Takahashi H
Department of Anatomy, Hirosaki University School of Medicine, Japan.
Anat Embryol (Berl). 1992;185(4):389-400. doi: 10.1007/BF00188550.
The masking effect of sialic acid on cell surface carbohydrates localized on the ectoderm in stage 6-11 bantam embryos was examined using fluorescein isothiocyanate-labeled Con A, PNA, SBA, LFA, and LPA before and after neuraminidase treatment. The results showed selective lectin binding on both the neuroectoderm and the surface ectoderm. In general, these lectin-binding sites increased or were at least expressed on neuroectoderm during neurulation. On the apical surfaces of the developing neuroectoderm, masked Con A-binding sites were evident from the earliest stage and rapidly increased. These sites coexisted with unmasked binding sites which gradually increased. Masked PNA sites were rarely observed but became abundant in later stages, even though coexistent unmasked sites also rapidly increased. Masked SBA sites were poorly observable in the early stage and gradually increased thereafter, whereas unmasked sites were expressed at later stages. On the basal surfaces masked Con A sites were evident in the early stages but gradually decreased in later stages, whereas unmasked sites were relatively abundant and increased thereafter. Masked PNA sites were evident and increased very rapidly, whereas unmasked sites became observable up to the latest stage. Masked SBA sites were minimal in all three stages, and unmasked sites expressed themselves slightly at later stages. The change in composition of carbohydrates on the developing neuroectoderm was obviously different from that on the developing surface ectoderm. On the contact surface of the neural ridge, the number of masked sites of penultimate sugars was large at Con A sites, slight at PNA and SBA sites, which coexisted with unmasked sugar chain terminals in the areas where Con A sites were moderate and where PNA and SBA sites were poor. Finally, the role of masking on binding sites for Con A, PNA and SBA during neural tube closure is discussed, and the observation that the apparent masking effect on three lectin binding sites did not correspond to the content of sialic acid detected by LFA and LPA is a subject for further study.
使用异硫氰酸荧光素标记的刀豆球蛋白A（Con A）、花生凝集素（PNA）、大豆凝集素（SBA）、荆豆凝集素（LFA）和小扁豆凝集素（LPA），在神经氨酸酶处理前后，检测了6-11期矮脚鸡胚胎中外胚层上唾液酸对细胞表面碳水化合物的掩盖作用。结果显示，在神经外胚层和表面外胚层上均有选择性凝集素结合。一般来说，在神经胚形成过程中，这些凝集素结合位点在神经外胚层上增加或至少表达。在发育中的神经外胚层的顶端表面，最早阶段就明显存在被掩盖的Con A结合位点，且迅速增加。这些位点与逐渐增加的未被掩盖的结合位点共存。很少观察到被掩盖的PNA位点，但在后期变得丰富，尽管共存的未被掩盖的位点也迅速增加。被掩盖的SBA位点在早期难以观察到，此后逐渐增加，而未被掩盖的位点在后期表达。在基底表面，被掩盖的Con A位点在早期明显，但在后期逐渐减少，而未被掩盖的位点相对丰富并在此后增加。被掩盖的PNA位点明显且增加非常迅速，而未被掩盖的位点直到最晚阶段才变得可观察到。被掩盖的SBA位点在所有三个阶段都很少，未被掩盖的位点在后期略有表达。发育中的神经外胚层上碳水化合物组成的变化明显不同于发育中的表面外胚层。在神经嵴的接触表面，倒数第二个糖的被掩盖位点在Con A位点数量较多，在PNA和SBA位点较少，在Con A位点适中且PNA和SBA位点较少的区域与未被掩盖的糖链末端共存。最后，讨论了在神经管闭合过程中掩盖对Con A、PNA和SBA结合位点的作用，并且关于对三种凝集素结合位点的明显掩盖效应与LFA和LPA检测到的唾液酸含量不相符这一观察结果是进一步研究的课题。
