit the activity of these genes to specific domains in the neural plate. The analysis of these genes has begun to fill gaps in our understanding of events that lead from neural induction to the generation of neurons within three longitudinal columns in the Xenopus and zebrafish neural plate.

Animals↗
PubMed1995

A role for HGF/SF in neural induction and its expression in Hensen's node during gastrulation.

It was previously shown (Roberts, C., Platt, N., Streit, A., Schachner, M. and Stern, C. D. (1991) Development 112, 959-970) that grafts of Hensen's node into chick embryos enhanced and maintain expression of the L5 carbohydrate in neighbouring epiblast cells, and that antibodies against L5 inhibit neural induction by such a graft. We now show that L5 is initially widely expressed in the epiblast, but as neural induction proceeds it gradually becomes confined to and up-regulated in the early neural plate. L5 can therefore be considered as a marker for cells that are competent to respond to neural induction. We also show that Hepatocyte Growth Factor/Scatter Factor (HGF/SF) promotes the expression of L5 by extraembryonic epiblast in collagen gels after overnight culture. Explants cultured for several days in the presence of HGF/SF, as well as explants of prospective neural plate, can differentiate into cells with neuronal morphology expressing neuronal markers. To investigate whether HGF/SF is expressed in the chick embryo at appropriate stages of development, we produced specific cDNA probes and used them for in situ hybridization. We find that at the primitive streak stage, HGF/SF is expressed specifically in Hensen's node. We therefore propose that HGF/SF plays a role during the early steps of neural induction, perhaps by inducing or maintaining the competence of the epiblast to respond to neural inducing signals.

Animals↗
PubMed1998

Combinatorial Gli gene function in floor plate and neuronal inductions by Sonic hedgehog.

Within the developing vertebrate nervous system, it is not known how progenitor cells interpret the positional information provided by inducing signals or how the domains in which distinct groups of neural cells differentiate are defined. Gli proteins may be involved in these processes. In the frog neural plate, we have previously shown that the zinc finger transcription factor Gli1 is expressed in midline cells and mediates the effects of Shh inducing floor plate differentiation. In contrast, Gli2 and Gli3 are expressed throughout the neural plate except for the midline. Here, it is shown that Gli3 and Shh repress each other whereas Gli2, like Gli1, is a target of Shh signaling. However, only Gli1 can induce the differentiation of floor plate cells. In addition, Gli2 and Gli3 repress the ectopic induction of floor plate cells by Gli1 in co-injection assays and inhibit endogenous floor plate differentiation. The definition of the floor plate domain, therefore, appears to be defined by the antagonizing activities of Gli2 and Gli3 on Gli1 function. Because both Gli1 and Gli2 are induced by Shh, these results establish a regulatory feedback loop triggered by Shh that restricts floor plate cells to the midline. We have also previously shown that the Gli genes induce neuronal differentiation and here it is shown that there is specificity to the types of neurons the Gli proteins induce. Only Gli1 induces Nkx2.1/TTF-1(+) ventral forebrain neurons. Moreover, Gli2 and Gli3 inhibit their differentiation. In contrast, the differentiation of spinal motor neurons can be induced by the two ventrally expressed Gli genes, Gli1 and Gli2, suggesting that Gli2 directly mediates induction of motor neurons by Shh. In addition, Gli3 inhibits motor neuron differentiation by Gli2. Thus, combinatorial Gli function may pattern the neural tube, integrating positional information and cell type differentiation.

Animals↗
PubMed2005

Neural induction: old problem, new findings, yet more questions.

During neural induction, the embryonic neural plate is specified and set aside from other parts of the ectoderm. A popular molecular explanation is the 'default model' of neural induction, which proposes that ectodermal cells give rise to neural plate if they receive no signals at all, while BMP activity directs them to become epidermis. However, neural induction now appears to be more complex than once thought, and can no longer be fully explained by the default model alone. This review summarizes neural induction events in different species and highlights some unanswered questions about this important developmental process.

Animals↗
PubMed1999

Head induction in the chick by primitive endoderm of mammalian, but not avian origin.

Different types of endoderm, including primitive, definitive and mesendoderm, play a role in the induction and patterning of the vertebrate head. We have studied the formation of the anterior neural plate in chick embryos using the homeobox gene GANF as a marker. GANF is first expressed after mesendoderm ingression from Hensen's node. We found that, after transplantation, neither the avian hypoblast nor the anterior definitive endoderm is capable of GANF induction, whereas the mesendoderm (young head process, prechordal plate) exhibits a strong inductive potential. GANF induction cannot be separated from the formation of a proper neural plate, which requires an intact lower layer and the presence of the prechordal mesendoderm. It is inhibited by BMP4 and promoted by the presence of the BMP antagonist Noggin. In order to investigate the inductive potential of the mammalian visceral endoderm, we used rabbit embryos which, in contrast to mouse embryos, allow the morphological recognition of the prospective anterior pole in the living, pre-primitive-streak embryo. The anterior visceral endoderm from such rabbit embryos induced neuralization and independent, ectopic GANF expression domains in the area pellucida or the area opaca of chick hosts. Thus, the signals for head induction reside in the anterior visceral endoderm of mammals whereas, in birds and amphibia, they reside in the prechordal mesendoderm, indicating a heterochronic shift of the head inductive capacity during the evolution of mammalia.

