GENETIC CONTROL OF MONAMINERGIC AXON GROWTH

拟议中的实验将调查遗传和环境 影响哺乳动物发育中正常轴突生长的机制 神经系统。我们将检验3个基本假设：1)基因 神经元可以控制轴突的生长，2)基因调节神经元的反应性 神经元对调节轴突生长和3)基因缺陷的外在线索的反应 改变轴突生长导致正常的特定代偿性改变 系统的一部分。一个基于单基因座基因的模型系统 突变，将用于：蓝斑(LC)去甲肾上腺素能神经元 纯合子突变小鼠摇摇欲坠(Tg/Tg)是一组明确的神经 靶区轴突旺盛生长的细胞是由单一的 基因座基因突变。我们将在眼胎LC中移植来自 TG/TG和正常(+/+)小鼠确定基因突变是否发生改变 轴突生长直接影响内在的发育调节 LC神经元的机制。基因缺陷的内在本质会 在TG/TG+/+嵌合体中也进行了评估，使用双重标记方法 结合原位杂交或酶组织化学和 免疫细胞化学以同时鉴定基因和表型。我们 将确定单基因座基因突变是否改变了 LC神经元对靶点提供的环境线索的反应能力 或其他通常有助于轴突调节的纤维系统 通过使用双倍(LC和目标)和三倍(LC、目标和 另一种纤维系统)移植范例。补偿性的 LC传入神经元对轴突异常增殖的反应 采用形态定量超微结构分析方法进行研究。这个 该基因在影响轴突形成中的相对贡献将是 通过以一种独特的方式结合不同的实验系统来观察。 这些研究可能为分析纤维生长提供合理的策略 发育异常发育中或受伤后的异常

The proposed experiments will investigate the genetic and environmental mechanisms that affect normal axon growth in the developing mammalian nervous system. We will test 3 basic hypotheses: 1) Genes intrinsic to a neuron can control axon growth, 2) Genes regulate the responsiveness of neurons to extrinsic cues that modulate axon growth and 3) Gene defects that alter axon growth result in specific compensatory changes in normal parts of the system. A model system, based on a single locus gene mutation, will be used: The locus coeruleus (LC) noradrenergic neurons in the homozygous mutant mouse tottering (tg/tg) are a defined group of nerve cells whose exuberant axon growth in target areas is caused by a single locus gene mutation. We will transplant in oculo fetal LC neurons from tg/tg and normal (+/+) mice to determine whether the gene mutation altering axon growth affects directly an intrinsic developmental regulatory mechanisms in LC neurons. The intrinsic nature of the gene defect will also be assessed in tg/tg +/+ chimeras, using double labeling methods that combine in situ hybridization or enzyme histochemistry and immunocytochemistry to identify simultaneously genotype and phenotype. We will determine whether the single locus gene mutation has altered the ability of LC neurons to respond to environmental cues provided by targets or other fiber systems that normally contribute to the regulation of axon growth by the use of double (LC and target) and triple (LC, target and another fiber system) transplantation paradigms. The compensatory responses of LC afferents to the abnormal axon proliferation will be investigated using quantitative morphometric ultrastructural analysis. The relative contribution of the gene in influencing axongenesis will be observed by combining in a unique fashion different experiment systems. These studies may provide rational strategies for analyzing fiber growth abnormalities in development or following injury.