A Novel System to Study Postsynaptic Molecules that Affect Presynaptic Function

描述（由申请人提供）：神经递质释放的活动依赖调节，称为短期可塑性，与多种形式的行为、学习和记忆有关。虽然短期可塑性是由突触前机制介导的，但许多突触的短期可塑性是靶细胞特异性的。因此，由同一细胞类型的轴突与不同类型的目标神经元形成的突触可以表现出明显不同的短期可塑性特性。这意味着存在从突触后神经元到突触前细胞的逆行信号，该信号根据突触后目标神经元的身份改变突触前末端的结构和/或功能。虽然人们已经知道突触前功能是靶细胞特异性的，但这种逆行信使的身份仍然不清楚。该项目的长期目标是确定负责靶细胞特异性短期可塑性的突触后分子。突触细胞粘附分子神经素1和SynCAM在共培养的非神经元细胞中表达可诱导神经元突触前分化。这表明，即使在突触后末端缺乏其他正常成分的情况下，神经素1和SynCAM也足以触发突触前分化。虽然神经素1和SynCAM已被证明足以诱导神经元（这里称为半突触）中突触前终末的形成，这些终末在基本水平上具有功能，但尚不清楚它们是否足以使半突触的突触前终末具有与神经元-神经元突触相同的复杂突触前特性。特别是，以前没有显示它们是否能够诱发神经递质释放，如果是的话，它们是否具有与神经元突触相似的释放概率和短期可塑性机制。在本提案中，我们将开发半突触制备和测量诱发的神经递质释放和短期可塑性，以验证触发突触形成的细胞粘附分子也参与调节突触前末端功能特性的逆行信号传导，但不足以诱导形成具有神经元-神经元突触所有相同特性的突触前末端的假设。该系统将为未来研究特定细胞粘附分子、细胞外基质蛋白、神经营养因子、分泌因子和突触后密度成分对突触前终末形成和功能的影响的大范围实验提供一种简单而强大的分析方法。这些实验解决了突触前功能、突触特化和发育的基本问题，这些问题对我们理解大脑回路非常重要，并将对学习和记忆以及导致智力迟钝的神经退行性疾病和发育障碍产生影响。这些实验解决了突触前功能、突触特化和发育的基本问题，这些问题对我们理解大脑回路非常重要，并将对学习和记忆以及导致智力迟钝的神经退行性疾病和发育障碍产生影响。

DESCRIPTION (provided by applicant): Activity dependent modulation of neurotransmitter release, called short-term plasticity, has been implicated in several forms of behavior and learning and memory. Although it is mediated by presynaptic mechanisms, short-term plasticity has been shown at many synapses to be target-cell specific. Thus synapses made by axons from the same cell type onto target neurons of different types can exhibit markedly different properties of short-term plasticity. This implies the existence of a retrograde signal from the postsynaptic neuron to the presynaptic cell which alters the structure and/or function of the presynaptic terminal depending on the identity of the postsynaptic target neuron. While it has been known for over 30 years that presynaptic function is target cell specific, the identity of this retrograde messenger(s) is still not known. The long term goal of this project is to determine the postsynaptic molecules that are responsible for target-cell specific short-term plasticity. The synaptic cell adhesion molecules neuroligin 1 and SynCAM have recently been shown to induce presynaptic differentiation in neurons when expressed in non-neuronal cells in co-culture. This shows that neuroligin 1 and SynCAM are sufficient to trigger presynaptic differentiation, even in the absence of other normal components of the postsynaptic terminal. While neuroligin 1 and SynCAM have each been shown to be sufficient to induce formation of presynaptic terminals in neurons (referred to here as hemisynapses) that are functional at a basic level, it is not known whether they are sufficient to enable presynaptic terminals of hemisynapses to have the same complex presynaptic properties that neuron-neuron synapses possess. In particular, has not previously been shown whether they are capable of evoked neurotransmitter release, and if so, whether they have a similar release probability and mechanisms of short-term plasticity as neuron-neuron synapses. In this proposal, we will develop the hemisynapse preparation and measure evoked neurotransmitter release and short-term plasticity, in order to test the hypothesis that the cell adhesion molecules that trigger synapse formation are also involved in the retrograde signaling that modulates the functional properties of presynaptic terminals, yet are not sufficient to induce formation of presynaptic terminals with all of the same properties of neuron- neuron synapses. This system will provide a simple but powerful assay for a large range of future experiments investigating the influences of specific cell adhesion molecules, extracellular matrix proteins, neurotrophins, secreted factors, and postsynaptic density components on the formation and function of presynaptic terminals. These experiments address fundamental questions of presynaptic function, synaptic specialization and development that are important to our understanding of circuits in the brain, and which will have implications for learning and memory as well as neurodegenerative diseases and developmental disorders that cause mental retardation. These experiments address fundamental questions of presynaptic function, synaptic specialization and development that are important to our understanding of circuits in the brain, and which will have implications for learning and memory as well as neurodegenerative diseases and developmental disorders that cause mental retardation.