Fluegel Megan L, Parker Tracey J, Pallanck Leo J
Molecular and Cellular Biology Graduate Program, University of Washington, Seattle, Washington 98195, USA.
Genetics. 2006 Jan;172(1):185-96. doi: 10.1534/genetics.105.046565. Epub 2005 Aug 3.
The molecular mechanisms by which dietary cholesterol is trafficked within cells are poorly understood. Previous work indicates that the NPC1 family of proteins plays an important role in this process, although the precise functions performed by this protein family remain elusive. We have taken a genetic approach to further explore the NPC1 family in the fruit fly Drosophila melanogaster. The Drosophila genome encodes two NPC1 homologs, designated NPC1a and NPC1b, that exhibit 42% and 35% identity to the human NPC1 protein, respectively. Here we describe the results of mutational analysis of the NPC1a gene. The NPC1a gene is ubiquitously expressed, and a null allele of NPC1a confers early larval lethality. The recessive lethal phenotype of NPC1a mutants can be partially rescued on a diet of high cholesterol or one that includes the insect steroid hormone 20-hydroxyecdysone. We also find that expression of NPC1a in the ring gland is sufficient to rescue the lethality associated with the loss of NPC1a and that cholesterol levels in NPC1a mutant larvae are unchanged relative to controls. Our results suggest that NPC1a promotes efficient intracellular trafficking of sterols in many Drosophila tissues including the ring gland where sterols must be delivered to sites of ecdysone synthesis.
饮食中的胆固醇在细胞内运输的分子机制目前还知之甚少。先前的研究表明，NPC1蛋白家族在这一过程中发挥着重要作用，尽管该蛋白家族的确切功能仍不清楚。我们采用遗传学方法，在果蝇中进一步探究NPC1家族。果蝇基因组编码两个NPC1同源物，分别命名为NPC1a和NPC1b，它们与人类NPC1蛋白的同源性分别为42%和35%。在此，我们描述了NPC1a基因突变分析的结果。NPC1a基因在全身广泛表达，NPC1a的无效等位基因会导致幼虫早期死亡。NPC1a突变体的隐性致死表型在高胆固醇饮食或含有昆虫类固醇激素20-羟基蜕皮酮的饮食中可得到部分挽救。我们还发现，在环腺中表达NPC1a足以挽救因NPC1a缺失而导致的致死性，并且NPC1a突变体幼虫中的胆固醇水平相对于对照组没有变化。我们的结果表明，NPC1a促进了固醇在包括环腺在内的许多果蝇组织中的高效细胞内运输，在环腺中，固醇必须被输送到蜕皮激素合成的部位。
