Mouse-chick neural chimeras

Embryonic chimera production was used to study the developmental processes of the mouse nervous system. The difficulty of performing in situ transplantation experiments of neural primordium of mouse embryo was overcome by isotopic and isochronic grafting of mouse neural tube fragments into chick embryo. Mouse neural tube cells differentiated perfectly in ovo and neural crest cells associated with the grafted neural tube were able to migrate and reach the normal arrest sites of host neural crests. Cranial neural crest cells penetrated into chick facial areas and entered into the development of dental bud structures, participating in vibrissa formation. Depending on graft level, in ovo implanted mouse neural crest cells formed different components of the peripheral nervous system. At trunk level, they located in spinal ganglia and orthosympathetic chains and gave rise to Schwann cells lining the nerves. When implanted into the lumbosacral region, they penetrated into the enteric nervous system. At the precise 18-24 somite level, they colonized host adrenal gland. Mouse neural tube was involved in the mechanisms required to maintain myogenesis in host somites. Furthermore in ovo grafts of mouse cells from genetically modified embryos, in which many mutations induce early death, are particularly useful to investigate cellular events involved in the development of the nervous system and to identify molecular events of embryogenesis.     

Assessing Primary Neurogenesis in Xenopus Embryos Using Immunostaining

Primary neurogenesis is a dynamic and complex process during embryonic development that sets up the initial layout of the central nervous system. During this process, a portion of neural stem cells undergo differentiation and give rise to the first populations of differentiated primary neurons within the nascent central nervous system. Several vertebrate model organisms have been used to explore the mechanisms of neural cell fate specification, patterning, and differentiation. Among these is the African clawed frog, Xenopus, which provides a powerful system for investigating the molecular and cellular mechanisms responsible for primary neurogenesis due to its rapid and accessible development and ease of embryological and molecular manipulations. Here, we present a convenient and rapid method to observe the different populations of neuronal cells within Xenopus central nervous system. Using antibody staining and immunofluorescence on sections of Xenopus embryos, we are able to observe the locations of neural stem cells and differentiated primary neurons during primary neurogenesis.     

In vitro differentiation of transplantable neural precursors from human embryonic stem cells.

The remarkable developmental potential and replicative capacity of human embryonic stem (ES) cells promise an almost unlimited supply of specific cell types for transplantation therapies. Here we describe the in vitro differentiation, enrichment, and transplantation of neural precursor cells from human ES cells. Upon aggregation to embryoid bodies, differentiating ES cells formed large numbers of neural tube-like structures in the presence of fibroblast growth factor 2 (FGF-2). Neural precursors within these formations were isolated by selective enzymatic digestion and further purified on the basis of differential adhesion. Following withdrawal of FGF-2, they differentiated into neurons, astrocytes, and oligodendrocytes. After transplantation into the neonatal mouse brain, human ES cell-derived neural precursors were incorporated into a variety of brain regions, where they differentiated into both neurons and astrocytes. No teratoma formation was observed in the transplant recipients. These results depict human ES cells as a source of transplantable neural precursors for possible nervous system repair.     

Compatibility of cells of the nervous system with structured biodegradable chitosan-based hydrogel matrices

Hydrogel matrices for cell cultivation have been generated by two-photon laser polymerization of unsaturated chitosan derivatives and methacrylated hyaluronic acid. The adhesive and toxic properties of the matrices have been assessed, and the matrices have been shown to have a good compatibility with primary hippocampal cell cultures. The formation of morphologically normal neural networks by cells of the nervous system cultured on the surface of hydrogel matrices has been observed. The metabolic status of dissociated hippocampal cells cultured on the matrices was similar to that of the control cultures, as shown by the results of MTT reductase activity assay. Thus, matrices based on unsaturated polysaccharide derivatives crosslinked by laser irradiation showed good compatibility with differentiated cells of the nervous system and considerable potential for use in neurotransplantation.     

