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At least 595 records · Page 33Linked to original sources

PubMed2000

Transcription mapping and expression analysis of candidate genes in the vicinity of the mouse Loop-tail mutation.

Loop-tail (Lp) is a semidominant mutation that maps to the distal portion of mouse Chromosome (Chr) 1 and is an established model for neural tube defects (NTDs). Homozygous embryos exhibit an open neural tube from the caudal midbrain to the tip of the tail that results from over-differentiation of the floor plate. To facilitate the positional cloning of the Lp gene, both cDNA selection and assignment of sequence-tagged-sites from the human transcript map have been used to identify genes within the Lp interval. Together with previous physical mapping, this has allowed the placement of 13 transcription units within an approximately 1-Mb region that spans the Lp genetic interval, and eight of these genes map to the nonrecombinant interval. This map includes genes that encode proteins involved in protein sorting and targeting (Tim23 and Copa), ion transport (Atp1a2, Atp1a4, and Girk3), transcription (Nhlh1), immune regulation (Cd48 and Fcer1alpha), cell adhesion (R88252), apoptosis (Pea15), and several of unknown function (H326, Kiaa0253, and Estm34). Expression analysis by Northern blotting indicated that a subset of these genes are expressed preferentially in the developing nervous system. Finally, this region of mouse Chr 1 represents a conserved linkage group with genes on human chromosome 1q21, a region that is frequently altered in human cancers and that harbors loci for several genetic conditions. Consequently, analysis of the Lp interval may provide important tools to understand how the corresponding region of human Chr 1 contributes to disease, in addition to defining a key gene product required for neurulation.

Animals↗

PubMed2003

Features of the developing brain.

INTRODUCTION: Fetal brain evaluation implies a perfect knowledge of the timing and characteristics of the developing nervous system during gestation. DISCUSSION: The first half of gestation corresponds to the neurulation, differentiation of primary cerebral vesicles, and neuronogenesis. The second half is characterized by the tremendous growth of the cerebral hemispheres and the settlement of gyral formation, while the ventricular system undergoes gradual narrowing. Gyral formation follows an invariable temporospatial schedule and is a good marker of fetal maturation. At the histological level, the fetal cortex displays transient developmental features, a superficial granular layer, and cells of Cajal-Retzius, which disappear at term. Neuroblasts formation has usually ceased by the 16th week of gestation, while neuronal migration continues until the extinction of the germinal layer. At this time, the remnant of the germinal layer constitutes, between the thalami and the caudate nucleus, an eminence of tightly packed cells, called the ganglionic eminence or germinal zone. They disappear by the age of 1 year.

Aging↗

PubMed2006

Congenital spinal dermal sinuses: poor awareness leads to delayed treatment.

OBJECTIVE: Congenital spinal dermal sinuses are relatively uncommon congenital abnormalities that result from abnormal neurulation. Lack of awareness about this problem, especially at the primary care level, results in these patients not being managed appropriately. This issue is highlighted in this case series of nine patients. MATERIALS AND METHODS: The nine patients--six males and three females--were treated over a 3-year period in two centres in the UK and India. The age varied from 212 months to 19 years. Clinical presentations included meningitis or neurological deficits. One was asymptomatic. MRI was done in all cases and showed the sinus tracts in all cases. In five cases, there were intramedullary dermoids and in the others the sinus tract ended either on the dura or blindly. All cases were treated surgically by excision of the sinus and tumour if any. In terms of the neurological status, one became normal, four improved and four remained the same. Of the four who remained the same, two had had normal neurological examination preoperatively. The mean duration from first assessment by a medical practitioner to correct diagnosis and referral to a neurosurgeon was 5 years (range 2 months to 18 years). Proper diagnosis and appropriate management was delayed in these cases because professionals were not aware of this condition. CONCLUSIONS: Primary care physicians should be made more aware about congenital spinal dermal sinuses. This will facilitate early diagnosis and referral to specialist services.

