MRC Centre for Developmental Neurobiology, King's College London, Guy's Campus, London, UK.
J Anat. 2010 Jun;216(6):692-704. doi: 10.1111/j.1469-7580.2010.01228.x. Epub 2010 Apr 9.
The microtubule-associated protein MAP1B has important roles in neural development, particularly in migrating and differentiating neurons. MAP1B is phosphorylated by glycogen synthase kinase 3beta (GSK-3beta) at a site that requires prior phosphorylation by another kinase four amino acid residues downstream of the GSK-3beta site, a so-called primed site, and at non-primed sites that have no such requirement. In developing mammalian neurons, MAP1B phosphorylated by GSK-3beta at primed and non-primed sites is distributed in spatially distinct patterns. Non-primed GSK-3beta-phosphorylated MAP1B sites are only expressed in axons and are present in the form of a gradient that is highest distally, towards the growth cone. In contrast, primed GSK-3beta-phosphorylated MAP1B sites are present throughout the neuron including the somato-dendritic compartment and uniformly throughout the axon. To examine the function of these two sites, we explored the evolutionary conservation of the spatial distribution of GSK-3beta primed and non-primed sites on MAP1B in vertebrate neurons. We immunostained spinal cord sections from embryonic or newly hatched representatives of all of the main vertebrate groups using phospho-specific antibodies to GSK-3beta primed and non-primed sites on MAP1B. This revealed a remarkable evolutionary conservation of the distribution of primed and non-primed GSK-3beta-phosphorylated MAP1B sites in developing vertebrate neurons. By analysing amino acid sequences of MAP1B we found that non-primed GSK-3beta sites are more highly conserved than primed sites throughout the vertebrates, suggesting that the latter evolved later. Finally, distinct distribution patterns of GSK-3beta primed and non-primed sites on MAP1B were preserved in cultured rat embryonic cortical neurons, opening up the possibility of studying the two sites in vitro.
微管相关蛋白 MAP1B 在神经发育中具有重要作用，特别是在迁移和分化的神经元中。MAP1B 可被糖原合酶激酶 3β（GSK-3β）在一个位点磷酸化，该位点需要在 GSK-3β 位点下游四个氨基酸残基处的另一个激酶预先磷酸化，即所谓的引发位点，以及在没有这种要求的非引发位点。在发育中的哺乳动物神经元中，MAP1B 被 GSK-3β 在引发和非引发位点磷酸化，其分布呈空间上不同的模式。非引发 GSK-3β 磷酸化的 MAP1B 位点仅在轴突中表达，并以一种梯度的形式存在，该梯度在向生长锥的远端最高。相比之下，引发 GSK-3β 磷酸化的 MAP1B 位点存在于整个神经元中，包括体树突区，并且在整个轴突中均匀分布。为了研究这两个位点的功能，我们研究了脊椎动物神经元中 MAP1B 上 GSK-3β 引发和非引发位点的空间分布在进化上的保守性。我们使用针对 MAP1B 上 GSK-3β 引发和非引发位点的磷酸化特异性抗体，对来自所有主要脊椎动物类群的胚胎或刚孵化的代表的脊髓切片进行免疫染色。这揭示了发育中的脊椎动物神经元中引发和非引发 GSK-3β 磷酸化 MAP1B 位点分布的惊人进化保守性。通过分析 MAP1B 的氨基酸序列，我们发现非引发 GSK-3β 位点在整个脊椎动物中比引发位点更保守，这表明后者是后来进化而来的。最后，在培养的大鼠胚胎皮质神经元中，MAP1B 上的 GSK-3β 引发和非引发位点的不同分布模式得以保留，这为在体外研究这两个位点提供了可能性。
