Zebrafish relatively relaxed mutants have a ryanodine receptor defect, show slow swimming and provide a model of multi-minicore disease.


Journal Article

Wild-type zebrafish embryos swim away in response to tactile stimulation. By contrast, relatively relaxed mutants swim slowly due to weak contractions of trunk muscles. Electrophysiological recordings from muscle showed that output from the CNS was normal in mutants, suggesting a defect in the muscle. Calcium imaging revealed that Ca(2+) transients were reduced in mutant fast muscle. Immunostaining demonstrated that ryanodine and dihydropyridine receptors, which are responsible for Ca(2+) release following membrane depolarization, were severely reduced at transverse-tubule/sarcoplasmic reticulum junctions in mutant fast muscle. Thus, slow swimming is caused by weak muscle contractions due to impaired excitation-contraction coupling. Indeed, most of the ryanodine receptor 1b (ryr1b) mRNA in mutants carried a nonsense mutation that was generated by aberrant splicing due to a DNA insertion in an intron of the ryr1b gene, leading to a hypomorphic condition in relatively relaxed mutants. RYR1 mutations in humans lead to a congenital myopathy, multi-minicore disease (MmD), which is defined by amorphous cores in muscle. Electron micrographs showed minicore structures in mutant fast muscles. Furthermore, following the introduction of antisense morpholino oligonucleotides that restored the normal splicing of ryr1b, swimming was recovered in mutants. These findings suggest that zebrafish relatively relaxed mutants may be useful for understanding the development and physiology of MmD.

Full Text

Cited Authors

  • Hirata, H; Watanabe, T; Hatakeyama, J; Sprague, SM; Saint-Amant, L; Nagashima, A; Cui, WW; Zhou, W; Kuwada, JY

Published Date

  • August 2007

Published In

Volume / Issue

  • 134 / 15

Start / End Page

  • 2771 - 2781

PubMed ID

  • 17596281

Pubmed Central ID

  • 17596281

Electronic International Standard Serial Number (EISSN)

  • 1477-9129

International Standard Serial Number (ISSN)

  • 0950-1991

Digital Object Identifier (DOI)

  • 10.1242/dev.004531


  • eng