Adolescent↗

PubMed2000

Nasal encephaloceles.

Nasal encephaloceles can be divided into frontoethmoidal and basal encephaloceles. Both conditions are very rare, but frontoethmoidal encephaloceles show a relatively high incidence (1:5,000) in Southeast Asia. The pathogenesis of encephaloceles may be explained by a disturbance in separation of surface ectoderm (epithelial layer) and neurectoderm (nervous tissue) in the midline just after closure of the neural folds. It should be regarded as a 'late' neurulation defect taking place during the 4th gestational week. Apoptosis appears to be related to this separation process. Frontoethmoidal encephaloceles can be recognized as a facial mass covered with normal skin, while basal encephaloceles may cause nasal obstruction or symptoms related to herniation of basal structures. Diagnostic CT or MR imaging delineates the anatomy of the herniated mass. Therapy for frontoethmoidal encephaloceles consists in excision of the cele, watertight closure of the dural defect and reconstruction of the skull defect. Basal encephaloceles may harbour vital herniated structures which should be saved. Hydrocephalus should be dealt with first, followed by elective single-stage reconstructive surgery. The prognosis appears to be better for patients with frontoethmoidal encephaloceles than for patients with occipital or parietal encephaloceles, and it depends largely on the presence of additional congenital anomalies of the brain. The differential diagnosis of a nasal mass must include nasal glioma, dermoid cyst, and nasal polyp.

Child↗

PubMed2001

The curly tail mouse model of human neural tube defects demonstrates normal spinal cord differentiation at the level of the meningomyelocele: implications for fetal surgery.

The paralysis associated with lumbosacral meningomyelocele has been attributed both to myelodysplasia and to degeneration of the exposed neural tissue. Surgically created dysraphism shows that exposure of an intact spinal cord in a genetically normal animal results in degeneration of the normal nervous tissue and subsequent paralysis. Our objective was to study neuronal differentiation in the curly tail mouse mutant model, which develops lumbosacral meningomyelocele naturally and is a phenocopy of nonsyndromic human neural tube defects. Prenatal repair of meningomyelocele assumes that the normal neuronal differentiation program occurs despite failure of neurulation. Here we demonstrate that this most suitable animal model has normal differentiation of neuronal structures at the level of the meningomyelocele. TuJ1, an antibody to neuronal specific class III beta-tubulin, an early marker of neuronal differentiation, was used to stain paraffin-embedded sections of curly tail mouse embryo meningomyelocele. Embryos were examined at embryonic day 13.5 (E13.5). The inbred mouse strain, C57BL6/J, which is genetically similar to the curly tail mouse, was used as a control in these studies. We show that early neuronal differentiation appears intact within the meningomyelocele. TuJ stains structures within the open neural tube. Motor neurons are present in the ventral horn and ventral roots. Dorsal root ganglia are present and of similar size to controls. The staining pattern is similar to that seen in the C57BL/6J control mouse, although dorsal structures are laterally displaced in the curly tail meningomyelocele. Based on this model, fetal surgery to repair human meningomyelocele may preserve neurological function in those cases where there is not an inherent genetic defect of the neural tissue.

Animals↗

PubMed1997

Embryogenesis. Why do we need a new explanation for the emergence of spina bifida with lipoma?

Spina bifida with lipoma is a human malformation that most often affects the lumbosacral area. It is a complex morphological type. Its origin is controversial, and none of the previous hypotheses can be retained in view of the most recent advances in experimental embryogenesis. Contrary to earlier opinions, adipocytes cannot arise from meninges, vessels or glial cells and spina bifida cannot be explained by incarceration of mesodermal tissues during primary neurulation or developmental defect at the level of the tail bud. Spina bifida with lipoma, which actually involves all the derivatives of the so-called dorsal mesoderm, must therefore result from abnormal development of this mesoderm, which is induced by the dorsal neural tube. The location of the primary defect (dorsal mesoderm or neural tube) remains to be established.

