RESUMO
The gene poxn codes for a transcriptional regulator that specifies poly-innervated (chemosensory), as opposed to mono-innervated (mechanosensory), organs in Drosophila. The ectopic expression of poxn during metamorphosis results in a transformation of the morphology and central projection of adult mechanosensory organs toward those of chemosensory organs. Here we show, by electron microscopy analysis of normal and transformed bristles and by Dil labeling of the innervating neurons, that poxn also controls the number of neurons. To determine whether poxn can transform not only the sense organ precursor cells but also their daughter cells, we examine the effects of the ectopic expression of poxn at different stages of the lineage, and we conclude that poxn can act at a late stage to affect the fate of the undifferentiated neuron.
Assuntos
Células Quimiorreceptoras/fisiologia , Drosophila melanogaster/genética , Drosophila melanogaster/fisiologia , Mecanorreceptores/fisiologia , Neurônios Aferentes/fisiologia , Animais , Diferenciação Celular , Linhagem Celular , Expressão Gênica , Proteínas de Choque Térmico/biossíntese , Mecanorreceptores/ultraestrutura , Neurônios Aferentes/citologia , Neurônios Aferentes/metabolismoRESUMO
The formation of a sense organ in Drosophila is a progressive process which begins with the local acquisition of a 'proneural' state. Mutations altering different steps of this process reveal the existence of several distinct operations, some of which are mediated by transcriptional regulation while others involve cell interactions.
Assuntos
Drosophila/crescimento & desenvolvimento , Animais , Comunicação Celular , Drosophila/genética , Drosophila/metabolismo , Feminino , Genes , Masculino , Morfogênese , Mutação , Sistema Nervoso/crescimento & desenvolvimento , Transcrição GênicaRESUMO
What is the nature of the genetic programme that allows neurons to extend their axons and connect to other neurons with a high degree of specificity? Work on the sensory neurons of the fly has shown how the control of neuronal identity is embedded in the general developmental programme of the organism. The ongoing analysis of pathfinding mutants suggests plausible mechanisms for the translation of neuronal identity into axonal behaviour.
Assuntos
Drosophila/genética , Neurônios/fisiologia , Órgãos dos Sentidos/crescimento & desenvolvimento , Animais , Axônios/fisiologia , Drosophila/crescimento & desenvolvimento , Regulação da Expressão Gênica no Desenvolvimento , Mutação , Neurônios Aferentes/fisiologiaRESUMO
A major issue in development is to understand how local heterogeneities are interpreted to determine specific cell fates. The sense organs of Drosophila provide an accessible system for addressing this issue. Most sense organs comprise four types of cells, and their differentiation is the outcome of a complex developmental programme comprising several steps. Recent results illuminate, for several of these steps, the nature of the local heterogeneities and the mechanism used to interpret them in terms of cell fate decisions.
Assuntos
Drosophila/embriologia , Órgãos dos Sentidos/embriologia , Animais , Linhagem Celular , Drosophila/citologia , Ectoderma/fisiologia , Órgãos dos Sentidos/citologiaRESUMO
Genetic analysis of development in Drosophila melanogaster has advanced our understanding of "position reading", where the expression of particular genes informs a cell of its position in the developing animal. The first step in localization of fly sense organs is the local expression of a gene conferring neural competence on epidermal cells. The four genes of the achaete-scute (AS-C) complex play crucial roles in the localization of sense organs. The resolution of local expression of AS-C genes along one dimension is about 10%; accuracy is improved by the balancing local expression of AS-C antagonist genes such as extramacrochaete. Position reading seems to depend primarily on such patterns of gene expression, and not upon the compartmental identity of the cells. No evidence has been found for differing roles of the four AS-C genes in the generation of sense organ progenitor cells or in the specification of neuronal properties of innervating neurons. The formation of each sense organ may be a unique case where the different proneural and neurogenic gene products have varying importance, and fortuitous local effects acting on this complex combination of factors have come to be important. The fly may be evolving from a flexible regular pattern to an inflexible irregular pattern strongly dependent on local factors, turning the fly into a crystallized system. (Written by R. Wayne Davies.).
