Dok-7 promotes slow muscle integrity as well as neuromuscular junction formation in a zebrafish model of congenital myasthenic syndromes.
The small signalling adaptor protein Dok-7 has recently been reported as an essential protein of the neuromuscular junction (NMJ). Mutations resulting in partial loss of Dok-7 activity cause a distinct limb-girdle subtype of the inherited NMJ disorder congenital myasthenic syndromes (CMSs), whereas complete loss of Dok-7 results in a lethal phenotype in both mice and humans. Here we describe the zebrafish orthologue of Dok-7 and study its in vivo function. Dok-7 deficiency leads to motility defects in zebrafish embryos and larvae. The relative importance of Dok-7 at different stages of NMJ development varies; it is crucial for the earliest step, the formation of acetylcholine receptor (AChR) clusters in the middle of the muscle fibre prior to motor neuron contact. At later stages, presence of Dok-7 is not absolutely essential, as focal and non-focal synapses do form when Dok-7 expression is downregulated. These contacts however are smaller than in the wild-type zebrafish, reminiscent of the neuromuscular endplate pathology seen in patients with DOK7 mutations. Intriguingly, we also observed changes in slow muscle fibre arrangement; previously, Dok-7 has not been linked to functions other than postsynaptic AChR clustering. Our results suggest an additional role of Dok-7 in muscle. This role seems to be independent of the muscle-specific tyrosine kinase MuSK, the known binding partner of Dok-7 at the NMJ. Our findings in the zebrafish model contribute to a better understanding of the signalling pathways at the NMJ and the pathomechanisms of DOK7 CMSs.
Müller
Juliane S
JS
Institute of Human Genetics, International Centre for Life, Newcastle University, Central Parkway, Newcastle Upon Tyne NE1 3BZ, UK. juliane.mueller@ncl.ac.uk
Jepson
Catherine D
CD
Laval
Steven H
SH
Bushby
Kate
K
Straub
Volker
V
Lochmüller
Hanns
H
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D005455:Fluorescent Antibody Technique; D040461:Gene Components; D005786:Gene Expression Regulation / Q000502:physiology*; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000294:innervation / Q000378:metabolism*; D020294:Myasthenic Syndromes, Congenital / Q000503:physiopathology*; D009469:Neuromuscular Junction / Q000378:metabolism* / Q000503:physiopathology; D011950:Receptors, Cholinergic / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D017931:DNA Primers; D009124:Muscle Proteins; D011950:Receptors, Cholinergic; D029961:Zebrafish Proteins; C551629:dok7 protein, zebrafish