Embryonic Induction↗

PubMed2006

Effect of maternal exposure to homocystine on sodium valproate-induced neural tube defects in the mouse embryos.

BACKGROUND: Neural tube defects (NTD) are mainly of multifactorial origin. Maternal treatment with valproic acid (VPA) during pregnancy induces NTD in susceptible fetuses. Elevated levels of homocysteine are observed in pregnancies with NTD. The mechanism by which homocysteine might cause NTD is unknown. AIM OF THE STUDY: The aim of this study was to determine if homocystine would augment VPA-induced exencephaly in an experimental model. METHODS: Groups of mice were injected (IP) on gestational day 8 (GD) with a single dose of 75 mg/kg of L: -Homocystine (HC) or a proportionate volume of saline, followed by a single dose of 600 mg/kg of VPA or an equal volume of saline. In a second experiment, mice were treated with a daily dose of 75 mg/kg of HC or an equal volume of saline (IP) from GD 5 and continued through GD 10. These animals had a single exposure to 600 mg/kg of VPA or saline (IP) on GD 8. All animals were killed by cervical dislocation on GD 18. Plasma homocysteine, folate and vitamin B12 were determined on GD 8 and GD 10 from single and multiple dose groups of mice, respectively, from additional experiments. RESULTS: The VPA and HC+VPA induced significantly higher rates of embryonic resorption and intrauterine growth retardation (IUGR) than HC or saline alone. HC + VPA groups had significantly more numerous fetuses with severe IUGR than HC alone or VPA alone groups. Both single and multiple doses of HC augmented VPA-induced reduction in fetal body weight. Successive doses of HC did not augment the rate of IUGR more significantly than a single dose of HC. Incidence of exencephaly was significantly enhanced in the HC + VPA groups compared to that in the HC or VPA alone groups. HC alone was not teratogenic. Plasma homocysteine levels increased several fold both in HC and HC + VPA groups and the increase was not particularly more marked in multiple dose groups than in the single dose groups. VPA did not elevate homocysteine concentration. Both FA and vitamin B12 concentrations were reduced by VPA, HC and HC + VPA, but HC and VPA when combined did not produce an additive effect on vitamin levels. CONCLUSION: These data indicate that HC and VPA interact in neurulation stage embryos, affect fundamental processes of closure of the neural tube and lead to enhanced incidence of NTD.

Abnormalities, Drug-Induced↗

PubMed2004

CD34-immunoreactive balloon cells in cortical malformations.

Balloon cells are histopathological hallmarks of various cortical malformations, i.e., focal cortical dysplasia (Taylor's type, FCD IIb), hemimegalencephaly (HME) or cortical tubers (tuberous sclerosis, TSC). Whether this intriguing cell type results from similar pathogenetic pathways remains to be shown. Here, we analyzed the immunohistochemical distribution pattern of the CD34 epitope in surgical specimens from 34 patients with FCD IIb, compared to that of 6 patients with TSC and 3 patients with HME. In normal brain, CD34 occurs only transiently during neurulation, but cannot be detected in mature neuroectodermal cell progenies. In contrast, 58% of our patients showed CD34 immunoreactivity within a subpopulation of balloon cells. Interestingly, CD34-positive balloon cells were confined to the white matter, but never observed in neocortical layers. Furthermore, balloon cells expressing neurofilament protein were also restricted to white matter, whereas GFAP-positive balloon cells were observed either in white or gray matter location. Clinical characteristics did not significantly differ between patients with CD34-positive versus CD34-negative lesions. No significant correlation was found between CD34 expression and genetic alterations of the TSC1 gene, which is affected in many FCD and TSC patients and which plays a role in the regulation of cell size. Further studies are warranted to clarify the restricted expression of CD34 in balloon cells of the white matter.

Adolescent↗

PubMed2001

Aprosencephaly: histopathological features of the rudimentary forebrain and retina.