Stem cell factor is a chemoattractant and a survival factor for CNS stem cells

Migration of neural cells to their final positions is crucial for the correct formation of the central nervous system. Several extrinsic factors are known to be involved in the regulation of neural migration. We asked if stem cell factor (SCF), well known as a chemoattractant and survival factor in the hematopoietic lineage, could elicit similar responses in neural stem cells. For that purpose, a microchemotaxis assay was used to study the effect of SCF on migration of neural stem cells from the embryonic rat cortex. Our results show that SCF-induced chemotaxis and that specific antibodies to SCF or tyrosine kinase inhibitors abolished the migratory response. The SCF-receptor, Kit, was expressed in neural stem cells and in their differentiated progeny. We also show that SCF is a survival factor, but not a mitogen or a differentiation factor for neural stem cells. These data suggest a role for SCF in cell migration and survival in the developing cortex.     

A labile period in the determination of the anterior-posterior axis during early neural development in Xenopus.

The process by which the vertebrate central nervous system acquires its regional properties remains a central problem in developmental biology. It is generally argued that at early gastrula stages the dorsal mesoderm possesses precise anterior-posterior positional information, which is subsequently imparted to the overlying ectoderm. However, using regionally specific gene probes to monitor regional responses in Xenopus embryos, we find that anterior-posterior properties are not fixed until early neurula stages. During gastrulation the regional inducing capacities of the dorsal mesoderm as well as the regional responses of the presumptive neural ectoderm are activated along the entire anterior-posterior axis when these properties are assayed in recombinant and explant experiments, respectively. Restriction of regional inducing capacity in the mesoderm and responsiveness in the neural ectoderm occur only at neural plate stages.     

Multiple roles of mouse Numb in tuning developmental cell fates.

BACKGROUND: Notch signaling regulates multiple differentiation processes and cell fate decisions during both invertebrate and vertebrate development. Numb encodes an intracellular protein that was shown in Drosophila to antagonize Notch signaling at binary cell fate decisions of certain cell lineages. Although overexpression experiments suggested that Numb might also antagonize some Notch activity in vertebrates, the developmental processes in which Numb is involved remained elusive. RESULTS: We generated mice with a homozygous inactivation of Numb. These mice died before embryonic day E11.5, probably because of defects in angiogenic remodeling and placental dysfunction. Mutant embryos had an open anterior neural tube and impaired neuronal differentiation within the developing cranial central nervous system (CNS). In the developing spinal cord, the number of differentiated motoneurons was reduced. Within the peripheral nervous system (PNS), ganglia of cranial sensory neurons were formed. Trunk neural crest cells migrated and differentiated into sympathetic neurons. In contrast, a selective differentiation anomaly was observed in dorsal root ganglia, where neural crest--derived progenitor cells had migrated normally to form ganglionic structures, but failed to differentiate into sensory neurons. CONCLUSIONS: Mouse Numb is involved in multiple developmental processes and required for cell fate tuning in a variety of lineages. In the nervous system, Numb is required for the generation of a large subset of neuronal lineages. The restricted requirement of Numb during neural development in the mouse suggests that in some neuronal lineages, Notch signaling may be regulated independently of Numb.     

Novel roles for collagens in wiring the vertebrate nervous system

Wiring the vertebrate nervous system is a multi-step process that relies heavily upon the role of transmembrane and extracellular adhesion molecules. Despite the extensive attention focused on such molecules, collagens, a large family of structural adhesion molecules expressed in the vertebrate nervous system, have been largely overlooked for roles in neural circuit formation. Recently, however, several studies have unexpectedly identified novel roles of collagens and collagen-like molecules in the developing vertebrate nervous system. Here, contributions of these collagens and collagen-like molecules in neural circuit formation are reviewed.     

The expression and function of the achaete-scute genes in Tribolium castaneum reveals conservation and variation in neural pattern formation and cell fate specification

The study of achaete-scute (ac/sc) genes has recently become a paradigm to understand the evolution and development of the arthropod nervous system. We describe the identification and characterization of the ac/sc genes in the coleopteran insect species Tribolium castaneum. We have identified two Tribolium ac/sc genes - achaete-scute homolog (Tc-ASH) a proneural gene and asense (Tc-ase) a neural precursor gene that reside in a gene complex. Focusing on the embryonic central nervous system we find that Tc-ASH is expressed in all neural precursors and the proneural clusters from which they segregate. Through RNAi and misexpression studies we show that Tc-ASH is necessary for neural precursor formation in Tribolium and sufficient for neural precursor formation in Drosophila. Comparison of the function of the Drosophila and Tribolium proneural ac/sc genes suggests that in the Drosophila lineage these genes have maintained their ancestral function in neural precursor formation and have acquired a new role in the fate specification of individual neural precursors. Furthermore, we find that Tc-ase is expressed in all neural precursors suggesting an important and conserved role for asense genes in insect nervous system development. Our analysis of the Tribolium ac/sc genes indicates significant plasticity in gene number, expression and function, and implicates these modifications in the evolution of arthropod neural development.     