Assuntos
Drosophila melanogaster/genética , Expressão Gênica , Órgãos dos Sentidos/embriologia , Animais , Embrião não MamíferoRESUMO
The lateral line of fish and amphibians is a sensory system that comprises a number of individual sense organs, the neuromasts, arranged in a defined pattern on the surface of the body. A conspicuous part of the system is a line of organs that extends along each flank (and which gave the system its name). At the end of zebrafish embryogenesis, this line comprises 7-8 neuromasts regularly spaced between the ear and the tip of the tail. The neuromasts are deposited by a migrating primordium that originates from the otic region. Here, we follow the development of this pattern and show that heterogeneities within the migrating primordium prefigure neuromast formation.
Assuntos
Regulação da Expressão Gênica no Desenvolvimento , Neurônios/fisiologia , Animais , Linhagem da Célula , Movimento Celular , Núcleo Celular/metabolismo , Dextranos/farmacologia , Fluoresceína/farmacologia , Corantes Fluorescentes/farmacologia , Células Ciliadas Auditivas/metabolismo , Hibridização In Situ , Microscopia de Vídeo , Mitose , Fatores de Tempo , Raios Ultravioleta , Peixe-ZebraRESUMO
How can the development of an ordered array of neuronal connections be encoded in the genome? Results on the establishment of sensory connections in insects indicate that this programming is a multi-stepped process which begins as soon as the first axons develop. Because each step relies on the previous level of organization, the first steps of the process are subject to intense structural constraints, and therefore have been largely conserved through evolution. What is known of the molecular biology of some essential steps, like the differentiation of excitable cells, their aggregation in nerve cords, and the diversification of a periodic structure, supports the idea that the basic organization of the CNS evolved before the divergence between the chordate and the arthropod/annelid lineage.
Assuntos
Sistema Nervoso/embriologia , Animais , Evolução Biológica , Aves/embriologia , Drosophila/embriologia , Gafanhotos/embriologia , Neurônios Motores , Neurônios Aferentes , Platelmintos/embriologiaRESUMO
The bithorax complex (BX-C) comprises several genes required for the diversification of posterior segments in Drosophila. The BX-C genes control segment differences not only in the epidermis but in other tissues as well, especially in the central nervous system. We have examined the control of one segment-specific neural structure: the lateral dots, a paired structure present in the first abdominal segment of the larval CNS and absent in all following abdominal segments. Our results show that the suppression of lateral dots in segments A3 and A4 requires the presence of two active copies of one of the BX-C genes, abdominal-A (abd-A). We also show that the adjacent BX-C regions, iab-3 and iab-4, can act in trans on abd-A not only when the two copies of BX-C are paired but also, at least to some extent, when pairing is disturbed.
Assuntos
Drosophila/embriologia , Animais , Sistema Nervoso Central/embriologia , Drosophila/genética , Genes Homeobox , Morfogênese , FenótipoRESUMO
We have recently described the identification of a gene, tap, which encodes a bHLH protein expressed in one neuron of each larval chemosensory organ. Here we show that tap is expressed at a late stage in the development of one type of adult chemosensory organ, the gustatory bristles of the leg, wing and proboscis. We also show that tap is expressed very early in the development of a second type of chemosensory receptors, the olfactory organs of the antenna. The results of behavioral experiments suggest that the ectopic expression of tap affects the response to sugar and salt.
Assuntos
Células Quimiorreceptoras/fisiologia , Sistema Digestório/crescimento & desenvolvimento , Proteínas de Drosophila , Drosophila/crescimento & desenvolvimento , Sequências Hélice-Alça-Hélice , Proteínas de Insetos/biossíntese , Proteínas de Insetos/fisiologia , Neuropeptídeos/biossíntese , Neuropeptídeos/fisiologia , Condutos Olfatórios/crescimento & desenvolvimento , Fatores de Transcrição , Animais , Sistema Digestório/inervação , Fenômenos Fisiológicos do Sistema Digestório , Drosophila/metabolismo , Larva/crescimento & desenvolvimento , Larva/metabolismo , Metamorfose Biológica , Neurônios/fisiologia , Condutos Olfatórios/fisiologiaRESUMO
The tactile bristles of the fly comprise four cells that originate from a single precursor cell through a fixed lineage. The gene tramtrack (ttk) plays a crucial role in defining the fates of these cells. Here we analyse the normal pattern of expression of ttk, as well as the effect of ttk overexpression at different steps of the lineage. We show that ttk is never expressed in cells having a neural potential, and that in cells where ttk is expressed, there is a delay between division and the onset of expression. The ectopic expression of ttk before some stage of the cell cycle can block further cell division. Furthermore, this expression transforms neural into non-neural cells, suggesting that ttk acts as a repressor of neural fate at each step of the lineage. Our results suggest that ttk is probably not involved in setting up the mechanism that creates an asymmetry between sister cells, but rather in the implementation of that choice.
