Kleiman R, Banker G, Steward O
Department of Neuroscience, University of Virginia Health Sciences Center, Charlottesville 22908.
J Neurosci. 1994 Mar;14(3 Pt 1):1130-40. doi: 10.1523/JNEUROSCI.14-03-01130.1994.
Neurons possess an RNA transport system that is present in dendrites (but not axons) and sort mRNAs so that some mRNAs are restricted to cell bodies while a few others (like the mRNA for MAP2) are present in dendrites. The present study evaluates when dendrite-specific RNA transport and mRNA sorting into cell body and somatodendritic compartments first appear in developing hippocampal neurons maintained in culture. A 3H-uridine pulse-chase paradigm was used to evaluate transport of newly synthesized RNA from the site of synthesis in the nucleus into the developing neurites. The intracellular distribution of mRNAs encoding actin, tubulin, GAP-43, and MAP2 as well as polyA RNA and rRNA was evaluated by in situ hybridization at different stages of development. Newly synthesized RNA was translocated into both developing axons and dendrites early in development, but only into dendrites as the neurons matured. Tubulin, GAP-43, and actin mRNAs, which are restricted to cell bodies in mature neurons, were found exclusively in neuronal cell bodies at all developmental stages. MAP2 mRNA, which is present in the dendrites of mature neurons, was present at very low levels in neurons at 2 or 3 d in culture and was not detectable within dendrites. The overall levels of MAP2 mRNA increased over time, and by 5-7 d in culture, MAP2 mRNA was detectable in some dendrites. PolyA RNA and rRNA were detectable in developing neurites including axons. Levels of polyA and rRNA increased in dendrites as neurons matured while labeling of axons diminished. By 10 d in culture, axonal labeling for polyA and rRNA had virtually disappeared. The increase in the levels of polyA, rRNA, and MAP2 mRNA in dendrites between 5 and 7 d in culture corresponds roughly with the appearance of other dendritic characteristics and the beginning of dendritic outgrowth.
神经元拥有一种RNA转运系统，该系统存在于树突中（而非轴突中），并对mRNA进行分类，使得一些mRNA局限于细胞体，而其他一些（如MAP2的mRNA）则存在于树突中。本研究评估了树突特异性RNA转运以及mRNA分选进入细胞体和胞体-树突区室在培养的发育中的海马神经元中首次出现的时间。采用³H-尿苷脉冲追踪范式来评估新合成的RNA从细胞核中的合成位点转运到发育中的神经突中的情况。通过原位杂交在不同发育阶段评估编码肌动蛋白、微管蛋白、GAP-43和MAP2的mRNA以及多聚腺苷酸RNA和rRNA的细胞内分布。新合成的RNA在发育早期就转运到发育中的轴突和树突中，但随着神经元成熟，仅转运到树突中。在成熟神经元中局限于细胞体的微管蛋白、GAP-43和肌动蛋白mRNA在所有发育阶段都仅在神经元细胞体中被发现。存在于成熟神经元树突中的MAP2 mRNA在培养2或3天的神经元中水平非常低，在树突中无法检测到。MAP2 mRNA的总体水平随时间增加，到培养5 - 7天时，在一些树突中可检测到MAP2 mRNA。多聚腺苷酸RNA和rRNA在包括轴突在内的发育中的神经突中可检测到。随着神经元成熟，树突中的多聚腺苷酸和rRNA水平增加，而轴突的标记减少。到培养10天时，轴突中多聚腺苷酸和rRNA的标记几乎消失。培养5至7天期间树突中多聚腺苷酸、rRNA和MAP2 mRNA水平的增加大致与其他树突特征的出现以及树突生长的开始相对应。
