Laboratory for Molecular Membrane Neuroscience, Brain Science Institute, RIKEN, Wako-Shi, Saitama, Japan.
Glia. 2010 Aug;58(10):1197-207. doi: 10.1002/glia.20999.
Glycosphingolipids (GSLs) occur in all mammalian plasma membranes. They are most abundant in neuronal cells and have essential roles in brain development. Glucosylceramide (GlcCer) synthase, which is encoded by the Ugcg gene, is the key enzyme driving the synthesis of most neuronal GSLs. Experiments using conditional Nestin-Cre Ugcg knockout mice have shown that GSL synthesis in vivo is essential, especially for brain maturation. However, the roles of GSL synthesis in mature neurons remain elusive, since Nestin-Cre is expressed in neural precursors as well as in postmitotic neurons. To address this problem, we generated Purkinje cell-specific Ugcg knockout mice using mice that express Cre under the control of the L7 promoter. In these mice, Purkinje cells survived for at least 10-18 weeks after Ugcg deletion. We observed apparent axonal degeneration characterized by the accumulation of axonal transport cargos and aberrant membrane structures. Dendrites, however, were not affected. In addition, loss of GSLs disrupted myelin sheaths, which were characterized by detached paranodal loops. Notably, we observed doubly myelinated axons enveloped by an additional concentric myelin sheath around the original sheath. Our data show that axonal GlcCer-based GSLs are essential for axonal homeostasis and correct myelin sheath formation.
糖鞘脂（Glycosphingolipids，GSLs）存在于所有哺乳动物的质膜中。它们在神经元细胞中含量最丰富，在大脑发育中具有重要作用。糖基神经酰胺（Glucosylceramide，GlcCer）合酶由 Ugcg 基因编码，是驱动大多数神经元 GSL 合成的关键酶。使用条件性巢蛋白启动子-Cre Ugcg 敲除小鼠的实验表明，体内 GSL 合成是必不可少的，特别是对大脑成熟而言。然而，GSL 合成在成熟神经元中的作用仍不清楚，因为巢蛋白启动子-Cre 在神经前体细胞和有丝分裂后神经元中均有表达。为了解决这个问题，我们使用 L7 启动子控制 Cre 表达的小鼠，生成了浦肯野细胞特异性 Ugcg 敲除小鼠。在这些小鼠中，Ugcg 缺失后浦肯野细胞至少存活了 10-18 周。我们观察到明显的轴突退化，其特征是轴突运输货物的积累和异常的膜结构。然而，树突没有受到影响。此外，GSL 的缺失破坏了髓鞘，其特征是分离的结旁环。值得注意的是，我们观察到双髓鞘轴突被原始髓鞘周围的另一个同心髓鞘包裹。我们的数据表明，轴突上的基于 GlcCer 的 GSLs 对于轴突的内稳态和正确的髓鞘形成是必不可少的。
