Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA, USA.
Cellular and Molecular Synaptic Function Unit, Okinawa Institute of Science and Technology - Graduate University, Kunigami, Okinawa, Japan.
PeerJ. 2013 Feb 12;1:e7. doi: 10.7717/peerj.7. Print 2013.
Assembly of the actin cytoskeleton is an important part of formation of neurites in developing neurons. Tropomodulin, a tropomyosin-dependent capping protein for the pointed end of the actin filament, is one of the key players in this process. Tropomodulin binds tropomyosin in two binding sites. Tmod1 and Tmod2, tropomodulin isoforms found in neurons, were overexpressed in PC12 cells, a model system for neuronal differentiation. Tmod1 did not affect neuronal differentiation; while cells expressing Tmod2 showed a significant reduction in the number and the length of neurites. Both tropomodulins bind short α-, γ- and δ-tropomyosin isoforms. Mutations in one of the tropomyosin-binding sites of Tmod1, which increased its affinity to short γ- and δ-tropomyosin isoforms, caused a decrease in binding short α-tropomyosin isoforms along with a 2-fold decrease in the length of neurites. Our data demonstrate that Tmod1 is involved in neuronal differentiation for proper neurite formation and outgrowth, and that Tmod2 inhibits these processes. The mutations in the tropomyosin-binding site of Tmod1 impair neurite outgrowth, suggesting that the integrity of this binding site is critical for the proper function of Tmod1 during neuronal differentiation.
肌动蛋白细胞骨架的组装是发育神经元中神经突形成的重要组成部分。原肌球蛋白依赖性肌动蛋白纤维尖端封盖蛋白 Tropomodulin 是该过程中的关键参与者之一。Tropomodulin 在两个结合位点结合肌球蛋白。在神经元中发现的 Tropomodulin 同种型 Tmod1 和 Tmod2 在 PC12 细胞中过表达，PC12 细胞是神经元分化的模型系统。Tmod1 不影响神经元分化；而表达 Tmod2 的细胞的神经突数量和长度显著减少。两种 Tropomodulins 都结合短的 α-、γ-和 δ-肌球蛋白同种型。Tmod1 的一个肌球蛋白结合位点的突变增加了其与短的 γ-和 δ-肌球蛋白同种型的亲和力，导致与短的 α-肌球蛋白同种型的结合减少，同时神经突的长度减少了 2 倍。我们的数据表明，Tmod1 参与神经元分化以形成和延伸适当的神经突，而 Tmod2 抑制这些过程。Tmod1 肌球蛋白结合位点的突变会损害神经突的生长，这表明该结合位点的完整性对于神经元分化过程中 Tmod1 的正常功能至关重要。
