LAP proteins are localized at the postsynaptic membrane of neuromuscular junctions and appear to modulate synaptic morphology and transmission

Authors
Kravic B, Huraskin D, Frick AD, Jung J, Redai V, Palmisano R, Marchetto S, Borg JP, Mei L, Hashemolhosseini S

Lab
Institut für Biochemie, Friedrich-Alexander Universität Erlangen, Nürnberg Fahrstraße 17, D-91054, Erlangen, Germany

Journal
J Neurochem.

Abstract
Erbin, Lano, Scribble, and Densin-180 belong to LAP [leucine-rich repeats (LRRs) and PDZ domain] adaptor proteins involved in cell signaling pathways. Previously, we identified Erbin, Lano and Scribble, but not Densin-180, in muscle cells, where they are involved in regulating the aggregation of nicotinic acetylcholine receptors (AChR) in vitro. Here, we analysed their cellular localization at the neuromuscular junction (NMJ) in skeletal muscles of mice. Erbin, Lano and Scribble were significantly accumulated at NMJs and localized in different synaptic cells. Moreover, we used mouse mutants to analyse the role of Erbin at the NMJ. We used two Erbin mutant mouse strains that either completely lack Erbin protein (Erbinnull/null ) or express a truncated Erbin mutant where the carboxy-terminal PDZ domain is replaced by β-galactosidase (ErbinΔC/ΔC ) thereby abolishing its interaction with ErbB receptor tyrosine kinases. Neither the lack of the PDZ domain of Erbin, nor its complete absence interfered with the general localization of LAP proteins at NMJs, but Lano and Scribble transcript levels were upregulated in homozygous Erbin-null muscles. Further, grip strength was reduced and neural transmission impaired in homozygous aged Erbin-null but not Erbin-ΔC mice. Erbin-null skeletal muscles did not reveal any conspicuous impairment of the muscle fiber. Localization of other NMJ marker proteins was not affected either. Quantitative 3D morphometry showed that NMJs of Erbin-null muscles were significantly smaller and fragmented in the soleus. We speculate that Erbin, Lano and Scribble act at the postsynaptic membrane of NMJs in a concerted fashion to regulate AChR cluster morphology and neural transmission.

BIOSEB Instruments Used:
Grip strength test (BIO-GS3)