Aprosencephaly/atelencephaly is an extremely rare central nervous system defect of the human fetus, which has been attributed to an encephaloclastic process. We report here the histopathological features of the rudimentary forebrain and retina of a case of aprosencephaly in a male fetus that was examined at 20 weeks of gestation, in which there was no evidence of destruction. The prosencephalon was excessively small and replaced by a solid, cylindrical mass without a hemispheric cleavage or a ventricle. Histologically, the rudimentary forebrain tissue consisted of primitive cells that had accumulated in the anterior portion, and of differentiated neurons and glia that were distributed in a random-manner in the posterior portion. The most rostral portion of the tissue penetrated the sphenoidal bone through a single canal: an extracranial ectopic nest consisted of primitive cells that were located at the posterior portion of the face. There were no eyelid openings, eyeballs, or optic nerves, although a nest of dysplastic retinal rosettes and two nests of melanin-pigmented epithelium were identified. This case seems to represent a primary malformation, and the features imply that the failure occurs after neurulation and before the prosencephalic medium began its growth.

Abnormalities, Multiple↗

PubMed1999

The CD34 epitope is expressed in neoplastic and malformative lesions associated with chronic, focal epilepsies.

The etiology and pathogenesis of complex focal lesions associated with chronic, intractable epilepsy are largely unknown. Some data indicate that malformative changes of the central nervous system may precede the development of gangliogliomas and other epilepsy-associated neoplasms. In the present immunhistochemical study, we have examined epilepsy-associated lesions for CD34, a stem cell marker transiently expressed during early neurulation. Surprisingly, most tissue samples from patients with chronic epilepsy (n = 262) revealed neural cells immunoreactive for CD34. Prominent immunoreactivity was detected in gangliogliomas (74%), low-grade astrocytomas (62%) and oligodendrogliomas (59%). Only 52% of non-neoplastic, malformative pathologies, such as glio-neuronal hamartias or hamartomas showed solitary or small clusters of CD34-immunoreactive cells. None of the adult control tissues (n = 22), none of the specimens obtained from the developing human brain (n = 44) and none of those tumor samples from patients without epilepsy (n = 63) contained CD34-immunoreactive neural cells. However, a malignant teratoma with microscopic features of early neural differentiation displayed a focal CD34-immunoreactive staining pattern. The majority of CD34-immunoreactive cells co-localized with S-100 protein and a small subpopulation was also immunoreactive for neuronal antigens. CD34 may, thus, represent a valuable marker for the diagnostic evaluation of neoplastic and/or malformative pathological changes in epilepsy patients. The CD34 immunoreactivity of these lesions indicates an origin from dysplastic or atypically differentiated neural precursors. Further studies may elucidate the functional significance of CD34 expression during the pathogenesis of epilepsy-related focal lesions as well as during neurogenesis.

Adolescent↗

PubMed2002

macho-1-Related genes in Ciona embryos.

In ascidians, maternal factor(s) localized in the myoplasm of the egg are essential for specification and subsequent differentiation of larval muscle cells. The macho-1 gene of Halocynthia roretzi encodes a zinc-finger protein: the gene is only expressed maternally, the resultant maternal mRNA is localized to the myoplasm, and the gene function is essential for muscle cell differentiation. Here we have characterized macho-1 homologues, Ci-macho1 of Ciona intestinalis and Cs-macho1 of Ciona savignyi. Interestingly, we found that the Ciona macho-1 genes are expressed both maternally and zygotically: their maternal transcript is localized to the myoplasm while their zygotic expression is seen after neurulation in cells of the central nervous system. Functional suppression of Cs-macho1 with morpholino antisense oligonucleotide resulted in inhibition of the initiation of zygotic expression of a muscle-specific actin gene. We propose a possible evolutionary scenario in which an ancestral Zic-related gene gave rise to both the macho-1-like muscle determinant gene as well as neuronal Zic genes.

Amino Acid Sequence↗

PubMed2003

Cloning and expression patterns of dystroglycan during the early development of Xenopus laevis.

