Inhibition of neural crest migration in Xenopus using antisense slug RNA. (41/2353)

Based primarily on studies in the chick, it has been assumed that the zinc finger transcription factor Slug is required for neural crest migration. In the mouse, however, Slug is not expressed in the premigratory neural crest, which forms normally in Slug -/- animals. To study the role of Slug in Xenopus laevis, we used the injection of XSlug antisense RNA and tissue transplantation. Injection of Slug antisense RNA did not suppress the early expression of the related gene XSnail, but led to reduced expression of both XSlug and XSnail in later stage embryos, whereas the expression of another neural crest marker, XTwist, was not affected. Down-regulation of XSlug and XSnail was associated with the inhibition of neural crest cell migration and the reduction or loss of many neural crest derivatives. In particular, the formation of rostral cartilages was often highly aberrant, whereas the posterior cartilages were less frequently affected. The effects of Slug antisense RNA on neural crest migration and cartilage formation were rescued by the injection of either XSlug or XSnail mRNA. These studies indicate that XSlug is required for neural crest migration, that XSlug and XSnail may be functionally redundant, and that both genes are required to maintain each other's expression in the neural crest development of xenopus laevis.  (+info)

Zebrafish narrowminded suggests a genetic link between formation of neural crest and primary sensory neurons. (42/2353)

In the developing vertebrate nervous system, both neural crest and sensory neurons form at the boundary between non-neural ectoderm and the neural plate. From an in situ hybridization based expression analysis screen, we have identified a novel zebrafish mutation, narrowminded (nrd), which reduces the number of early neural crest cells and eliminates Rohon-Beard (RB) sensory neurons. Mosaic analysis has shown that the mutation acts cell autonomously suggesting that nrd is involved in either the reception or interpretation of signals at the lateral neural plate boundary. Characterization of the mutant phenotype indicates that nrd is required for a primary wave of neural crest cell formation during which progenitors generate both RB sensory neurons and neural crest cells. Moreover, the early deficit in neural crest cells in nrd homozygotes is compensated later in development. Thus, we propose that a later wave can compensate for the loss of early neural crest cells but, interestingly, not the RB sensory neurons. We discuss the implications of these findings for the possibility that RB sensory neurons and neural crest cells share a common evolutionary origin.  (+info)

Regeneration of isthmic tissue is the result of a specific and direct interaction between rhombomere 1 and midbrain. (43/2353)

The midbrain-hindbrain boundary, or isthmus, is the source of signals that are responsible for regional specification of both the midbrain and anterior hindbrain. Fibroblast growth factor 8 (Fgf8) is expressed specifically at the isthmus and there is now good evidence that it forms at least part of the patterning signal. In this study, we use Fgf8 as a marker for isthmic cells to examine how interactions between midbrain and hindbrain can regenerate isthmic tissue and, thereby, gain insight into the normal formation and/or maintenance of the isthmus. We show that Fgf8-expressing tissue with properties of the isthmic organiser is generated when midbrain and rhombomere 1 tissue are juxtaposed but not when midbrain contacts any other rhombomere. The use of chick/quail chimeras shows that the isthmic tissue is largely derived from rhombomere 1. In a few cases a small proportion of the Fgf8-positive cells were of midbrain origin but this appears to be the result of a local respecification to a hindbrain phenotype, a process mimicked by ectopic FGF8. Studies in vitro show that the induction of Fgf8 is the result of a direct planar interaction between the two tissues and involves a diffusible signal.  (+info)

Ecotropic viral integration site-1 is activated during, and is sufficient for, neuroectodermal P19 cell differentiation. (44/2353)

Expression of the ecotropic viral integration site-1 (Evi1) proto-oncogene during murine embryonal development is observed by in situ hybridization in primary head folds and neural crest-derived cells associated with the peripheral nervous system and embryonic mesoderm. To elucidate whether expression of Evi1 is involved in early neuroectodermal or mesodermal differentiation, we used murine embryonal carcinoma P19 cells as a model for the study of early embryonic differentiation. After retinoic acid (RA) treatment with aggregation, expression of Evi1 was detected during neural differentiation in P19 cells. However, Evi1 was not expressed in P19 cells during mesodermal differentiation after DMSO treatment with aggregation. Enforced expression of Evi1 in P19 cells induced neuron-specific microtubule-associated protein-2 microtubule-associated protein-2 and TrkA expression in the absence of RA under monolayer culture. After incubation with RA with aggregation, the Evi1 clones expressed microtubule-associated protein-2 continuously but did not express glial fibrillary acidic protein as an astrocyte marker protein until 12 days of culture. Thus, the overexpression of Evi1 leads to neural differentiation of P19 cells and blocks further differentiation into astrocytes by RA treatment, suggesting that Evi1 might be an important transcription factor for regulation of early neuroectodermal differentiation.  (+info)

Ventrally emigrating neural tube cells contribute to the formation of Meckel's and quadrate cartilage. (45/2353)

A population of multipotential neuroepithelial cells originating in the ventral portion of the hindbrain neural tube has been shown recently to emigrate at the site of attachment of the trigeminal nerve. These ventrally emigrating neural tube cells populate the mesenchyme of the first pharyngeal (branchial) arch. Because the Meckel's and the quadrate cartilage develop from this mesenchyme, we sought to determine whether these ventrally emigrating neural tube cells contributed to their development. The ventral neural tube cells were tagged with a replication-deficient retroviral vector containing the LacZ gene. This method permanently labels the descendents of the neural tube cells; thus, they can be subsequently tracked during development. The viral concentrate was microinjected into the lumen of the rostral hindbrain of chick embryos, after the emigration of neural crest is finished, on embryonic day 2 (stage 14). In control embryos, the virus was placed on top of the neural tube. Embryos were killed on days 3, 4, and 7 and processed for the detection of LacZ-positive cells. By day 7, the Meckel's and the quadrate cartilage can be easily recognized. LacZ-positive cells were seen in both cartilages. They were located in perichondrium and in the cartilage. Immunostaining with the neural crest cell marker HNK-1 indicated that the LacZ-positive cells were HNK-1 negative. The HNK-1-positive neural crest-derived cells were located in the cartilage but not in the perichondrium. These results indicate that the chondrocytes in the Meckel's and the quadrate cartilage differentiate from two sources of cells; the ventrally emigrating neural tube cells and the neural crest. The developmental significance of differentiation of cartilage from the ventral neural tube cells and of the heterogeneous origin of chondrocytes in morphogenesis remains to be established. Dev Dyn 1999;216:37-44.  (+info)

Functional association of retinoic acid and hedgehog signaling in Xenopus primary neurogenesis. (46/2353)

Previous work has shown that the posteriorising agent retinoic acid can accelerate anterior neuronal differentiation in Xenopus laevis embryos (Papalopulu, N. and Kintner, C. (1996) Development 122, 3409-3418). To elucidate the role of retinoic acid in the primary neurogenesis cascade, we investigated whether retinoic acid treatment of whole embryos could change the spatial expression of a set of genes known to be involved in neurogenesis. We show that retinoic acid expands the N-tubulin, X-ngnr-1, X-MyT1, X-&Dgr;-1 and Gli3 domains and inhibits the expression of Zic2 and sonic hedgehog in the neural ectoderm, whereas a retinoid antagonist produces opposite changes. In contrast, sonic and banded hedgehog overexpression reduced the N-tubulin stripes, enlarged the neural plate at the expense of the neural crest, downregulated Gli3 and upregulated Zic2. Thus, retinoic acid and hedgehog signaling have opposite effects on the prepattern genes Gli3 and Zic2 and on other genes acting downstream in the neurogenesis cascade. In addition, retinoic acid cannot rescue the inhibitory effect of Notch(ICD), Zic2 or sonic hedgehog on primary neurogenesis. Our results suggest that retinoic acid acts very early, upstream of sonic hedgehog, and we propose a model for regulation of differentiation and proliferation in the neural plate, showing that retinoic acid might be activating primary neurogenesis by repressing sonic hedgehog expression.  (+info)

Characterization of the early development of specific hypaxial muscles from the ventrolateral myotome. (47/2353)

We have previously found that the myotome is formed by a first wave of pioneer cells generated along the medial epithelial somite and a second wave emanating from the dorsomedial lip (DML), rostral and caudal edges of the dermomyotome (Kahane, N., Cinnamon, Y. and Kalcheim, C. (1998a) Mech. Dev. 74, 59-73; Kahane, N., Cinnamon, Y. and Kalcheim, C. (1998b) Development 125, 4259-4271). In this study, we have addressed the development and precise fate of the ventrolateral lip (VLL) in non-limb regions of the axis. To this end, fluorescent vital dyes were iontophoretically injected in the center of the VLL and the translocation of labeled cells was followed by confocal microscopy. VLL-derived cells colonized the ventrolateral portion of the myotome. This occurred following an early longitudinal cell translocation along the medial boundary until reaching the rostral or caudal dermomyotome lips from which fibers emerged into the myotome. Thus, the behavior of VLL cells parallels that of their DML counterparts which colonize the opposite, dorsomedial portion of the myotome. To precisely understand the way the myotome expands, we addressed the early generation of hypaxial intercostal muscles. We found that intercostal muscles were formed by VLL-derived fibers that intermingled with fibers emerging from the ventrolateral aspect of both rostral and caudal edges of the dermomyotome. Notably, hypaxial intercostal muscles also contained pioneer myofibers (first wave) showing for the first time that lateral myotome-derived muscles contain a fundamental component of fibers generated in the medial domain of the somite. In addition, we show that during myotome growth and evolution into muscle, second-wave myofibers progressively intercalate between the pioneer fibers, suggesting a constant mode of myotomal expansion in its dorsomedial to ventrolateral extent. This further suggests that specific hypaxial muscles develop following a consistent ventral expansion of a 'compound myotome' into the somatopleure.  (+info)

In vivo transplantation of mammalian neural crest cells into chick hosts reveals a new autonomic sublineage restriction. (48/2353)

The study of mammalian neural crest development has been limited by the lack of an accessible system for in vivo transplantation of these cells. We have developed a novel transplantation system to study lineage restriction in the rodent neural crest. Migratory rat neural crest cells (NCCs), transplanted into chicken embryos, can differentiate into sensory, sympathetic, and parasympathetic neurons, as shown by the expression of neuronal subtype-specific and pan-neuronal markers, as well as into Schwann cells and satellite glia. In contrast, an immunopurified population of enteric neural precursors (ENPs) from the fetal gut can also generate neurons in all of these ganglia, but only expresses appropriate neuronal subtype markers in Remak's and associated pelvic parasympathetic ganglia. ENPs also appear restricted in the kinds of glia they can generate in comparison to NCCs. Thus ENPs have parasympathetic and presumably enteric capacities, but not sympathetic or sensory capacities. These results identify a new autonomic lineage restriction in the neural crest, and suggest that this restriction preceeds the choice between neuronal and glial fates.  (+info)