Department of Human Genetics, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, California, United States of America.
PLoS One. 2013 Sep 6;8(9):e71664. doi: 10.1371/journal.pone.0071664. eCollection 2013.
In Drosophila, RNAi targeting of either dGyk or dGK can result in two alternative phenotypes: adult glycerol hypersensitivity or larval lethality. Here we compare these two phenotypes at the level of glycerol kinase (GK) phosphorylation activity, dGyk and dGK-RNA expression, and glycerol levels. We found both phenotypes exhibit reduced but similar levels of GK phosphorylation activity. Reduced RNA expression levels of dGyk and dGK corresponded with RNAi progeny that developed into glycerol hypersensitive adult flies. However, quantification of dGyk/dGK expression levels for the larval lethality phenotype revealed unexpected levels possibly due to a compensatory mechanism between dGyk and dGK or RNAi inhibition. The enzymatic role of glycerol kinase converts glycerol to glycerol 3-phosphate. As expected, elevated glycerol levels were observed in larvae that went on to develop into glycerol hypersensitive adults. Interestingly, larvae that died before eclosion revealed extremely low glycerol levels. Further characterization identified a wing phenotype that is enhanced by a dGpdh null mutation, indicating disrupted glycerol metabolism underlies the wing phenotype. In humans, glycerol kinase deficiency (GKD) exhibits a wide range of phenotypic variation with no obvious genotype-phenotype correlations. Additionally, disease severity often does not correlate with GK phosphorylation activity. It is intriguing that both human GKD patients and our GKD Drosophila model show a range of phenotype severity. Additionally, the lack of correlation between GK phosphorylation and dGyk/dGK-RNA expression with phenotypic severity suggests further study including understanding the alternative functions of the GK protein, could provide insights into the complex pathogenic mechanism observed in human GKD patients.
在果蝇中，靶向 dGyk 或 dGK 的 RNAi 可导致两种替代表型：成年甘油敏感性或幼虫致死性。在这里，我们在甘油激酶 (GK) 磷酸化活性、dGyk 和 dGK-RNA 表达和甘油水平方面比较了这两种表型。我们发现这两种表型都表现出降低但相似的 GK 磷酸化活性水平。dGyk 和 dGK 的 RNA 表达水平降低与发育成甘油敏感性成虫的 RNAi 后代相对应。然而，对于幼虫致死性表型的 dGyk/dGK 表达水平的定量分析显示出出乎意料的水平，可能是由于 dGyk 和 dGK 之间的补偿机制或 RNAi 抑制所致。甘油激酶的酶促作用将甘油转化为甘油 3-磷酸。正如预期的那样，在发育成甘油敏感性成虫的幼虫中观察到甘油水平升高。有趣的是，在羽化前死亡的幼虫表现出极低的甘油水平。进一步的特征鉴定确定了一种翅膀表型，该表型通过 dGpdh 缺失突变增强，表明甘油代谢紊乱是翅膀表型的基础。在人类中，甘油激酶缺乏症 (GKD) 表现出广泛的表型变异，没有明显的基因型-表型相关性。此外，疾病严重程度通常与 GK 磷酸化活性无关。有趣的是，人类 GKD 患者和我们的 GKD 果蝇模型都表现出一系列表型严重程度，这表明进一步的研究，包括了解 GK 蛋白的替代功能，可能为理解人类 GKD 患者中观察到的复杂发病机制提供深入了解。
