Riederer B M, Barakat-Walter I
Institut d'Anatomie, Université de Lausanne, Faculté de Médecine, Switzerland.
Brain Res Dev Brain Res. 1992 Jul 24;68(1):111-23. doi: 10.1016/0165-3806(92)90253-s.
Microtubule-associated proteins (MAPs) are essential components necessary for the early growth process of axons and dendrites, and for the structural organization within cells. Both MAP2 and MAP5 are involved in these events, MAP2 occupying a role predominantly in dendrites, and MAP5 being involved in both axonal and dendritic growth. In the chick dorsal root ganglia, pseudo-unipolar sensory neurons have a T-shaped axon and are devoid of any dendrites. Therefore, they offer an ideal model to study the differential expression of MAPs during DRG development, specifically during axonal growth. In this study we have analyzed the expression and localization of MAP2 and MAP5 isoforms during chick dorsal root ganglia development in vivo, and in cell culture. In DRG, both MAPs appeared as early as E5. MAP2 consists of the 3 isoforms MAP2a, b and c. On blots, no MAP2a could be found at any stage. MAP2b increased between E6 and E10 and thereafter diminished slowly in concentration, while MAP2c was found between stages E6 and E10 in DRG. By immunocytochemistry, MAP2 isoforms were mainly located in the neuronal perikarya and in the proximal portion of axons, but could not be localized to distal axonal segments, nor in sciatic nerve at any developmental stage. On blots, MAP5 was present in two isoforms, MAP5a and MAP5b. The concentration of MAP5a was highest at E6 and then decreased to a low level at E18. In contrast, MAP5b increased between E6 and E10, and rapidly decreased after E14. Only MAP5a was present in sciatic nerve up to E14. Immunocytochemistry revealed that MAP5 was localized mainly in axons, although neuronal perikarya exhibited a faint immunostaining. Strong staining of axons was observed between E10 and E14, at a time coincidental to a period of intense axonal outgrowth. After E14 immunolabeling of MAP5 decreased abruptly. In DRG culture, MAP2 was found exclusively in the neuronal perikarya and the most proximal neurite segment. In contrast, MAP5 was detected in the neuronal cell bodies and all along their neurites. In conclusion, MAP2 seems involved in the early establishment of the cytoarchitecture of cell bodies and the proximal axon segment of somatosensory neurons, while MAP5 is clearly related to axonal growth.
微管相关蛋白（MAPs）是轴突和树突早期生长过程以及细胞内结构组织所必需的重要组成部分。MAP2和MAP5都参与了这些过程，MAP2主要在树突中发挥作用，而MAP5则参与轴突和树突的生长。在鸡背根神经节中，假单极感觉神经元有一个T形轴突，没有任何树突。因此，它们为研究背根神经节发育过程中，特别是轴突生长过程中MAPs的差异表达提供了一个理想模型。在本研究中，我们分析了MAP2和MAP5亚型在鸡背根神经节体内发育和细胞培养过程中的表达和定位。在背根神经节中，两种MAPs早在胚胎第5天（E5）就出现了。MAP2由MAP2a、b和c三种亚型组成。在印迹分析中，在任何阶段都未发现MAP2a。MAP2b在E6到E10之间增加，此后浓度缓慢下降，而MAP2c在背根神经节的E6到E10阶段被发现。通过免疫细胞化学方法，MAP2亚型主要位于神经元胞体和轴突的近端部分，但在任何发育阶段都不能定位到轴突的远端部分，也不能在坐骨神经中定位。在印迹分析中，MAP5以MAP5a和MAP5b两种亚型存在。MAP5a的浓度在E6时最高，然后在E18时降至低水平。相反，MAP5b在E6到E10之间增加，并在E14后迅速下降。直到E14，坐骨神经中只存在MAP5a。免疫细胞化学显示，MAP5主要定位于轴突，尽管神经元胞体呈现出微弱的免疫染色。在E10到E14之间观察到轴突有强烈染色，这与轴突大量生长的时期一致。E14后，MAP5的免疫标记突然下降。在背根神经节培养物中，MAP2仅在神经元胞体和最近端的神经突段中发现。相反，MAP5在神经元细胞体及其所有神经突中都能检测到。总之，MAP2似乎参与了体感神经元细胞体和近端轴突段细胞结构的早期建立，而MAP5显然与轴突生长有关。
