Abstract

Among the enzymes of the biosynthesis of sialoglycoconjugates, UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE), catalyzing the first essential step of the sialic acid (Sia) de novo biosynthesis, and CMP-Sia synthase (CMAS), activating Sia to CMP-Sia, are particularly important. The knockout of either of these enzymes in mice is embryonically lethal. While the lethality of Cmas−/− mice has been attributed to a maternal complement attack against asialo fetal placental cells, the cause of lethality in Gne-deficient embryos has remained elusive. Here, we advanced the significance of sialylation for embryonic development through detailed histological analyses of Gne−/− embryos and placentae. We found that Gne−/− embryonic and extraembryonic tissues are hyposialylated, rather than completely deficient of sialoglycans which holds true for Cmas−/− embryos. Residual sialylation of Gne−/− cells can be explained by scavenging free Sia from sialylated maternal serum glycoconjugates via the lysosomal salvage pathway. The placental architecture of Gne−/− mice was unaffected, but severe hemorrhages in the neuroepithelium with extensive bleeding into the cephalic ventricles were present at E12.5 in the mutants. At E13.5, the vast majority of Gne−/− embryos were asystolic. This phenotype persisted when Gne−/− mice were backcrossed to a complement component 3-deficient background, confirming distinct pathomechanisms of Cmas−/− and Gne−/− mice. We conclude that the low level of sialylation observed in Gne−/− mice is sufficient, both for immune homeostasis at the fetal-maternal interface and for embryonic development until E12.5. However, formation of the neural microvasculature is the first critical process depending on a higher degree of sialylation during development of the embryo proper.

中文翻译：

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小鼠基因缺失导致胚胎发育过程中致命的脑出血

摘要

在唾液酸糖缀合物生物合成的酶中，UDP- N-乙酰葡糖胺-2-差向异构酶/ N-乙酰甘露糖胺激酶 (GNE)，催化唾液酸 (Sia)从头生物合成的第一个重要步骤，以及 CMP-Sia 合酶 (CMAS )，将 Sia 激活为 CMP-Sia，尤为重要。在小鼠中敲除这些酶中的任何一种在胚胎上都是致命的。虽然Cmas-/-小鼠的致死性归因于母体补体对去唾液酸胎儿胎盘细胞的攻击，但Gne缺陷胚胎致死性的原因仍然难以捉摸。在这里，我们通过对Gne-/-的详细组织学分析，提高了唾液酸化对胚胎发育的意义。胚胎和胎盘。我们发现Gne-/-胚胎和胚胎外组织是低唾液酸化的，而不是完全缺乏对Cmas-/-胚胎适用的唾液聚糖。Gne-/-细胞的残留唾液酸化可以通过溶酶体补救途径从唾液酸化母体血清糖缀合物中清除游离 Sia 来解释。Gne-/-小鼠的胎盘结构不受影响，但突变体的 E12.5 处出现神经上皮严重出血，头脑室大量出血。在 E13.5，绝大多数Gne-/-胚胎是无收缩的。当Gne-/-时，这种表型持续存在小鼠与补体成分 3 缺陷背景回交，证实了Cmas-/-和Gne-/-小鼠的不同病理机制。我们得出结论，在Gne-/-小鼠中观察到的低水平唾液酸化是足够的，这对于胎儿-母体界面的免疫稳态和胚胎发育直到 E12.5 都是足够的。然而，神经微脉管系统的形成是第一个关键过程，这取决于胚胎发育过程中更高程度的唾液酸化。