Tai Mei-Hui, Zipser Birgit
Department of Pediatrics and Human Development, Michigan State University, East Lansing, MI 48824, USA.
J Neurocytol. 2002 Sep-Nov;31(8-9):743-54. doi: 10.1023/a:1025756015281.
Differences in carbohydrate signaling control sequential steps in synaptic growth of sensory afferents in the leech. The relevant glycans are constitutive and developmentally regulated modifications of leechCAM and Tractin (family members of NCAM and L1) that are specific to the surface of sensory afferents. A mannosidic glycosylation mediates the dynamic growth of early afferents as they explore their target region through sprouting sensory arbors rich with synaptic vesicles. Later emerging galactosidic glycosylations serve as markers for subsets of the same sensory afferents that correlate with different sensory modalities. These developmentally regulated galactose markers now oppose the function of the constitutive mannose marker. Sensory afferents gain cell-cell contact with central neurons and self-similar afferents, but lose filopodia and synaptic vesicles. Extant vesicles are confined to sites of en passant synapse formation. The transformation of sensory afferent growth, progressing from mannose- to galactose-specific recognition, is consistent with a change from cell-matrix to cell-cell contact. While the constitutive mannosidic glycosylation promotes dynamic growth, developmentally regulated galactosidic glycosylations of the same cell adhesion molecules promote tissue stability. The persistence of both types of neutral glycans beyond embryonic age allows their function in synaptic plasticity during habituation and learning.
碳水化合物信号的差异控制着水蛭感觉传入神经突触生长的连续步骤。相关聚糖是水蛭细胞粘附分子（leechCAM）和束状蛋白（Tractin，分别为神经细胞粘附分子（NCAM）和L1的家族成员）的组成性且受发育调控的修饰，这些修饰对感觉传入神经表面具有特异性。一种甘露糖苷糖基化介导早期传入神经的动态生长，此时它们通过富含突触小泡的发芽感觉树突探索其靶区域。后来出现的半乳糖苷糖基化作为同一感觉传入神经亚群的标记，与不同的感觉模式相关。这些受发育调控的半乳糖标记现在与组成性甘露糖标记的功能相反。感觉传入神经与中枢神经元和自身相似的传入神经建立细胞间接触，但失去丝状伪足和突触小泡。现存的小泡局限于过路突触形成的部位。感觉传入神经生长从甘露糖特异性识别向半乳糖特异性识别的转变，与从细胞 - 基质接触到细胞 - 细胞接触的变化一致。虽然组成性甘露糖苷糖基化促进动态生长，但同一细胞粘附分子的受发育调控的半乳糖苷糖基化促进组织稳定性。这两种中性聚糖在胚胎期之后的持续存在使其在习惯化和学习过程中的突触可塑性中发挥作用。
