Paralysis and delayed Z-disc formation in the Xenopus tropicalis unc45b mutant dicky ticker.
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.
Geach
Timothy J
TJ
Division of Developmental Biology, MRC-National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK.
Zimmerman
Lyle B
LB
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D005804:Genes, Lethal; D018832:Molecular Chaperones / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D024510:Muscle Development; D020125:Mutation, Missense; D009210:Myofibrils / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D012518:Sarcomeres / Q000378:metabolism; D016415:Sequence Alignment; D014981:Xenopus / Q000196:embryology* / Q000378:metabolism; D015027:Zebrafish
D018832:Molecular Chaperones; D009218:Myosins