Identification of the interactome of muscular LAP proteins, Erbin, Lano, and Scribble, their involvement in the endocytic recycling at the neuromuscular synapse, and their role in myogenesis

LAP(富含亮氨酸重复序列和PDZ结构域)蛋白Erbin、Lano和Scribble在骨骼肌细胞谱系中的作用，特别是在神经肌肉连接(NMJ)中的作用，目前大多尚不清楚。我们的初步数据表明，LAP蛋白在NMJ、肌肉细胞、神经末梢和终末雪旺细胞三个细胞实体中表达不同。首先，这三种LAP蛋白都在肌纤维中表达，并聚集在突触后装置下，Erbin和Scribble与NMJ的烟碱型乙酰胆碱受体(AChR)聚集体完美匹配。第二，在体内消融Erbin与NMJ的AChR聚集体显著减少以及LANO和Scribble的上调有关。第三，已报道的Erbin PDZ结构域与ErbB受体的相互作用对Erbin与NMJ的定位并不重要。第四，最近有报道称Scribble和Erbin分别参与了小鼠中枢神经系统或秀丽线虫上皮细胞的内吞运输。第五，Scribble作为一种支架和细胞极性蛋白参与了肌肉卫星细胞命运的决定。Erbin和Lano也被称为支架蛋白，但它们是否在细胞极性中发挥作用尚不清楚。但在肌细胞分化过程中，Erbin和LANO转录量增加。基于这些观察，我们旨在提出以下问题以更好地理解Erbin、Lano和Scribble在肌肉细胞生物学中的作用：1.Erbin、Lano和Scribble如何参与肌肉细胞生物学、突触后装置的形成或维持以及它们的相互作用体成员是什么？2.LAP蛋白是否也像AChRs一样参与NMJ突触后装置蛋白的内吞运输？3.Erbin或Lano是否像Scribble那样影响肌肉干细胞的增殖？

The role of LAP (leucine rich repeat and PDZ domain containing) proteins, Erbin, Lano, and Scribble, in the skeletal muscle cell lineage, especially with emphasis on the neuromuscular junction (NMJ), is mostly unknown. Our preliminary data demonstrate that LAP proteins are expressed differently in the three cell entities of the NMJ, muscle cell, nerve ending, terminal Schwann cell. First, all three LAP proteins are expressed in the myofibers and accumulated underneath the postsynaptic apparatus, with Erbin and Scribble matching perfectly with the aggregates of the nicotinic acetylcholine receptors (AChR) at the NMJ. Second, in vivo ablation of Erbin is associated with significantly smaller aggregates of AChRs at NMJs and up-regulation of Lano and Scribble. Third, the reported interaction of the Erbin PDZ domain with ErbB receptors is not important for positioning of Erbin with NMJs. Fourth, recently Scribble and Erbin were reported being involved in endocytic trafficking in the central nervous system of mice, or epithelial cells in Caenorhabditis elegans, respectively. Fifth, Scribble as a scaffold and cell-polarity protein is involved in muscle satellite cell fate decision. Erbin and Lano are also known as scaffold proteins, but whether they play a role in cell-polarity is unknown. However, Erbin and Lano transcript amount increases during muscle cell differentiation. Based on these observations, we aim to ask the following questions to better understand the role of Erbin, Lano, and Scribble in muscle cell biology: 1. How are Erbin, Lano, and Scribble involved in muscle cell biology, and formation or maintenance of the postsynaptic apparatus and what are the members of their interactome? 2. Are LAP proteins also involved in endocytic trafficking of postsynaptic apparatus proteins at the NMJ, like the AChRs? 3. Do Erbin or Lano influence muscle stem cell proliferation, like it was reported for Scribble?