Toutenhoofd Sonja L, Strehler Emanuel E
Program in Molecular Neuroscience, Mayo Graduate School and Department of Biochemistry and Molecular Biology, Mayo Clinic, 200 First Street S.W., Rochester, MN 55905, USA.
Biochim Biophys Acta. 2002 Nov 4;1600(1-2):95-104. doi: 10.1016/s1570-9639(02)00449-1.
Calmodulin (CaM), the principal mediator of the calcium signal, regulates numerous processes pertinent to neural function. Mammalian CaM is generated from three genes that give rise to five distinct transcripts. To determine the regulation of individual CaM transcripts in neurons, we assessed their abundance during differentiation of human IMR-32 neuroblastoma cells. Northern analysis revealed that the 4.1 kb CALM1 transcript was specifically upregulated about two-fold during differentiation, and that this increase correlated with neurite extension. By contrast, the CALM2 and CALM3 mRNAs as well as the 1.7 kb CALM1 transcript showed an initial increase but then returned to levels close to, or only slightly above, controls. The increase in the 4.1 kb transcript was largely due to its specific stabilization in differentiated cells. However, total cellular CaM levels did not change significantly throughout differentiation. To begin to address whether the 4.1 kb CALM1 transcript might play a unique role in providing local CaM pools, we determined its localization in differentiated IMR-32 cells using in situ hybridization. The 4.1 kb CALM1 transcript localized to the cell body, but was also present within extending neurites. This finding agrees with in vivo studies showing elevated levels of the 4.1 kb CALM1 transcript in adult rat central neurons and the presence of CALM1 transcripts in dendrites, and establishes a human in vitro model system to study individual CaM transcripts with respect to neuronal functions.
钙调蛋白（CaM）是钙信号的主要介导因子，调控着众多与神经功能相关的过程。哺乳动物的CaM由三个基因产生，这三个基因产生五种不同的转录本。为了确定神经元中单个CaM转录本的调控情况，我们评估了它们在人IMR-32神经母细胞瘤细胞分化过程中的丰度。Northern分析显示，4.1 kb的CALM1转录本在分化过程中特异性地上调了约两倍，并且这种增加与神经突延伸相关。相比之下，CALM2和CALM3 mRNA以及1.7 kb的CALM1转录本最初有所增加，但随后又回到接近或仅略高于对照的水平。4.1 kb转录本的增加主要是由于其在分化细胞中的特异性稳定。然而，在整个分化过程中，细胞内总的CaM水平没有显著变化。为了开始探讨4.1 kb的CALM1转录本是否可能在提供局部CaM库方面发挥独特作用，我们使用原位杂交确定了它在分化的IMR-32细胞中的定位。4.1 kb的CALM1转录本定位于细胞体，但也存在于延伸的神经突内。这一发现与体内研究结果一致，体内研究表明成年大鼠中枢神经元中4.1 kb的CALM1转录本水平升高，并且树突中存在CALM1转录本，从而建立了一个人类体外模型系统，用于研究单个CaM转录本与神经元功能相关的问题。
