ISSN:0022-3034    

DOI:10.1002/neu.480240602

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

年代:1993

数据来源: WILEY

摘要:

AbstractMany of the steps involved in formation of theDrosophilaembryonic central nervous system (CNS) have been identified by both descriptive and experimental studies. In this review we will describe the various approaches that have been used to identify molecules involved in CNS development and the advantages and disadvantages of each of them. Our discussion will by no means be exhaustive; but rather we will discuss our experiences with each approach and provide an overview of what has been learned by using these methodologies. Finally, we will discuss methods that have been recently developed and how they are likely to provide further insight into CNS development. © 1993 John Wiley&Sons, Inc

ISSN:0022-3034    

DOI:10.1002/neu.480240603

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

年代:1993

数据来源: WILEY

摘要:

AbstractRegulated gene activity is crucial to the formation and function of the nervous system. It is well known that gene regulation can occur at the transcriptional, post‐transcriptional, translational, and post‐translational levels. In this review our focus has been on the post‐transcriptional regulation in neurons and on neural‐specific RNA binding proteins that may be involved in post‐transcriptional modulation of gene activity. We have taken advantage of this opportunity to review our work on theelavgene ofDrosophila melanogasterwhich encodes a neural‐specific RNA binding protein and relate it to other members of thiselav‐like gene family. We report new data that suggests thatelavis post‐transcriptionally regulated and we demonstrate that below‐threshold levels of ELAV protein severely affects neuronal differentiation. © 1993 Jo

ISSN:0022-3034    

DOI:10.1002/neu.480240604

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

年代:1993

数据来源: WILEY

摘要:

AbstractNervous systems of higher organisms are comprised of a variety of cell types which are interconnected in a precise manner. The molecular mechanisms that lead to the specification of neuronal cell types are not well understood. The compound eye of the fruit flyDrosophilais an attractive experimental system to understand these mechanism. The compound eye is a reiterated neural pattern with several hundred unit structures and is amenable to both classical and molecular genetic methods. During the development of the compound eye cell–cell interactions and positional information play a critical role in the determination of cell fate. Recent genetic and molecular studies have provided important clues regarding the nature of the molecules involved in cellular signalling and neuronal differentiation. © 1993 John Wiley&Sons, I

ISSN:0022-3034    

DOI:10.1002/neu.480240605

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe neuromuscular connections ofDrosophilaare ideally suited for studying synaptic function and development. Hypotheses about cell recognition can be tested in a simple array of pre‐and postsynaptic elements.Drosophilamuscle fibers are multiply innervated by individually identifiable motoneurons. The neurons express several synaptic cotransmitters, including glutamate, proctolin, and octopamine, and are specialized by their synaptic morphology, neurotransmitters, and connectivity. During larval development the initial motoneuron endings grow extensively over the surface of the muscle fibers, and differentiate synaptic boutons of characteristic morphology. While considerable growth occurs postembryonically, the initial wiring of motoneurons to muscle fibers is accomplished during mid‐to‐late embryogenesis (stages 15–17). Efferent growth cones sample multiple muscle fibers with rapidly moving filopodia. Upon reaching their target muscle fibers, the growth cones rapidly differentiate into synaptic contacts whose morphology prefigures that of the larval junction. Mismatch experiments show that growth cones recognize specific muscle fibers, and can do so when the surrounding musculature is radically altered. However, when denied their normal targets, motoneurons can establish functional synapses on alternate muscle fibers. Blocking synaptic activity with either injected toxins or ion channel mutants does not derange synaptogenesis, but may influence the number of motor ending processes. The molecular mechanisms governing cellular recognition during synaptogenesis remain to be identified. However, several cell surface glycoproteins known to mediate cellular adhesion eventsin vitroare expressed by the developing synapses. Furthermore, enhancer detector lines have identified genes with expression restricted to small subsets of muscle fibers and /or motoneurons during the period of synaptogenesis. These observations suggest that inDrosophilaa mechanism of target chemoaffinity may be involved in the genesis of stereotypic synaptic wiring. © 1993 John Wiley&S

