The role of PDZ scaffold CASK and CaMKII signaling in synaptic plasticity and learning

这一提议的目的是为了更好地了解大脑中记忆形成的分子机制。对记忆的研究特别重要，因为它给了我们认同感。学习和记忆缺陷会出现在许多疾病、损伤和衰老过程中。识别参与这些过程的关键分子，将有助于揭示新的治疗干预措施的靶点，以扭转记忆丧失的破坏性后果，这项研究对我们的老龄化人口尤为重要。大脑由许多细胞或神经元组成，这些细胞或神经元通过称为突触的连接进行通信。信息通过微小的电脉冲在神经元中流动，有点像计算机。在大多数突触中，这些电脉冲导致与输出神经元结合的化学物质的释放，使其变得更加兴奋，并将电脉冲传播到电路中的下一个神经元。大脑还在学习过程中存储信息，并将其作为记忆进行检索。大脑中有一些特殊的部分用于学习，例如海马体。当动物经历学习刺激时，海马神经元之间的突触传递持续增加，称为长时程增强(LTP)，这种增加在原始刺激消除后继续存在，是学习的突触机制。突触活动的这些长期变化可以导致突触生长和神经元之间联系的增加，这一过程被称为突触可塑性，被认为是记忆的突触机制。LTP和学习是由钙(Ca~(2+))进入神经元并激活一种称为Ca~(2+)反应激酶(CaMKII)的酶启动的。CaMKII在脑中含量丰富，占其总蛋白的1-2%，是主要的突触蛋白之一。一旦被增加的钙离子激活，CaMKII就能够引起自身活动的转换，从而即使在钙离子下降后仍保持活跃。CaMKII这种维持自身活性的特殊能力被称为分子记忆开关，是LTP和学习所必需的。CaMKII然后调节突触上其他蛋白质的活性，这些蛋白质共同维持LTP增加的突触传递。此外，CaMKII活性可以导致突触可塑性和记忆形成过程中发生的许多其他变化。这些CaMKII介导的突触可塑性变化是包括果蝇在内的大多数动物学习和记忆所必需的。尽管果蝇很小，但它们很聪明，例如，它们可以落在天花板上，检测到你的水果碗里的水果在你之前就坏了。在这项建议中，我们希望进一步利用果蝇强大的遗传学优势来研究CaMKII介导的突触学习和记忆机制。我们想要回答的一个重要问题是：在学习过程中，CaMKII的活动是如何调节和定位于突触的？我们发现，在果蝇中，就像哺乳动物一样，在低钙水平的不活跃突触上，CaMKII可以通过第二种机制来调节自己的活动，这种机制往往会使CaMKII失活。我们发现了一种新的蛋白质，它在飞行突触与CaMKII相互作用，称为CAASK，它往往会使CaMKII失活，从而破坏CaMKII经历分子记忆开关的能力。这些变化将被预测为干扰类似LTP的事件以及学习和记忆。因此，在这项建议中，我们希望确定CASK和CaMKII活性在利用苍蝇进行学习和记忆的突触可塑性中的直接作用。为了实现这一点，我们将创造新的苍蝇CaMKII和CASK突变体，并确定这些突变体一起或单独对苍蝇大脑中参与学习和记忆的部分的一系列突触事件的影响。最后，我们将确定CaMKII和CASK在果蝇学习和记忆行为中的作用。这将为了解大脑如何进化其获取和存储信息的巨大能力提供重要的见解。

The aim of this proposal is to better understand the molecular mechanisms by which memories are formed in the brain. Research into memory is particularly important as it gives us our sense of identity. Deficits in learning and memory occur in many diseases, injuries and during aging. Identifying the key molecules involved in these processes, will help reveal targets for new therapeutic interventions to reverse the devastating consequences of memory loss, this research is particularly important for our aging population. The brain consists of many cells or neurons that communicate via connections called synapses. Information flows through neurons via small electrical impulses, a bit like a computer. At most synapses these electrical impulses cause release of chemicals that bind to the output neuron causing it to become more excitable and propagate the electrical impulse to the next neuron in the circuit. The brain also stores information during learning and retrieves it as memory. There are special parts of the brain for learning e.g. the hippocampus. When an animal experiences learning stimuli there is a persistent increase in synaptic transmission between hippocampal neurons called Long Term Potentiation (LTP), this increase continues after the original stimulus is removed and is a synaptic mechanism for learning. These long-term changes in synaptic activity can cause increases in synaptic growth and connections between neurons, a process called synaptic plasticity that is thought to be a synaptic mechanism of memory. LTP and learning is initiated by calcium (Ca2+) entering the neuron and activating an enzyme called Ca2+ responsive kinase (CaMKII). CaMKII is abundant in the brain, constituting 1-2% of its total protein and is one of the main synaptic proteins. Once activated by increased Ca2+, CaMKII is able to cause a switch in its own activity so that it remains active even after Ca2+ has gone down. This special ability of CaMKII to maintain its own activity has been termed 'the molecular memory switch' and is required for both LTP and learning. CaMKII then regulates the activity of other proteins at the synapse that together maintain the increased synaptic transmission of LTP. In addition CaMKII activity can lead to many of the other changes occurring during synaptic plasticity and memory formation. These CaMKII mediated changes in synaptic plasticity are required for learning and memory in most animals including Drosophila. Although fruitflies are small they are smart, for instance they can land on the ceiling and detect that fruit in your fruit bowl has gone off before you can. In this proposal we wish to study CaMKII-mediated synaptic mechanisms of learning and memory further taking advantage of powerful genetics of Drosophila. One important question we wish to answer is: How is CaMKII's activity regulated and localised at synapses during learning? We have found that in flies like in mammals, at inactive synapses with low levels of Ca2+, CaMKII can regulate its own activity by a second mechanism that tends to inactivate CaMKII. We found a novel protein that interacts with CaMKII at fly synapses called CASK that tends to inactivate CaMKII thereby disrupting the ability of CaMKII to undergo the molecular memory switch. These changes would be predicted to interfere with LTP-like events and learning and memory. Therefore in this proposal we wish to determine the direct role of CASK and CaMKII activity in synaptic plasticity underlying learning and memory using flies. To achieve this we will make new fly CaMKII and CASK mutants and determine the effect of these together or alone on a range of synaptic events in parts of the fly brain that mediate learning and memory. Finally we will determine the role of CaMKII and CASK in the fly's learning and memory behaviour. This will provide important insight into how brains have evolved their huge capacity to acquire and store information.