Animals↗
PubMed1998

Timing and mechanisms of mesodermal and neural determination revealed by secondary embryo formation in Cynops and Xenopus.

We examined the timing and mechanisms of mesodermal and neural determination in Cynops, using the secondary embryo induced by transplantation of the prechordal endomesoderm. Two unique approaches were used: one was to observe gastrulation movements induced by the graft, and the other to measure the volumes of formed tissues. Transplanted graft pulled host animal cap cells inside to form a new notochord and other mesoderm of the secondary embryo, showing determination of mesoderm during gastrulation. The graft attained a certain width beneath the host ectoderm and moved near to the animal pole of the host by late gastrula, and a neural plate, which had a similar width to the graft, was formed covering the graft. The volume of neural tissues of the secondary embryo at tail-bud stages was about half that of the normal embryo, while the volumes of notochord were comparable in each case. These data suggest that prechordal endomesoderm, rather than notochord, determines the limit of neural plate in the overlying ectoderm. Similar dorsal grafts were transplanted at early gastrula in Xenopus but did not form well developed secondary embryos, demonstrating that the timing and mechanisms of mesoderm formation in Xenopus are different from those in Cynops.

Animals↗
PubMed1980

Duplication of the spinal cord: a discussion of the possible embryogenesis of diplomyelia.

The possible embryogenesis of diplomyelia is discussed in the context of the current understanding of neurulation. The mechanisms of normal development of the neural tube differ from one region to another, so the initial step in development of diplomyelia will probably depend on the location of the lesion. In the cranial portion of the neural tube, abnormal folding of the neural plate is most likely to be responsible for the formation of supernumerary lumina. In the intermediate transitional region, the neural plate diminishes as the contribution from the end bud increases, so errors might originate in either or both of these structures. In the caudal region of the embryo, the neural tube is established by canalization of the solid medullary cord, so diplomyelia in this region is most likely to stem from faulty canalization. Once the sub-populations of neural cells have been established, their subsequent physical separation appears to be due to changes in the region between the adjacent lumina, for example enlargement of intercellular spaces and degeneration of neural cells.

Animals↗
PubMed1998

Vax1 is a novel homeobox-containing gene expressed in the developing anterior ventral forebrain.

The vertebrate forebrain is formed at the rostral end of the neural plate under the regulation of local and specific signals emanating from both the endomesoderm and neuroectoderm. The development of the rostral and ventral forebrain in particular was difficult to study, mainly because no specific markers are available to date. Here, we report the identification of Vax1, a novel homeobox-containing gene identified in mouse, Xenopus and human. It is closely related to members of the Not and Emx gene families, all of which are required for the formation of structures where they are expressed. In mouse and Xenopus, Vax1 expression first occurs in the rostral neural plate, in the medial anterior neural ridge and adjacent ectoderm. Later, at midgestation in the mouse and tadpole stage in Xenopus, the expression remains confined in the derivatives of this territory which differentiate into rostromedial olfactory placode, optic nerve and disc, and anterior ventral forebrain. Together, these observations suggest that Vax1 could have an early evolutionary origin and could participate in the specification and formation of the rostral and ventral forebrain in vertebrates. Comparison of the limits of the expression territory of Vax1 with that of Dlx1, Pax6 and Emx1 indicates that the corticostriatal ridge is a complex structure with distinct identifiable genetic compartments. Besides, the study of Vax1 expression in Pax6-deficient homozygous brains indicates that its regulation is independent of Pax6, although the expression patterns of these two genes appear complementary in wild-type animals. Vax1 chromosomal location is mapped at the distal end of the mouse chromosome 19, linked with that of Emx2. These two genes may have arisen by tandem duplication. The Vax1 gene is thus an interesting new tool to study the rostral ventral forebrain patterning, morphogenesis and evolution as well as the terminal differentiation of the forebrain in mouse and Xenopus.

Amino Acid Sequence↗
PubMedDate not supplied

Transfer of chromic chloride to embryonic mice and changes in the embryonic mouse neuroepithelium.

Transfer of CrCl3 to embryonic mice and changes in the embryonic mouse neuroepithelium associated with Cr-induced neural tube defects were studied. A single intraperitoneal injection of 51CrCl3 was administered on the 8th day of gestation and animals were killed at various intervals for measurements of radioactivity in the maternal blood and embryos. Radioactivity per gram of fetal tissues increased during the observed period, while those of maternal blood decreased. Pregnant mice were injected intraperitoneally with a single dose of CrCl3 (non-radioactive) on the 8th day of gestation. Animals were killed at specified times after injection and embryos were removed and examined histologically. At 4, 8 and 12 h after injection many pyknotic cells were observed on the neural plate, especially at 8 h after injection. These data suggest that CrCl3 may affect embryos directly and cause neural tube defects and that pyknotic cells on the neural plate may be an early pathological finding in cases of developing exencephaly.

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