Dystroglycan is a cell surface receptor involved in the pathogenesis of muscular dystrophy, and plays a critical role in the assembly and homeostasis of basement membranes. Since data about the amphibian homologue are limited, we have cloned the full-length dystroglycan cDNAs from the frog Xenopus laevis. Using in situ hybridization, we show that mRNA expression is dynamic, particularly in the notochord at the end of gastrulation and during neurulation, suggesting that the protein might play unexplored roles in the specification and/or formation of this tissue. Subsequently, the transcripts are detected in the otic vesicle, the developing brain, and in mesenchymal cells of the visceral arches, as well as in pharyngeal endoderm, the pronephros, pronephric ducts, proctodaeum and the somites.

Amino Acid Sequence↗

PubMed2004

Isolation and developmental expression of Xenopus FoxJ1 and FoxK1.

xFoxJ1 and xFoxK1, two novel members of the fork head/winged helix family of transcription factors in Xenopus, have been identified by sequence homology to their mammalian orthologues. We here report the complete amino acid sequences of xFoxJ1, its pseudo-allelic version xFoxJ1', and of xFoxK1, the latter also comprising a fork-head-associated (FHA) domain. We have further analysed the temporal and spatial expression of both genes. xFoxJ1 transcripts were detected during gastrulation in the dorsal blastopore lip and in the animal half. A predominant feature of xFoxJ1 expression until the tailbud stage is its spotty pattern within the epidermis. xFoxK1 is maternally expressed and localized within the animal half during early cleavage stages. Zygotic transcription starts during neurulation and is initially restricted to neuroectoderm. As development proceeds, xFoxK1 is expressed in ectoderm- and mesoderm-derived tissues, like the branchial arches, brain, eye, otic vesicle, pronephros, somites and abdominal muscle precursors.

Amino Acid Sequence↗

PubMed2000

Expression and subcellular localization of X-ATM during early Xenopus development.

ATM, the gene mutated in ataxia telangiectasia, is a protein essential for handling DNA strand breaks. We recently isolated the Xenopus homologue of ATM, X-ATM and we report here the detailed expression pattern of the protein and the mRNA during early Xenopus development. During the cleavage stages, ATM protein was concentrated in and around the nuclei of all cells with low levels of expression also detected in the cytoplasm. Following neurulation, increased protein levels were detected in the nuclei of developing somites and in the central nervous system. Areas of high protein expression correlated with areas of increased mRNA expression which was detected in the nuclei of somites and the developing lens.

Animals↗

PubMed2000

Xnkx-2.1: a homeobox gene expressed during early forebrain, lung and thyroid development in Xenopus laevis.

Nkx-2.1 is a member of the vertebrate Nkx family of homeobox genes; it was originally identified as a tissue-specific regulator of thyroglobulin and thyroperoxidase gene transcription. Here we report on the embryonic expression of Xnkx-2.1, which is expressed in the presumptive forebrain from early neurulation onwards. In tadpole stage embryos Xnkx-2.1 transcripts are primarily detected in ventral forebrain, lung buds and thyroid anlage. Therefore, Xnkx-2.1 may be part of the genetic network that controls the early development of these organs.

Amino Acid Sequence↗

PubMed1998

Regulation of SPARC expression during early Xenopus development: evolutionary divergence and conservation of DNA regulatory elements between amphibians and mammals.

