Nikolic M, Dudek H, Kwon Y T, Ramos Y F, Tsai L H
Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Genes Dev. 1996 Apr 1;10(7):816-25. doi: 10.1101/gad.10.7.816.
Cyclin-dependent kinase 5(cdk5) is highly homologous to other members of the cdk family that are known to function in proliferating cells. Despite the structural similarity, cdk5-associated histone H1 kinase activity is only detectable in postmitotic neurons of the central nervous system (CNS). p35 is a neuronal-specific cdk5 regulator that activates cdk5 kinase activity upon association. The cdk5/p35 kinase activity increases during the progression of CNS neurogenesis, suggesting a function of cdk5 in neuronal differentiation. Here we show that both cdk5 and p35 proteins are present in the growth cones of developing neurons. The staining pattern of cdk5 in the growth cones is similar to that of actin filaments but not microtubules. To address the functional significance of the cdk5/p35 kinase in neurogenesis, we ectopically expressed wild-type or mutant kinases in cortical cultures. Expression of dominant-negative mutants of cdk5 (cdk5N144 and cdk5T33) inhibited neurite outgrowth, which was rescued by coexpression of the wild-type proteins. A similar extent of neurite outgrowth inhibition was obtained by transfection of an antisense p35 construct, which in turn was only rescued by p35 but not cdk5 coexpression. In contrast, longer neurites were elaborated in neurons that coexpressed exogenous cdk5 and p35. These observations suggest that the cdk5/p35 kinase plays a critical role in neurite outgrowth during neuronal differentiation.
细胞周期蛋白依赖性激酶5（cdk5）与细胞周期蛋白依赖性激酶（cdk）家族的其他成员高度同源，这些成员已知在增殖细胞中发挥作用。尽管结构相似，但cdk5相关的组蛋白H1激酶活性仅在中枢神经系统（CNS）的有丝分裂后神经元中可检测到。p35是一种神经元特异性的cdk5调节剂，与cdk5结合后可激活其激酶活性。在中枢神经系统神经发生过程中，cdk5/p35激酶活性增加，提示cdk5在神经元分化中发挥作用。在这里，我们显示cdk5和p35蛋白均存在于发育中神经元的生长锥中。cdk5在生长锥中的染色模式与肌动蛋白丝相似，但与微管不同。为了探讨cdk5/p35激酶在神经发生中的功能意义，我们在皮质培养物中异位表达野生型或突变型激酶。cdk5显性负性突变体（cdk5N144和cdk5T33）的表达抑制了神经突的生长，野生型蛋白的共表达可挽救这种抑制。转染反义p35构建体可获得类似程度的神经突生长抑制，而这种抑制反过来仅可通过p35共表达而不是cdk5共表达来挽救。相反，共表达外源性cdk5和p35的神经元中形成了更长的神经突。这些观察结果表明，cdk5/p35激酶在神经元分化过程中的神经突生长中起关键作用。
