Mutations causing DOK7 congenital myasthenia ablate functional motifs in Dok-7

Area of Science:

• Molecular Biology
• Neuroscience
• Genetics

Background:

• Dok-7 (Downstream of Kinase 7) activates MuSK (muscle-specific receptor-tyrosine kinase).
• Dok-7 and MuSK are vital for neuromuscular synaptogenesis.
• Mutations in DOK7 cause congenital myasthenic syndrome (CMS) with impaired neuromuscular junctions.

Purpose of the Study:

• To investigate novel functional elements in Dok-7 beyond its known NH2-terminal PH and PTB domains.
• To elucidate the role of Dok-7's subcellular localization in MuSK activation and neuromuscular junction formation.
• To understand the molecular basis of DOK7-CMS related to Dok-7's COOH-terminal region.

Main Methods:

• Identification of a nuclear export signal (NES) in Dok-7's COOH-terminal region.
• Demonstration of NES-mediated cytoplasmic localization's importance for Dok-7/MuSK interaction.
• Analysis of Dok-7's NH2-terminal PH domain's role in nuclear import.
• Investigation of Src homology 2 (SH2) target motifs in Dok-7's COOH-terminal moiety.
• Assessment of CMS-associated missense mutations in PH and PTB domains.

Main Results:

• A chromosome region maintenance 1-dependent NES was identified in the Dok-7 COOH-terminal moiety.
• NES-mediated cytoplasmic localization of Dok-7 is crucial for MuSK interaction in myotubes.
• The NH2-terminal PH domain mediates Dok-7 nuclear import.
• Dok-7's COOH-terminal SH2 target motifs are active and essential for MuSK activation.
• CMS-associated missense mutations in PH or PTB domains inactivate Dok-7.

Conclusions:

• Dok-7's COOH-terminal NES and SH2 target motifs are critical for Dok-7/MuSK signaling in neuromuscular synaptogenesis.
• Disruption of these functional elements in Dok-7 likely causes the neuromuscular junction defects in DOK7-CMS.
• Understanding these elements provides insights into congenital myasthenic syndromes and neuromuscular development.