Lack of the myotendinous junction marker col22a1 results in posture and locomotion disabilities in zebrafish.

The myotendinous junction (MTJ) is essential for the integrity of the musculoskeletal unit. Here, we show that gene ablation of the MTJ marker col22a1 in zebrafish results in MTJ dysfunction but with variable degrees of expression and distinct phenotypic classes. While most individuals reach adulthood with no overt muscle phenotype (class 1), a subset of the progeny displays severe movement impairment and die before metamorphosis (class 2). Yet all mutants display muscle weakness due to ineffective muscle force transmission that is ultimately detrimental for class-specific locomotion-related functions. Movement impairment at the critical stage of swimming postural learning causes class 2 larval death by compromising food intake. In class 1 adults, intensive exercise is required to uncover a decline in muscle performance, accompanied by higher energy demand and mitochondrial adaptation. This study underscores COL22A1 as a candidate gene for myopathies associated with dysfunctional force transmission and anticipates a phenotypically heterogeneous disease.