Chiu S Y, Scherer S S, Blonski M, Kang S S, Messing A
Department of Neurophysiology, School of Medicine, University of Wisconsin, Madison 53706.
Glia. 1994 Sep;12(1):1-11. doi: 10.1002/glia.440120102.
We examined potassium channel gene expression of two members of the Shaker subfamily, MK1 and MK2, in sciatic nerves from rats and mice. In Northern blot analysis, MK1 and MK2 probes detected single transcripts of approximately 8 kb and approximately 9.5 kb, respectively, in sciatic nerve and brain from both species. Polymerase chain reaction amplification of a cDNA library of cultured rat Schwann cells using MK1- and MK2- specific primers produced DNA fragments that were highly homologous to MK1 and MK2. To determine whether these channel genes were axonally regulated, we performed Northern blot analysis of developing, permanently transected, and crushed rat sciatic nerves. The mRNA levels for both MK1 and MK2 increased from P1 to P15 and then declined modestly. Permanent nerve transection in adult animals resulted in a dramatic and permanent reduction in the mRNA levels for both MK1 and MK2, whereas normal levels of MK1 and MK2 were restored when regeneration was allowed to occur following crush injury. In all cases, MK1 and MK2 mRNA levels paralleled that of the myelin gene P0. Elevating the cAMP in cultured Schwann cells by forskolin, which mimics axonal contact but not myelination, did not induce detectable levels of MK1 and MK2 mRNA by Northern blot analysis. Further, the level of MK1 mRNA in the vagus nerve, which contains relatively fewer myelinating Schwann cells and relatively more non-myelinating Schwann cells than the sciatic nerve, is reduced relative to the sciatic nerve. In conclusion, we have identified two Shaker-like potassium channel genes in sciatic nerves whose expressions are regulated by axons. We suggest that MK1 and MK2 mRNA are expressed in high levels only in myelinating Schwann cells and that these Shaker-like potassium channel genes have specialized roles in these cells.
我们检测了大鼠和小鼠坐骨神经中Shaker亚家族的两个成员MK1和MK2的钾通道基因表达。在Northern印迹分析中，MK1和MK2探针分别在两种动物的坐骨神经和脑中检测到了大小约为8 kb和9.5 kb的单一转录本。使用MK1和MK2特异性引物对培养的大鼠雪旺细胞cDNA文库进行聚合酶链反应扩增，产生了与MK1和MK2高度同源的DNA片段。为了确定这些通道基因是否受轴突调节，我们对发育中的、永久性横断的和挤压伤的大鼠坐骨神经进行了Northern印迹分析。MK1和MK2的mRNA水平从出生后第1天（P1）到第15天升高，然后略有下降。成年动物永久性神经横断导致MK1和MK2的mRNA水平急剧且永久性降低，而挤压伤后允许再生时，MK1和MK2恢复到正常水平。在所有情况下，MK1和MK2的mRNA水平与髓鞘基因P0的水平平行。通过福司可林提高培养的雪旺细胞中的cAMP水平，福司可林模拟轴突接触但不模拟髓鞘形成，Northern印迹分析未检测到可检测水平的MK1和MK2 mRNA。此外，与坐骨神经相比，迷走神经中MK1 mRNA的水平降低，迷走神经中髓鞘形成雪旺细胞相对较少，非髓鞘形成雪旺细胞相对较多。总之，我们在坐骨神经中鉴定出两个类Shaker钾通道基因，其表达受轴突调节。我们认为MK1和MK2 mRNA仅在髓鞘形成雪旺细胞中高水平表达，并且这些类Shaker钾通道基因在这些细胞中具有特殊作用。
