Key result
The dicky ticker mutation in Xenopus tropicalis, caused by a missense mutation in the muscle-specific chaperone unc45b, results in disrupted skeletal muscle myofibrillogenesis, paralysis, lack of heartbeat, and delayed Z-disc formation.
The study demonstrates that the myosin-specific chaperone unc45b is essential for vertebrate sarcomerogenesis and Z-body maturation.
unc45b is essential for vertebrate sarcomerogenesis; extends Xenopus models for myopathy research but leaves clinical translation open.
BACKGROUND: The protein components of mature skeletal muscle have largely been characterized, but the mechanics and sequence of their assembly during normal development remain an active field of study. Chaperone proteins specific to sarcomeric myosins have been shown to be necessary in zebrafish and invertebrates for proper muscle assembly and function. RESULTS: The Xenopus tropicalis mutation dicky ticker results in disrupted skeletal muscle myofibrillogenesis, paralysis, and lack of heartbeat, and maps to a missense mutation in the muscle-specific chaperone unc45b. Unc45b is known to be required for folding the head domains of myosin heavy chains, and mutant embryos fail to incorporate muscle myosin into sarcomeres. Mutants also show delayed polymerization of alpha-actinin-rich Z-bodies into the Z-disks that flank the myosin-containing A-band. CONCLUSIONS: The dicky ticker phenotype confirms that a requirement for myosin-specific chaperones is conserved in tetrapod sarcomerogenesis, and also suggests a novel role for myosin chaperone function in Z-body maturation.
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Geach et al. (2010) studied dicky ticker mutation (unc45b mutation). unc45b mutation (dicky ticker) and morpholino knockdown vs. Wild type embryos was evaluated on Myofibrillogenesis, paralysis, and heartbeat. The dicky ticker mutation in Xenopus tropicalis, caused by a missense mutation in the muscle-specific chaperone unc45b, results in disrupted skeletal muscle myofibrillogenesis, paralysis, lack of heartbeat, and delayed Z-disc formation.
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