In Caenorhabditis elegans, the cha-1 gene encodes choline acetyltransferase (ChAT), the enzyme that synthesizes the neurotransmitter acetylcholine. We have analyzed a large number of cha-1 hypomorphic mutants, most of which are missense alleles. Some homozygous cha-1 mutants have approximately normal ChAT immunoreactivity; many other alleles lead to consistent reductions in synaptic immunostaining, although the residual protein appears to be stable. Regardless of protein levels, neuromuscular function of almost all mutants is temperature sensitive, i.e., neuromuscular function is worse at 25° than at 14°. We show that the temperature effects are not related to acetylcholine release, but specifically to alterations in acetylcholine synthesis. This is not a temperature-dependent developmental phenotype, because animals raised at 20° to young adulthood and then shifted for 2 hours to either 14° or 25° had swimming and pharyngeal pumping rates similar to animals grown and assayed at either 14° or 25°, respectively. We also show that the temperature-sensitive phenotypes are not limited to missense alleles; rather, they are a property of most or all severe cha-1 hypomorphs. We suggest that our data are consistent with a model of ChAT protein physically, but not covalently, associated with synaptic vesicles; and there is a temperature-dependent equilibrium between vesicle-associated and cytoplasmic (i.e., soluble) ChAT. Presumably, in severe cha-1 hypomorphs, increasing the temperature would promote dissociation of some of the mutant ChAT protein from synaptic vesicles, thus removing the site of acetylcholine synthesis (ChAT) from the site of vesicular acetylcholine transport. This, in turn, would decrease the rate and extent of vesicle-filling, thus increasing the severity of the behavioral deficits.

中文翻译：

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对秀丽隐杆线虫乙酰胆碱合成突变体的分析揭示了对胆碱能神经肌肉功能的温度敏感要求。

在秀丽隐杆线虫中，cha-1 基因编码胆碱乙酰转移酶 (ChAT)，该酶可合成神经递质乙酰胆碱。我们分析了大量的 cha-1 亚型突变体，其中大部分是错义等位基因。一些纯合 cha-1 突变体具有大致正常的 ChAT 免疫反应性；许多其他等位基因导致突触免疫染色持续减少，尽管残留的蛋白质似乎是稳定的。无论蛋白质水平如何，几乎所有突变体的神经肌肉功能都对温度敏感，即，25°时的神经肌肉功能比14°时差。我们表明温度效应与乙酰胆碱的释放无关，而与乙酰胆碱合成的变化有关。这不是温度依赖性发育表型，因为在 20° 到成年后饲养的动物，然后在 2 小时内转移到 14° 或 25°，其游泳和咽部泵送速率与分别在 14° 或 25° 生长和测定的动物相似。我们还表明，温度敏感表型不仅限于错义等位基因；相反，它们是大多数或所有严重 cha-1 亚型的属性。我们建议我们的数据与与突触小泡相关的物理上的 ChAT 蛋白模型一致，但不是共价的；并且在囊泡相关和细胞质（即可溶性）ChAT 之间存在温度依赖性平衡。据推测，在严重的 cha-1 亚型中，升高温度会促进一些突变的 ChAT 蛋白从突触小泡中解离，从而从囊泡乙酰胆碱转运位点去除乙酰胆碱合成位点 (ChAT)。这反过来会降低囊泡填充的速度和程度，从而增加行为缺陷的严重程度。