Probable muscle-intrinsic activator of MUSK that plays an essential role in neuromuscular synaptogenesis. Acts in aneural activation of MUSK and subsequent acetylcholine receptor (AchR) clustering in myotubes. Induces autophosphorylation of MUSK. Homodimer. Forms a heterotetramer composed of 2 DOK7 and 2 MUSK molecules which facilitates MUSK trans-autophosphorylation on tyrosine residue and activation. Interacts (via IRS-type PTB domain) with MUSK (via cytoplasmic part); requires MUSK phosphorylation. Accumulates at neuromuscular junctions. Expressed in the central region encompassing the endplate area of the diaphragm muscles at day 14.5 of embryonic development (14.5 dpc), when AChRs cluster in a nerve- and agrin-independent manner. The PH domain mediated binding to phospholipids with phosphoinositol headgroups. Affinity is highest for phosphatidyl 3,4,5-trisphosphate, followed by phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 4,5-bisphosphate. Mice are immobile at birth and die shortly thereafter. They do not form neither acetylcholine receptor clusters nor neuromuscular synapses.