SPARC (Secreted Protein, Acidic, Rich in Cysteine/osteonectin/BM-40) is a highly conserved metal-binding extracellular matrix (ECM) glycoprotein which is first expressed by Xenopus embryos during late gastrulation/early neurulation (stage 12/13), by presumptive notochord and somitic cells. When animal cap explants of stage 9 embryos were cultured in vitro, SPARC expression was not detected until sibling embryos reached late neurula stage (stage 19). Addition of activin, a potent dorsal mesoderm inducer, to animal caps resulted in SPARC being expressed by the time sibling embryos reached stage 16. While basic fibroblast growth factor (bFGF), a ventral mesoderm inducer, had modest effects on SPARC mRNA expression, the combination of both activin and bFGF was synergistic. The appearance, however, of SPARC transcripts 11 h after the addition of activin and bFGF, indicates that unknown intermediates were likely to be involved in activating SPARC expression. In order to identify the potential intermediate regulatory factors which may activate and control SPARC expression, we examined the genomic organization of the 5' end of the Xenopus SPARC gene. No significant homology to the equivalent region that is highly conserved in the mouse, bovine and human SPARC genes was observed. Thus, while mammalian SPARC promoters lack TATA or CAAT boxes, the Xenopus gene contains a consensus TATA box. Moreover, promoter-proximal GGA-box repeats necessary for high level expression of mammalian SPARC are absent in Xenopus. When reporter constructs containing the 5' flanking region of the Xenopus gene were microinjected into two-cell embryos, 868 bp of 5' flanking DNA was sufficient to mimic the temporal and tissue-specific pattern of SPARC expression observed in whole embryos. While a bovine SPARC promoter reporter construct containing 740 bp of the 5' flanking DNA was expressed at a significant level in Xenopus embryos, significant differences in the cell-type expression of the reporter genes were obtained between the bovine and Xenopus constructs. The data indicate that zygotic activation of SPARC mRNA is mediated by regulatory factors acting downstream of major mesoderm induction events. The high DNA sequence conservation at the 5' end of mammalian SPARC genes is not conserved in Xenopus. These differences led to differences in their ability to direct tissue-specific gene expression in early Xenopus embryos.

Activins↗

PubMed1998

An amphioxus snail gene: expression in paraxial mesoderm and neural plate suggests a conserved role in patterning the chordate embryo.

Homologs of the Drosophila snail gene have been characterized in several vertebrates. In addition to being expressed in mesoderm during gastrulation, vertebrate snail genes are also expressed in presumptive neural crest and/or its derivatives. Given that neural crest is unique to vertebrates and is considered to be of fundamental importance in their evolution, we have cloned and characterized the expression of a snail gene from amphioxus, a cephalochordate widely accepted as the sister group of the vertebrates. We show that, at the amino acid sequence level, the amphioxus snail gene is a clear phylogenetic outgroup to all the characterized vertebrate snail genes. During embryogenesis snail expression initially becomes restricted to the paraxial or presomitic mesoderm of amphioxus. Later, snail is expressed at high levels in the lateral neural plate, where it persists during neurulation. Our results indicate that an ancestral function of snail genes in the lineage leading to vertebrates is to define the paraxial mesoderm. Furthermore, our results indicate that a cell population homologous to the vertebrate neural crest may be present in amphioxus, thus providing an important link in the evolution of this key vertebrate tissue.

Amino Acid Sequence↗

PubMed2000

Neuroectodermal and endodermal expression of the ascidian Cdx gene is separated by metamorphosis.

Ascidians are a group of invertebrate chordates that exhibit a biphasic life history, with chordate-specific structures developing during embryogenesis (dorsal neural tube and notochord) and metamorphosis (pharyngeal gill slits and endostyle). Here we characterize the expression of a caudal/Cdx gene homologue, Hec-Cdx, from the ascidian Herdmania curvata. Vertebrate Cdx genes are expressed at gastrulation and in the posterior of the developing neural tube and endoderm. Hec-Cdx expression is initiated at the earliest stages of gastrulation, with peaks in RNA abundance occurring first during neurulation and tailbud extension and then in 3- to 5-day-old juveniles. Hec-Cdx is expressed in a pair of cells in the anterior lip of the blastopore in the late gastrula which form the most posterior portion of the neural plate. During tailbud formation expression is maintained in and solely restricted to these cells. During metamorphosis expression is localized to the intestine of the juvenile. These data, along with data for the H. curvata Otx gene, suggest that the evolution of the novel ascidian biphasic body plan was not accompanied by a deployment of these genes into new pathways but by a temporal separation of tissue-specific expression.

Amino Acid Sequence↗