ISSN:0022-3034    

DOI:10.1002/neu.480241002

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractIn amphibians and other vertebrates, neural development is induced in the ectoderm by signals coming from the dorsal mesoderm during gastrulation. Classical embryological results indicated that these signals follow a “vertical” path, from the involuted dorsal mesoderm to the overlying ectoderm. Recent work with the frogXenopus laevis, however, has revealed the existence of “planar” neural‐inducing signals, which pass within the continuous sheet or plane of tissue formed by the dorsal mesoderm and presumptive neurectoderm. Much of this work has made use of Keller explants, in which dorsal mesoderm and ectoderm are cultured in a planar configuration with contact along only a single edge, and vertical contact is prevented. Planar signals can induce the full anteroposterior (A‐P) extent of neural pattern, as evidenced in Keller explants by the expression of genes that mark specific positions along the A‐P axis. In this review, classical and modern molecular work on vertical and planar inductionwill be discussed. This will be followed by a discussion of various models for vertical induction and planar induction. It has been proposed that the A‐P pattern in the nervous system is derived from a parallel pattern of inducers in the dorsal mesoderm which is “imprinted” vertically onto the overlying ectoderm. Since it is now known that planar signals can also induce A‐P neural pattern, this kind of model must be reassessed. The study of planar induction of A‐P pattern inXenopusembryos provides a simple, manipulable, two‐dimensional system in which to investigate pattern formation. ©

ISSN:0022-3034    

DOI:10.1002/neu.480241003

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractIn this review I summarize recent findings on the contributions of different cell groups to the formation of the basic plan of the nervous system of vertebrate embryos. Midline cells of the mesoderm—the organizer, notochord, and prechordal plate—and midline cells of the neural ectoderm—the notoplate and floor plate—appear to have a fundamental role in the induction and patterning of the neural plate. Vertical signals acting across tissue layers and planar signals acting through the neural epithelium have distinct roles and cooperate in induction and pattern formation. Whereas the prechordal plate and notochord have distinct vertical signaling properties, the initial anteroposterior (A‐P) pattern of the neural plate may be induced by planar signals originating from the organizer region. Planar signals from the notoplate may also contribute to the mediolateral (M‐L) patterning of the neural plate. These and other findings suggest a general view of neural induction and axial patterning. © 1993 John Wil

ISSN:0022-3034    

DOI:10.1002/neu.480241004

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe neuroectoderm of insects contains an initially indifferent population of cells which during later development will give rise to the progenitor cells of the neural and epidermal lineages. Experimental evidence indicates that cellular interactions determine which cells will adopt each one of these fates. Transplantation experiments suggest that a signal with neuralising character is required to stabilize the primary neural fate in 25% of all the neuroectodermal cells, which will develop as neuroblasts, and that an epidermalising signal contributes to suppress the neural fate in the remaining 75% of the cells, allowing in this way their development as epidermal progenitor cells. The invoked cell interactions are assumed to be mediated by the products of several genes forming a complex, not yet well understood network of interrelationships. Elements of this network are the proteins encoded byDeltaandNotch, which appear to convey the regulatory signals between the cells; the proteins encoded by theachaete‐scutegene complex, which regulate neural development; and the proteins encoded by theEnhancer of splitgene complex, which give neuroectodermal cells access to epidermal development. © 1993 John Wiley&Sons, I

ISSN:0022-3034    

DOI:10.1002/neu.480241005

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractTheHoxfamily of homeobox‐containing genes are intimately associated with the processes of axial patterning in vertebrate embryos. This family of transcription factors is widely conserved in evolution and by analogy with theirDrosophilacounterparts, theHOM‐Chomeotic genes, may play a role in establishing regional identity in a number of embryonic systems, including the CNS. The patterns of expression of these genes are linked with the generation of rhombomeres and neural crest in the developing hindbrain, and suggest that they provide a molecular system for generating a combinatorial patterning mechanism. Analysis of mouseHoxmutants generated by homologous recombination have clearly demonstrated that the genes have important roles in normal regionalisation of the hindbrain and branchial arches, and this has lead to interest in how their early patterns are established in the nervous system. TheHoxgenes and their relation to hindbrain segmentation therefore provide a means of examining the cascade of events which regulates pattern formation in early neural development. © 1993 John Wiley&Sons,

