NEURON DIFFERENTIATION IN C ELEGANS

线虫中的神经元分化

• 批准号: 6540117
• 负责人: SCOTT W EMMONS
• 金额: $ 25.62万
• 依托单位: ALBERT EINSTEIN COLLEGE OF MEDICINE
• 依托单位国家: 美国
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-07-16 至 2003-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6540117
• 关键词: Caenorhabditis elegans; bone morphogenetic proteins; cell differentiation; developmental genetics; developmental neurobiology; dopamine; fibroblast growth factor; gene interaction; genetic promoter element; genetic regulatory element; genetic screening; green fluorescent proteins; heat stimulus; homeobox genes; lasers; neuronal guidance; neurons; phenotype; reporter genes

DESCRIPTION (from applicant's abstract): This application examines how a neuron is specified to express a defined set of differentiated characteristics. Dr. Emmons has been examining the morphogenesis of the male tail in the nematode C. elegans. The male tail is composed of nine morphologically distinct pairs of rays in an acellular fan. The 3 cells of each ray, 2 neurons and a structural cell are derived from a ray precursor cell, Rn. By characterizing mutants with abnormal tail morphologies, several genes responsible for tail morphogenesis have been identified. Repeated expression of the ray sublineage is dependent on expression of lin-32, a bHLH transcription factor of the achaete/scute family. Differences among the rays are dependent on several transcription factors of the C. elegans Hox cluster, mab-5, egl-5, and Pax-6. The expression of these transcription factors may be regulated by extracellular factors. One extracellular factor that is involved in ray 5, 7, and 9 formation is dbl-1, which encodes a BMP2 homolog. Dbl-1 may act through SMA-6 and DAF-4, type I and type II BMP receptors, respectively, and the products of the sma-2, sma-3, and sma-4, which are SMAD proteins. Among the differentiated characteristics of neurons is the expression of their complement of transmitters. Dr. Emmons proposes to focus on how neurotransmitter phenotype is specified, and will examine the specification of dopamine (DA) in three bilateral pairs of sensory neurons in rays 5, 7, and 9 of the male tail. Transgenic animals carrying a TH::GFP reporter construct were examined in dbl-1, sma-3, egl-5, and mab-21 loss of function backgrounds. These animals expressed GFP ectopically in other rays, suggesting that the expression of DA is independent of BMP but DA patterning is dependent on BMP. Overexpression of the DBL-1 protein by a hs::dbl-1 transgene resulted in GFP expression in rays 3-9, but never in rays 1 or 2. These data suggest that DBL-1 may provide instructive cues. Since no expression is seen in rays 1 or 2, these rays may be incompetent to respond to the DBL-1 signal. The investigator proposes the model that DA specification is based on three patterning processes: patterned expression of the ligand (DBL-1), pre-patterning of cell competence by egl-5 and some other unidentified gene, and lateral inhibition. The aims of this application are to: (1) examine the role of DBL-1, Hox genes, and other genes in inducing DA phenotype. TH::GFP expression will be examined in animals with mutations in BMP and Hox genes. This will determine whether all cells have equal competence to take on a DA phenotype, to distinguish between whether ray cells are prepatterned to respond to BMP or whether BMP is spatially patterned, and to determine whether Hox genes play a role in establishing competence to cells to respond to the BMP signal. It will also be determined whether there is an inhibitory pathway restricting DA expression. Animals with mutations in mab-21, which encodes a novel protein, will be examined for TH::GFP expression; wild-type animals will also be ablated for different ray precursor cells. (2) determine whether common cis-regulatory elements are present in genes involved in DA synthesis. Promoter regions necessary for DA expression in rays will be delimited and examined for conserved motifs. (3) screen for mutants (including ts alleles) in which TH::GFP expression is lost and characterize the corresponding genes molecularly. (4) identify genes involved in the axon connectivity of DA neurons.

描述（来自申请人的摘要）：这个应用程序研究如何指定一个神经元来表达一组已定义的差异化特征。埃蒙斯博士一直在研究线虫（C. elegans）雄性尾巴的形态发生。雄鱼的尾巴由九对形态上截然不同的鳐鱼组成，呈无细胞扇形。每条射线的3个细胞、2个神经元和1个结构细胞来源于射线前体细胞Rn。通过对尾巴形态异常突变体的特征分析，已经确定了几个与尾巴形态发生有关的基因。射线亚谱系的重复表达依赖于lin-32的表达，lin-32是一种无毛/鳞片家族的bHLH转录因子。射线之间的差异取决于秀丽隐杆线虫Hox簇的几个转录因子，mab-5， egl-5和Pax-6。这些转录因子的表达可能受到细胞外因子的调控。一个参与射线5、7和9形成的细胞外因子是dbl-1，它编码BMP2同源物。Dbl-1可能分别通过I型和II型BMP受体SMA-6和DAF-4以及SMAD蛋白sma-2、sma-3和sma-4的产物起作用。神经元的分化特征之一是其补体递质的表达。埃蒙斯博士建议把重点放在神经递质表型是如何被指定的，并将检查多巴胺（DA）在雄性尾巴射线5、7和9的三对双侧感觉神经元中的指定。携带TH::GFP报告基因构建的转基因动物在dbl-1、sma-3、egl-5和mab-21功能缺失背景下进行了检测。这些动物在其他射线中异位表达GFP，表明DA的表达与BMP无关，但DA的模式依赖于BMP。通过hs:: DBL-1转基因过表达DBL-1蛋白可在射线3-9中表达GFP，但在射线1和射线2中不表达。这些数据表明，DBL-1可能提供了有益的线索。由于在射线1或射线2中未见表达，这些射线可能对DBL-1信号没有反应。研究者提出了DA规范基于三个模式过程的模型：配体（DBL-1）的模式表达，egl-5和其他未知基因对细胞能力的预模式，以及侧抑制。本应用程序的目的是：(1)检查DBL-1， Hox基因和其他基因在诱导DA表型中的作用。将在BMP和Hox基因突变的动物中检测TH::GFP的表达。这将决定是否所有细胞都具有相同的DA表型能力，以区分射线细胞是对BMP作出反应的预模式还是BMP是空间模式，并确定Hox基因是否在建立细胞对BMP信号作出反应的能力中发挥作用。是否存在限制DA表达的抑制通路也将被确定。编码一种新蛋白的mab-21突变的动物将被检测TH::GFP表达；野生型动物也将被切除不同的射线前体细胞。(2)确定参与DA合成的基因中是否存在共同的顺式调控元件。射线中DA表达所需的启动子区域将被划定并检查保守的基序。(3)筛选TH::GFP表达缺失的突变体（包括ts等位基因），并对相应基因进行分子表征。(4)确定与DA神经元轴突连通性相关的基因。