Gilchrist Susan, Gilbert Nick, Perry Paul, Ostlund Cecilia, Worman Howard J, Bickmore Wendy A
MRC Human Genetics Unit, Crewe Road, Edinburgh EH4 2XU, UK.
BMC Cell Biol. 2004 Dec 13;5(1):46. doi: 10.1186/1471-2121-5-46.
Recent interest in the function of the nuclear lamina has been provoked by the discovery of lamin A/C mutations in the laminopathy diseases. However, it is not understood why mutations in lamin A give such a range of tissue-specific phenotypes. Part of the problem in rationalising genotype-phenotype correlations in the laminopathies is our lack of understanding of the function of normal and mutant lamin A. To investigate this we have used photobleaching in human cells to analyse the dynamics of wild-type and mutant lamin A protein at the nuclear periphery.
We have found that a large proportion of wild-type lamin A at the nuclear periphery is immobile, but that there is some slow movement of lamin A within the nuclear lamina. The mobility of an R482W mutant lamin A was indistinguishable from wild-type, but increased mobility of L85R and L530P mutant proteins within the nuclear lamina was found. However, the N195K mutant shows the most enhanced protein mobility, both within the nucleoplasm and within the lamina.
The slow kinetics of lamin A movement is compatible with its incorporation into a stable polymer that only exchanges subunits very slowly. All of the myopathy-associated lamin A mutants that we have studied show increased protein movement compared with wild-type. In contrast, the dynamic behaviour of the lipodystrophy-associated lamin A mutant was indistinguishable from wild-type. This supports the hypothesis that the underlying defect in lamin A function is quite distinct in the laminopathies that affect striated muscle, compared to the diseases that affect adipose tissue. Our data are consistent with an alteration in the stability of the lamin A molecules within the higher-order polymer at the nuclear lamina in myopathies.
核纤层蛋白病中lamin A/C突变的发现引发了近期对核纤层功能的关注。然而，尚不清楚lamin A突变为何会导致一系列组织特异性表型。在解释核纤层蛋白病中基因型与表型的相关性时，部分问题在于我们对正常和突变型lamin A功能的理解不足。为了研究这一问题，我们利用人细胞中的光漂白技术分析野生型和突变型lamin A蛋白在核周边的动态变化。
我们发现，核周边的大部分野生型lamin A是固定不动的，但lamin A在核纤层内存在一些缓慢移动。R482W突变型lamin A的移动性与野生型无差异，但发现L85R和L530P突变蛋白在核纤层内的移动性增加。然而，N195K突变体在核质和核纤层内均表现出最强的蛋白移动性。
lamin A移动的缓慢动力学与它掺入仅非常缓慢交换亚基的稳定聚合物相一致。我们研究的所有与肌病相关的lamin A突变体与野生型相比，蛋白移动性均增加。相比之下，与脂肪营养不良相关的lamin A突变体的动态行为与野生型无差异。这支持了这样一种假说，即与影响脂肪组织的疾病相比，影响横纹肌的核纤层蛋白病中lamin A功能的潜在缺陷截然不同。我们的数据与肌病中核纤层高阶聚合物内lamin A分子稳定性的改变一致。
