C. elegans as a model to study the role of SM proteins in neurotransmitter release in vivo

细胞之间的交流通过化学信使如激素和神经递质进行。这些化学信使中的许多通常储存在细胞内的膜封闭囊泡中，并且只能通过这些囊泡与细胞膜的融合在称为胞吐的过程中释放。肉毒杆菌中毒导致的致命性瘫痪说明了这一机制的重要性，肉毒杆菌中毒通过阻断神经细胞分泌神经递质来起作用。胞吐作用究竟是如何发生的一直是个谜，直到最近十年，一组类似的蛋白质--“陷阱蛋白”--在所有细胞中控制着这一过程。据信SNARE蛋白在胞吐期间直接驱动膜融合，但其他神经细胞蛋白调节SNARE的活性，从而实现对神经递质释放的复杂控制。哺乳动物中一种这样的调节蛋白的良好候选者是Munc 18。事实上，Munc 18紧密结合SNARE蛋白，突触融合蛋白，是体内神经递质释放所必需的。munc 18是以一种名为unc-18的类似蛋白质命名的，这种蛋白质是多年前在蠕虫中发现的。像哺乳动物蛋白一样，unc-18与突触融合蛋白结合，对体内神经传递很重要。因此，unc-18/Munc 18在神经细胞中的关键功能可能涉及与突触融合蛋白的结合。然而，Munc 18也与不同的神经细胞蛋白结合，因此尚不清楚哪些相互作用对胞吐作用最重要。此外，Munc 18影响胞吐过程的多个阶段，其中一些似乎不需要突触融合蛋白结合。我们的目标是通过设计unc-18的突变体来阐明这个问题，这些突变体可以与unc-18的一些结合伴侣结合，而不是其他结合伴侣。对神经细胞中含有这些突变蛋白的蠕虫进行分析，将确定哪些unc-18相互作用对胞吐作用是重要的。由于这些突变体也会改变神经细胞释放的神经递质的数量，我们将研究这如何影响活体动物的行为。由于正在研究的蛋白质与我们自己的神经细胞中的蛋白质相似，这项研究的结果将阐明人脑功能的分子基础。

Communication between cells occurs via chemical messengers such as hormones and neurotransmitters. Many of these chemical messengers are normally stored in membrane-enclosed vesicles inside cells and can only be released by fusion of these vesicles with the cell membrane in the process known as exocytosis. The importance of this mechanism is illustrated by the fatal paralysis caused by botulism, which works by blocking the exocytosis of neurotransmitter from nerve cells. Exactly how exocytosis occurs was mysterious until the last decade, when it emerged that a set of similar proteins - the 'SNARE proteins' - controlled this process in all cells. The SNARE proteins are believed to directly drive membrane fusion during exocytosis, but other nerve cell proteins regulate the activity of the SNAREs, enabling sophisticated control of neurotransmitter release. A good candidate for one such regulatory protein in mammals is Munc18. Indeed, Munc18 binds tightly to the SNARE protein, syntaxin, and is essential for neurotransmitter release in vivo. Munc18 was named after a similar protein called unc-18 that was discovered years earlier in worms. Like the mammalian protein, unc-18 binds to syntaxin and is important for neurotransmission in vivo. It therefore seems likely that the critical function of unc-18/Munc18 in nerve cells involves binding to syntaxin. However, Munc18 also binds to different nerve cell proteins, so it is not clear which interactions are most important for exocytosis. Furthermore, Munc18 affects multiple stages of the exocytosis process and some of these do not appear to require syntaxin binding. We aim to shed light on this issue by engineering mutant versions of unc-18 that bind to some binding partners of unc-18, but not others. Analysis of worms containing these mutant proteins in nerve cells will identify which unc-18 interactions are important for exocytosis. As these mutants should also change the amount of neurotransmitter released from nerve cells, we will study how this contributes to behaviour in the living animal. As the proteins being studied are similar to those in our own nerve cells, the results of this study will illuminate the molecular basis of human brain function.