RESUMO
We have isolated a Drosophila bHLH gene, tap, that is expressed in a small subset of neurons when they undergo differentiation. In the peripheral nervous system, tap is expressed exclusively in one of the neurons that innervate each larval chemosensory organ, possibly controlling the specific properties of that neuron. Sequence comparisons suggest that tap is most closely related to two bHLH genes identified in several vertebrate species, neurogenin and neuroD, which are involved respectively in neural determination and in neuronal differentiation.
Assuntos
Proteínas de Caenorhabditis elegans , Proteínas de Drosophila , Sequências Hélice-Alça-Hélice , Proteínas de Insetos/genética , Neuropeptídeos/genética , Fatores de Transcrição , Sequência de Aminoácidos , Animais , Sequência de Bases , Caenorhabditis , DNA Complementar , Drosophila/genética , Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Helminto/química , Proteínas de Insetos/química , Proteínas com Homeodomínio LIM , Camundongos , Camundongos Endogâmicos BALB C , Dados de Sequência Molecular , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/metabolismo , Neurônios/metabolismo , Neuropeptídeos/química , Fatores de Transcrição Box Pareados , Órgãos dos Sentidos/metabolismo , Análise de Sequência de DNA , Homologia de Sequência de AminoácidosRESUMO
Intrabodies show great promise for controlling gene expression. As an initial attempt to evaluate the intrabody technology in Drosophila, the gene poxn was used as target. Transgenic flies harboring different anti-Poxn scFv genes integrated into various chromosomes were obtained. In one transformant, a phenocopy resembling the hypomorphic poxn-phenotype was produced in embryos and larvae following induction of expression of alpha-Poxn2 intrabody. The antisense approach was used as control. Parameters that can affect the success of intrabody technology are described.
Assuntos
Proteínas de Drosophila , Fragmentos de Imunoglobulinas , Mutação , Proteínas do Tecido Nervoso/genética , Fatores de Transcrição , Animais , Animais Geneticamente Modificados , DNA Antissenso , Drosophila/genética , Regulação da Expressão Gênica , Temperatura Alta , Fatores de Transcrição Box Pareados , Fenótipo , TransfecçãoRESUMO
The usefulness of intrabodies as specific inhibitors of gene function has been extensively demonstrated in cell culture assays. However, very few experiments have been conducted with intrabodies expressed in whole organisms. To evaluate the intrabody technology in Drosophila, we focused on poxn protein, since its effects can be easily studied. We purified the recombinant poxn protein. We next isolated three single-chain variable fragments (scFv) which specifically recognize poxn protein. Two scFvs, designated alpha-Poxn2 and alpha-Poxn4, react with both denatured and native Poxn with half maximal inhibition values of 100 nM and 40 nM, respectively. The alpha-Poxn5 scFv also recognizes denatured Poxn but either does not recognize native Poxn or its half maximal inhibition value for native Poxn is high.
Assuntos
Proteínas de Drosophila , Genes de Imunoglobulinas , Região Variável de Imunoglobulina/genética , Proteínas do Tecido Nervoso/imunologia , Fatores de Transcrição , Animais , Anticorpos Monoclonais/isolamento & purificação , Especificidade de Anticorpos , Clonagem Molecular , Drosophila/química , Escherichia coli/genética , Estudos de Avaliação como Assunto , Camundongos , Camundongos Endogâmicos NZB , Camundongos Endogâmicos , Proteínas do Tecido Nervoso/genética , Fatores de Transcrição Box Pareados , Proteínas Recombinantes/isolamento & purificaçãoRESUMO
We examined the efferent innervation of the lateral line in zebrafish larvae. Three efferent nuclei were previously reported for the posterior line, two in the hindbrain and one in the ventral hypothalamus. Here we show that the same three nuclei innervate the anterior line as well. The rhombencephalic neurons innervate either the anterior or the posterior line. The diencephalic neurons seem to innervate both lines as well as the ear. The diencephalic efferents are labeled by anti-tyrosine hydroxylase antibodies and probably use dopamine as a transmitter. They are among the very first catecholaminergic neurons to differentiate in the brain and extend branches into the lateral line system almost as soon as the latter forms. We discuss possible functions of the rhombencephalic and diencephalic efferents.