ISSN:0022-3034    

DOI:10.1002/neu.480240606

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe imaginal wing disc of flies gives rise to the adult wing blade and dorsal thorax (notum). A great deal has been learned in recent years about the process of neurogenesis in this disc; a number of genes that play crucial roles in the formation of sensory mother cells and in the differentiation of the sensory organs have been identified and their roles defined. Given this extensive background of developmental genetics, it has seemed profitable to summarize what is known about the end‐products of neural development, the adult sensory organs. Discussed are their physiological function and role in behavior, the pathways followed by their axons in the CNS, and both genes and epigenetic processes that might play some role in the later stages of neural development and in adult function. The highly individual characteristics of certain of the sensory organs is emphasized, both in the context of their adult roles and as a challenge for future studies in developmental genetics. © 1993 John Wiley&Sons, I

ISSN:0022-3034    

DOI:10.1002/neu.480240607

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

年代:1993

数据来源: WILEY

摘要:

AbstractA combined genetic, anatomical, and behavioral approach has been undertaken to study the developmental and functional plasticity of identified bristle mechanosensory neurons inDrosophila. A stereotyped grooming reflex in decapitated flies enabled simple but reliable assessments of the functional output of individual bristle sensory cells to correlate with their axonal projections and terminal arbors revealed by the cobalt backfill technique. Construction of small‐patch mosaics that contain only a single mutant bristle allowed functional perturbation of individual neurons within an otherwise normal environment. Mutations that affect nerve excitability and membrane recycling have been used to examine their effects on neuronal pathfinding, arborization, and the initiation and maintenance of functional connections. Previous studies (Burg and Wu, 1986,J. Neurosci.6:2968–2976; 1989,Dev. Biol.131:505–514) have demonstrated thatparatsnaptsdouble‐mutant sensory neurons, in which action potentials are unconditionally blocked by defects in sodium currents, andeag Shdouble‐mutant sensory cells, in which membrane excitability is increased by alterations in potassium currents, can establish and maintain central projections that are indistinguishable from their functionally normal counterparts. Mutations of theshitsgene cause a temperature‐sensitive, reversible block of the membrane recycling process, resulting in arrest of neuronal growth in culture (Kim and Wu, 1987,J. Neurosci.7:3245–3255) and depletion of synaptic vesicles that leads to transmission blockade at established synapses (Ikeda, Ozawa, and Hagiwara, 1976,Nature259:489–491; Koenig and Ikeda, 1983,J. Neurobiol.14:411–419; 1989,J. Neurosci.9:3844–3860). Prolonged heat treatments (up to 16% of total development time) of small‐patchshitsmosaics at different pupal stages did not prevent the establishment of central projections characteristic of the various sensory cell types. However, none of theshitssensory neurons heat‐pulsed during the initial or the final 16% of pupal development were able to initiate the reflex behavior, although a proportion of those treated in other periods apparently established functional contacts with appropriate targets to support the characteristic cleaning reflex. The possibility exists that the membrane recycling process blocked inshitscells provides a crucial mechanism for cell–cell interactions taking place during initial differentiation and final synaptic stabilization, and possibly competition, in the developing sensory neuron. Heat treatments of adultshitsmosaics blocked the reflex initiated by the mutant (but not the surrounding normal) bristles, as expected from the effect of synaptic block. For the majority of bristle types examined, a 2‐ to 4‐h heat pulse blocked the reflex behavior for several days in younger mosaics but caused permanent loss of the reflex in mosaics older than 4 to 5 days of age. This temporal transition correlates well with the age dependence of activity‐related modification of nervous system structures (Technan, 1984,J. Neurogenet.1:113–126; Kral and Meinertzhagen, 1989,Philos. Trans. R. Soc. Lond.[Biol.] 323:155–183) and visual discrimination behavior (Mimura, 1986,Science232:83–85; 1987,Exp. Biol.46:155–162; Hirsch, Potter, Zawierucha, et al., 1990, Vis. Neurosei. 5281‐289) and may signify a “critical period” phenomenon in young adults. The results obtained from small‐patch mosaics indicate that electric activity intrinsic to the sensory neuron may not be required for its pathfinding and ramification of terminal arbors but may be important for establishing and maintaining its functional connectivity. Chemical cues either laid down by its neighboring cells or emitting and sustain its arbor since nonfunctional projections of puratsnaptssensory cells and heat‐treated shitsneurons persisted for at least 6 days in