ISSN:0022-3034    

DOI:10.1002/neu.480241006

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0022-3034    

DOI:10.1002/neu.480241007

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWe have analyzed the expression of four mouse homeobox genes related to twoDrosophilagenes expressed in the developing head of the fly. Two of these genes, Emx1 and Emx2, are related toempty spiracles, and two genes, termed Otx1 and Otx2, are related toorthodenticle. These genes are all expressed in the developing rostral brain of E10 mouse embryos and their expression domains can be compared. Otx2 is expressed in all dorsal and most ventral regions of telencephalon, diencephalon, and mesencephalon. The Otx1 expression domain is similar to that of Otx2, but smaller and contained within it. The Emx2 expression domain is comprised of dorsal telencephalon and small diencephalic regions, both dorsally and ventrally. Finally, Emx1 expression is exclusively confined to the dorsal telencephalon. At the time when regional specification of major brain regions takes place, the expression domains of the four genes appear to be continuous regions contained within each other in the sequence Emx1

ISSN:0022-3034    

DOI:10.1002/neu.480241008

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractIn recent years, the discovery of Pax genes in mouse has played an invaluable role in furthering our understanding in mouse developmental processes and disorders. To date, eight murine paired box‐containing genes have been cloned. Seven of these exhibit a distinct spationtemporal expression pattern in the developing nervous system implying a role in the regional specification of the developing spinal cord and brain. The Pax genes encode for sequence‐specific DNA binding transcription factors that play a key role in embryonic development. Three of these developmental control genes are altered in mutant mice and two are associated with human diseases. Disruption of these Pax genes leads to abnormalities in neural crest derivatives, neuroectoderm, sclerotome or myotome‐derived tissues. Disruption of thePax‐3gene causes theSplotchphenotype in mice and Waardenburg syndrome in humans.Pax‐6mutations result inSmall eyemice and the human genetic disorder aniridia. ThePax‐1gene is mutated inundulatedmice. Pax proteins can transform cells in culture which then form tumours following injection in nude mice. Consistent with this activity,PAX3has been recently implicated in the generation of the tumour alveolar rhabdomyosarcoma. © 1993 John Wil

ISSN:0022-3034    

DOI:10.1002/neu.480241009

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractMembers of the vertebrateDlx‐ andNKx2‐homeobox‐containing gene families exhibit closely related, comple‐mentary areas of gene expression in the developing forebrain. The expression domains and onset of gene transcription indicate that these genes may play a role in forebrain patterning, particularly in the diencephalon. In some cases, gene expression borders coincide with mor‐phological boundaries separating functional and anatomical regions of the forebrain suggesting that the rostral region of the neural tube may indeed arise from a segmented structure. © 1993 John Wiley

ISSN:0022-3034    

DOI:10.1002/neu.480241010

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractPositional identity in the visual system affects the topographic projection of the retina onto its central targets. In this review we discuss gradients and positional information in the retina, when and how they arise, and their functional significance in development. When the axons of retinal ganglion cells leave the eye, they navigate through territory in the central nervous system that is rich in positional information. We review studies that explore the navigational cues that the growth cones of retinal axons use to orient towards their target and organize themselves as they make this journey. Finally, these axons arrive at their central targets and make a precise topographic map of visual space that is crucial for adaptive visual behavior. In the last section of this review, we examine the topographic cues in the tectum, what they are, when, and how they arise, and how retinal axons respond to them. We also touch on the role of neural activity in the refinement of this topography. © 1993 John Wiley&Sons, Inc

ISSN:0022-3034    

DOI:10.1002/neu.480241011

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY