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

在骨骼肌细胞谱系中，尤其是在神经肌肉接头（NMJ）中，富含亮氨酸重复序列和PDZ结构域的蛋白Erbin、Lano和Scribble的作用大多是未知的。我们的初步数据表明，在NMJ的三个细胞实体，肌肉细胞，神经末梢，终末雪旺细胞中，EMP3蛋白的表达不同。首先，所有三种蛋白质都在肌纤维中表达，并在突触后器下方积累，Erbin和Scribble与NMJ处的烟碱乙酰胆碱受体（AChR）的聚集体完美匹配。其次，Erbin的体内消融与NMJ处AChR的显著较小聚集体以及Lano和Scribble的上调相关。第三，所报道的Erbin PDZ结构域与ErbB受体的相互作用对于Erbin与NMJ的定位并不重要。第四，最近报道了Scribble和Erbin分别参与小鼠中枢神经系统或秀丽隐杆线虫上皮细胞的内吞运输。第五，Scribble作为支架和细胞极性蛋白参与肌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。然而，Erbin和Lano转录物的量在肌细胞分化过程中增加。基于这些观察，我们的目标是提出以下问题，以更好地了解Erbin，Lano和Scribble在肌肉细胞生物学中的作用：1。Erbin、Lano和Scribble如何参与肌细胞生物学，以及突触后装置的形成或维持，它们的相互作用体成员是什么？2. NMJ的突触后器蛋白（如AChRs）的内吞运输是否也与NMJ的突触后器蛋白有关？3. Erbin或Lano是否会影响肌肉干细胞增殖，就像Scribble报道的那样？

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?