Kalil K, Perdew M
Department of Anatomy, University of Wisconsin, Madison 53706.
J Neurosci. 1988 Dec;8(12):4797-808. doi: 10.1523/JNEUROSCI.08-12-04797.1988.
The regulation of axon outgrowth is not well understood. In previous studies, however, axon elongation has been well correlated with expression of a small number of growth-associated proteins (GAPs). To identify other proteins whose expression could be correlated with axon outgrowth during development of CNS pathways, monoclonal antibodies were raised against growth cone particles isolated from neonatal hamster brains. Two of these antibodies recognized a brain-specific 33 kDa protein associated with intracellular membranes of axons and growth cones. Immunoblotting demonstrated a sharp developmental decline in levels of the protein in hamster brain during the first postnatal week and a more gradual decline thereafter. Immunocytochemical studies with the antibodies revealed ubiquitous staining of the neuropil during the first several days, which by the end of the first week became restricted to a few later-maturing pathways. Staining was most intense in the pyramidal tract and was well correlated with axon outgrowth, which continues until 14 d in this pathway. These results suggest that the 33 kDa protein may, like previously identified GAPs, play a role in axon elongation. Late outgrowth of the hamster pyramidal tract is also correlated with expression of another developmentally regulated protein, the high-molecular-weight neurofilament subunit (NF-H). Immunostaining with a monoclonal antibody that recognized phosphorylated NF-H demonstrated that this subunit does not begin to appear in the late-maturing pyramidal tract fibers until several weeks after birth, in striking contrast to intense immunoreactivity of other spinal cord pathways from postnatal day 1. This finding suggests that specific pathways may have a highly idiosyncratic time course for expression of neurofilament subunits.
轴突生长的调控机制尚未完全明确。然而，在先前的研究中，轴突伸长与少数生长相关蛋白（GAPs）的表达密切相关。为了确定在中枢神经系统通路发育过程中其表达可能与轴突生长相关的其他蛋白质，制备了针对从新生仓鼠脑部分离的生长锥颗粒的单克隆抗体。其中两种抗体识别一种与轴突和生长锥的细胞内膜相关的脑特异性33 kDa蛋白。免疫印迹显示，该蛋白在仓鼠脑内出生后第一周水平急剧下降，此后逐渐下降。用这些抗体进行的免疫细胞化学研究显示，在最初几天神经毡普遍染色，到第一周结束时，染色局限于一些较晚成熟的通路。在锥体束中染色最为强烈，且与轴突生长密切相关，该通路的轴突生长一直持续到14天。这些结果表明，33 kDa蛋白可能像先前鉴定的GAPs一样，在轴突伸长中发挥作用。仓鼠锥体束的晚期生长也与另一种受发育调控的蛋白——高分子量神经丝亚基（NF-H）的表达相关。用识别磷酸化NF-H的单克隆抗体进行免疫染色表明，该亚基直到出生后几周才开始出现在较晚成熟的锥体束纤维中，这与出生后第1天其他脊髓通路的强烈免疫反应形成鲜明对比。这一发现表明，特定通路在神经丝亚基表达方面可能具有高度独特的时间进程。
