In multicellular organisms, glycosylation regulates various developmental signaling pathways including the Notch pathway. One of the O-linked glycans added to epidermal growth factor-like (EGF) repeats in animal proteins including the Notch receptors is the xylose–xylose–glucose-O oligosaccharide. Drosophila glucoside xylosyltransferase (Gxylt) Shams negatively regulates Notch signaling in specific contexts. Since Shams adds the first xylose residue to O-glucose, its loss-of-function phenotype could be due to the loss of the first xylose, the second xylose or both. To examine the contribution of the second xylose residues to Drosophila Notch signaling, we have performed biochemical and genetic analysis on CG11388, which is the Drosophila homolog of human xyloside xylosyltransferase 1 (XXYLT1). Experiments in S2 cells indicated that similar to human XXYLT1, CG11388 can add the second xylose to xylose–glucose-O glycans. Flies lacking both copies of CG11388 (Xxylt) are viable and fertile and do not show gross phenotypes indicative of altered Notch signaling. However, genetic interaction experiments show that in sensitized genetic backgrounds with decreased or increased Notch pathway components, loss of Xxylt promotes Delta-mediated activation of Notch. Unexpectedly, we find that in such sensitized backgrounds, even loss of one copy of the fly Gxylt shams enhances Delta-mediated Notch activation. Taken together, these data indicate that while the first xylose plays a key role in tuning the Delta-mediated Notch signaling in Drosophila, the second xylose has a fine-tuning role only revealed in sensitized genetic backgrounds.

中文翻译：

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敏感的遗传背景揭示了 EGF 重复木糖基转移酶在果蝇 Notch 信号传导中的不同作用


在多细胞生物中，糖基化调节各种发育信号通路，包括 Notch 通路。添加到包括 Notch 受体在内的动物蛋白中的表皮生长因子样 (EGF) 重复序列中的 O 连接聚糖之一是木糖-木糖-葡萄糖-O 寡糖。果蝇葡萄糖苷木糖基转移酶 (Gxylt) Shams 在特定情况下负向调节 Notch 信号传导。由于 Shams 将第一个木糖残基添加到 O-葡萄糖上，因此其功能丧失表型可能是由于第一个木糖、第二个木糖或两者的丢失所致。为了检查第二个木糖残基对果蝇 Notch 信号传导的贡献，我们对 CG11388 进行了生化和遗传分析，CG11388 是人木糖苷木糖基转移酶 1 (XXYLT1) 的果蝇同源物。 S2 细胞中的实验表明，与人 XXYLT1 类似，CG11388 可以将第二个木糖添加到木糖-葡萄糖-O 聚糖中。缺乏 CG11388 (Xxylt) 两个拷贝的果蝇是可存活且可繁殖的，并且不会显示出表明 Notch 信号改变的总体表型。然而，遗传相互作用实验表明，在 Notch 通路成分减少或增加的致敏遗传背景中，Xxylt 的缺失会促进 Delta 介导的 Notch 激活。出乎意料的是，我们发现在如此敏感的背景下，即使丢失一份果蝇 Gxylt 假冒副本也会增强 Delta 介导的 Notch 激活。总而言之，这些数据表明，虽然第一种木糖在调节果蝇中 Delta 介导的 Notch 信号传导中发挥关键作用，但第二种木糖仅在致敏遗传背景中具有微调作用。