ISSN:0022-3034    

DOI:10.1002/neu.480240608

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

年代:1993

数据来源: WILEY

摘要:

AbstractWe conducted a survey of the patterns of gene expression in the central nervous system (CNS) of larvae of the fruitflyDrosophila melanogasterto identify genes that may be important in the development of the CNS, aid in the recognition of basic organizing features that might underlie CNS development, and estimate the extent of the use of information encoded in the genome in the construction of the nervous system. A so‐called enhancer detector strategy was used to generate many thousands of lines containing a β‐galactosidase reporter gene. These lines were screened as third‐instar larvae for patterns of expression in the developing optic lobes and other portions of the CNS. Most of the lines recovered which evidence staining within the CNS could be included in one of a relatively small number of patterns. A random sample of 594 lines from the larger population screened was selected to quantify the relative frequencies of these patterns, and a more careful analysis of the changes in the patterns of expression with developmental time was done for representative lines of nine of the patterns. These studies demonstrated great variability in the patterns of gene expression as a function of developmental stage. Few, if any, lines showed β‐galactosidase activity limited to the optic lobes; similarly, few lines were identified in which staining was limited to only a small number of cells. Together with the limited number of patterns of gene expression seen, this suggests that in the larval CNS developmental pathways may be controlled by a combinatorial process of gene activity that involves the majority of the genome rather than by having a specific gene specify the fate of only a few neuronal precursors. © 1993 John Wiley

ISSN:0022-3034    

DOI:10.1002/neu.480240609

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe characteristics of the nervous systems of a number of organisms in different phyla are examined at the recombinant DNA, protein, neuroanatomic, neurophysiological, and cognitive levels. Among the invertebrates, special attention is paid to the advantages as well as the shortcomings of the flyDrosophila melanogaster, the wormCaenorhabditis elegans, the honey beeApis mellifera, the sea hareAplysia californica, the octopusOctopus vulgaris, and the squidLoligo pealei. Among vertebrates, the focus is onHomo sapiens, the mouseMus musculus, the ratRattus norvegicus, the catFelis catus, the macaque monkeyMacaca fascicularis, the barn owlTyto alba, and the zebrafishBrachydanio rerio. Vertebrate nervous systems have also been compared in fossil vs. extant organism. I conclude that complex nervous systems arose in the Early Cambrian via a big bang that was underpinned by a modular method of construction involving massive pleiotropy of gene circuits. This rapidity of construction had enormous implications for the degrees of freedom that were subsequently available to evolving nervous systems. I also conclude that at the level of neuronal populations and interactions of neuropiles there is no model system between phyla except at the basic macromolecular level. Further, I argue that to achieve a significant understanding of the functions of extant nervous systems we need to concentrate on fewer organisms in greater depth and manipulate genomes via transgenic technologies to understand the behavioral outputs that are possible from an organism. Finally, I analyze the concepts of “perceptual categorization” and “information processing” and the difficulties involved in the extrapolation of computer analogies to sophisticated nervous systems. © 1993 John Wiley&S

ISSN:0022-3034    

DOI:10.1002/neu.480240610

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.480240601

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

年代:1993

数据来源: WILEY