Amigo Adhesion Protein Regulates Development of Neural Circuits in Zebrafish Brain

The Amigo protein family consists of three transmembrane proteins characterized by six leucine-rich repeat domains and one immunoglobulin-like domain in their extracellular moieties. Previous in vitro studies have suggested a role as homophilic adhesion molecules in brain neurons, but the in vivo functions remain unknown. Here we have cloned all three zebrafish amigos and show that amigo1 is the predominant family member expressed during nervous system development in zebrafish. Knockdown of amigo1 expression using morpholino oligonucleotides impairs the formation of fasciculated tracts in early fiber scaffolds of brain. A similar defect in fiber tract development is caused by mRNA-mediated expression of the Amigo1 ectodomain that inhibits adhesion mediated by the full-length protein. Analysis of differentiated neural circuits reveals defects in the catecholaminergic system. At the behavioral level, the disturbed formation of neural circuitry is reflected in enhanced locomotor activity and in the inability of the larvae to perform normal escape responses. We suggest that Amigo1 is essential for the development of neural circuits of zebrafish, where its mechanism involves homophilic interactions within the developing fiber tracts and regulation of the Kv2.1 potassium channel to form functional neural circuitry that controls locomotion.     

Neurobiorheology. A new branch of biorheology. Historical background and current ideas.

The application of principles of biorheology, hemorheology and perihemorheology on problems of the nervous system in health and disease was suggested by Alfred L. Copley (1982, 1987). Late in 1988 Copley and Sourander considered neurobiorheology to be an appropriate term for a new branch of biorheology bridging the gap between biorheology and neurobiology. Neurobiorheology can be defined as a research field concerned with deformation behaviour of matter including flow and transportation in context with the structure and function of the nervous system at macroscopic, cellular, subcellular and molecular levels. It may be considered a basic life science with important clinical applications. Its "raison d'être" should be to apply various ways of thinking, calculations and techniques used in biorheology to treat and if possible to solve neurobiological problems. Many regionally different chemical, structural and functional properties characterize the developing and adult nervous system and those parts of the circulatory system ("vessel-blood organ") which penetrate the nervous system at all levels. Considering the close metabolic and functional relations between neurons and surrounding non-neuronal ectodermal cells, neuroglial and Schwann cells deriving from common precursor cells in the wall of the neural tube and neural crest respectively, the term neuroectodermal organ appears suitable. The almost parallel ontogenetic evolution of vessel-blood organ and neuroectodermal organ and their interaction during the entire individual life cycle constitutes a challenging stimulus for integrated research. The main purpose of this review is to give some examples of importance concerning still insufficiently elucidated neurobiological problems suitable for biorheological approaches. Particular attention will be paid to the microenvironment at central and peripheral levels of the neuroectodermal organ.     

Planar and vertical signals in the induction and patterning of the Xenopus nervous system.

The cellular mechanisms responsible for the formation of the Xenopus nervous system have been examined in total exogastrula embryos in which the axial mesoderm appears to remain segregated from prospective neural ectoderm and in recombinates of ectoderm and mesoderm. Posterior neural tissue displaying anteroposterior pattern develops in exogastrula ectoderm. This effect may be mediated by planar signals that occur in the absence of underlying mesoderm. The formation of a posterior neural tube may depend on the notoplate, a midline ectodermal cell group which extends along the anteroposterior axis. The induction of neural structures characteristic of the forebrain and of cell types normally found in the ventral region of the posterior neural tube requires additional vertical signals from underlying axial mesoderm. Thus, the formation of the embryonic Xenopus nervous system appears to involve the cooperation of distinct planar and vertical signals derived from midline cell groups.