Assuntos
Hipotálamo/citologia , Mecanorreceptores/citologia , Rombencéfalo/citologia , Órgãos dos Sentidos/inervação , Peixe-Zebra/anatomia & histologia , Animais , Dextranos , Fluoresceínas , Hipotálamo/crescimento & desenvolvimento , Indicadores e Reagentes , Larva/anatomia & histologia , Mecanorreceptores/crescimento & desenvolvimento , Neurônios Eferentes/enzimologia , Rombencéfalo/crescimento & desenvolvimento , Órgãos dos Sentidos/crescimento & desenvolvimento , Medula Espinal/citologia , Medula Espinal/crescimento & desenvolvimento , Tirosina 3-Mono-Oxigenase/análiseRESUMO
The neurons innervating insect sense organs vary in number, shape, dendritic morphology, axonal projections and connectivity, providing abundant material for the genetic analysis of neuronal diversity. Here we describe the leg of Drosophila as a potential model system for this analysis. The leg of Drosophila comprises a variety of sense organs arranged in a precise and reproducible pattern. The cell bodies of the sensory neurons are located near the organ they innervate, which greatly facilitates their identification and accessibility. The development of the leg from its progenitor structure, the imaginal disc, is known in good detail. In particular, the time of appearance and of divisions of the sense organ precursors is known. The origin and mode of formation of the leg nerve (through which all sensory axons project into the central nervous system) has been described. The central projections of some of the sensory neurons have been examined by horseradish peroxidase backfill or DiI labelling. Finally, the expression of several genes that control the differentiation of various types of sensory neurons can be manipulated at will. We illustrate these different aspects, and discuss the potentials and shortcomings of this system.
Assuntos
Drosophila/embriologia , Drosophila/fisiologia , Extremidades/embriologia , Extremidades/inervação , Neurônios/fisiologia , Animais , Células Quimiorreceptoras/fisiologia , Proteínas de Choque Térmico HSP70/biossíntese , Temperatura Alta , Mecanorreceptores/fisiologia , Modelos Neurológicos , Vias Neurais/fisiologia , Neurônios/ultraestrutura , Neurônios Aferentes/ultraestrutura , Órgãos dos Sentidos/embriologia , Órgãos dos Sentidos/fisiologia , Coloração e RotulagemRESUMO
The formation of sense organs in Drosophila involves a series of choices, each of which depends on the co-ordinated activity of a small battery of genes. Two essential steps of this process have been extensively studied over the past few years: the determination of neural precursor cells, and their diversification. In both cases, the choices are dichotomous, and each choice reflects the fact that a specific control gene is or is not expressed. This principle is illustrated in the case of the genes "cut" and "poxn", the expression of which controls the type of sense organ that a given precursor will form.
Assuntos
Drosophila/crescimento & desenvolvimento , Sistema Nervoso/crescimento & desenvolvimento , Animais , Diferenciação Celular , Drosophila/citologia , Drosophila/genética , Neurônios/fisiologia , Órgãos dos Sentidos/crescimento & desenvolvimentoAssuntos
Escherichia coli/análise , Mutação , RNA de Transferência/análise , Aminoácidos/análise , Sequência de Bases , Radioisótopos de Carbono , Colífagos , Eletroforese em Gel de Poliacrilamida , Glutamina , Lisogenia , Nitrosoguanidinas , Nucleotídeos , Radioisótopos de Fósforo , RNA Bacteriano/análise , Recombinação Genética , Supressão Genética , TirosinaRESUMO
An analysis of the central projection of various sensory neurones in the homoeotic mutant bithorax postbithorax, and in flies where an adult nerve had been experimentally misrouted, reveals that neurones are able to develop a normal projection even if they enter the central nervous system at an unusual place.