Multiple fates of newly synthesized neurofilament proteins: evidence for a stationary neurofilament network distributed nonuniformly along axons of retinal ganglion cell neurons.
Multiple fates of newly synthesized neurofilament proteins: evidence for a stationary neurofilament network distributed nonuniformly along axons of retinal ganglion cell neurons.
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DOI：
10.1083/jcb.102.2.647
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发表时间：
1986-02
期刊：
影响因子：
--
通讯作者：
Logvinenko KB
中科院分区：
文献类型：
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作者：
Nixon RA;Logvinenko KB
我们研究了神经丝蛋白(NFP)合成后1~180d在小鼠视网膜神经节细胞(RGC)神经元中的去向，并检测了新合成的70、140和200 kD亚基沿RGC轴突的近端到远端的分布与神经丝的分布。改进的玻璃体内注射[~3H]Pro的方法使我们能够量化注射后不同时间内放射性标记NFP亚单位积累和随后下降的变化，并首次估计轴突内不同池中NFP的稳态水平。根据从视神经和视束组成的9 mm“轴突窗口”消失的动力学以及它们沿轴突的时空分布模式，区分了两个新合成的三联体NFP池。第一池在注射后17~45d呈指数级消失，半衰期为20d，其标记波前沿轴突以0.5~0.7 mm/d的速度前进，17d到达轴突窗口的远端，表明这种丢失代表了构成轴浆运输最慢时相的神经丝蛋白从轴突退出。然而，45d后，约32%的放射性标记神经丝蛋白仍留在轴突中，并以更慢的速度指数消失(t1/2=55d)。这第二个NFP池假定沿着轴突的不均匀分布，其特征是近端和远端的放射活性增加了2.5倍的梯度。从45d到180d，这种分布模式没有改变，表明第二池中的神经丝蛋白在轴突中构成了一个相对稳定的结构。根据轴突中每个神经丝池的相对放射性和停留时间(或周转)，我们估计，在稳定状态下，小鼠RGC轴突中可能有更多的神经丝蛋白处于静止状态，而不是经历持续缓慢的轴浆运输。这一结论得到了总NFP含量的生化分析和RGC轴突上神经丝分布的电子显微镜形态计量学研究的支持。70 kD、140 kD和200 kD的亚基显示出2.5倍的近端和远端沿RGC轴突含量增加的梯度。神经细丝在远端轴突水平更多，与NFP含量的增加平行。
We have studied the fate of neurofilament proteins (NFPs) in mouse retinal ganglion cell (RGC) neurons from 1 to 180 d after synthesis and examined the proximal-to-distal distribution of the newly synthesized 70-, 140-, and 200-kD subunits along RGC axons relative to the distribution of neurofilaments. Improved methodology for intravitreal delivery of [3H]proline enabled us to quantitate changes in the accumulation and subsequent decline of radiolabeled NFP subunits at various postinjection intervals and, for the first time, to estimate the steady state levels of NFPs in different pools within axons. Two pools of newly synthesized triplet NFPs were distinguished based on their kinetics of disappearance from a 9-mm "axonal window" comprising the optic nerve and tract and their temporal-spatial distribution pattern along axons. The first pool disappeared exponentially between 17 and 45 d after injection with a half-life of 20 d. Its radiolabeled wavefront advanced along axons at 0.5-0.7 mm/d before reaching the distal end of the axonal window at 17 d, indicating that this loss represented the exit of neurofilament proteins composing the slowest phase of axoplasmic transport (SCa or group V) from axons. About 32% of the total pool of radiolabeled neurofilament proteins, however, remained in axons after 45 d and disappeared exponentially at a much slower rate (t 1/2 = 55 d). This second NFP pool assumed a nonuniform distribution along axons that was characterized proximally to distally by a 2.5-fold gradient of increasing radioactivity. This distribution pattern did not change between 45 and 180 d indicating that neurofilament proteins in the second pool constitute a relatively stationary structure in axons. Based on the relative radioactivities and residence time (or turnover) of each neurofilament pool in axons, we estimate that, in the steady state, more neurofilament proteins in mouse RGC axons may be stationary than are undergoing continuous slow axoplasmic transport. This conclusion was supported by biochemical analyses of total NFP content and by electron microscopic morphometric studies of neurofilament distribution along RGC axons. The 70-, 140-, and 200-kD subunits displayed a 2.5-fold proximal to distal gradient of increasing content along RGC axons. Neurofilaments were more numerous at distal axonal levels, paralleling the increased content of NFP.(ABSTRACT TRUNCATED AT 400 WORDS)