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Updated: Aug 14, 2026
Analysis of Embryonic and Larval Zebrafish Skeletal Myofibers from Dissociated Preparations
Published on: November 13, 2013
Non-sense mutations in the dihydropyridine receptor beta1 gene, CACNB1, paralyze zebrafish relaxed mutants
Weibin Zhou1, Louis Saint-Amant, Hiromi Hirata
1Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, 48109-1048, USA.
Abstract:
Contractions by skeletal muscle require proper excitation-contraction (EC) coupling, whereby depolarization of the muscle membrane leads to an increase in cytosolic Ca(2+) and contraction. Changes in membrane voltage are detected by dihydropyridine receptors (DHPR) that directly interact with and activate ryanodine receptors to release Ca(2+) from the sarcoplasmic reticulum into the cytosol. A genetic screen for motility mutations isolated a new allele of the immotile zebrafish mutant relaxed. Muscles in relaxed embryos do not contract in response to potassium chloride (KCl) thus appear unresponsive to membrane depolarization, but do contract when stimulated by caffeine, an agonist of ryanodine receptors. This suggests that relaxed mutant muscles are defective in EC coupling. Indeed, immunohistochemical analysis demonstrated that mutants lack DHPRs in skeletal muscles. The mutant phenotype results from non-sense mutations in the zebrafish CACNB1 gene that encodes the DHPR beta1 subunit. The zebrafish CACNB1 gene is expressed in skeletal muscles, PNS and CNS. Electrophysiological recordings showed no obvious abnormalities in the motor output of relaxed mutants, presumably due to redundancy provided by other beta subunits. The structural and functional homology of CACNB1 in zebrafish and mammals, suggests that zebrafish can be useful for studying EC coupling and potential neuronal function of CACNB1.
Insights
Mutant zebrafish lacking dihydropyridine receptors (DHPRs) in skeletal muscles exhibit defective excitation-contraction coupling. This study identifies a CACNB1 gene mutation causing this defect, highlighting zebrafish as a model for muscle function research.
Area of Science:
- Muscle physiology
- Molecular biology
- Genetics
Background:
- Excitation-contraction (EC) coupling is crucial for skeletal muscle contraction, involving membrane depolarization detected by dihydropyridine receptors (DHPRs).
- DHPRs directly activate ryanodine receptors, initiating calcium release from the sarcoplasmic reticulum, leading to muscle contraction.
Purpose of the Study:
- To investigate the genetic basis of defective EC coupling in the zebrafish mutant 'relaxed'.
- To characterize the role of the CACNB1 gene and its encoded DHPR beta1 subunit in skeletal muscle function.
Main Methods:
- Genetic screening for motility mutations in zebrafish.
- Electrophysiological recordings to assess muscle response to depolarization (KCl) and ryanodine receptor activation (caffeine).
- Immunohistochemical analysis to detect DHPR expression in skeletal muscles.
Main Results:
- The 'relaxed' zebrafish mutant exhibits immotility and unresponsive skeletal muscles to depolarization but responds to caffeine.
- Immunohistochemistry revealed a complete absence of DHPRs in the skeletal muscles of 'relaxed' mutants.
- Mutations in the CACNB1 gene, encoding the DHPR beta1 subunit, were identified as the cause of the observed phenotype.
Conclusions:
- The CACNB1 gene is essential for DHPR assembly and function in zebrafish skeletal muscle EC coupling.
- Zebrafish CACNB1 exhibits functional homology with mammalian counterparts, establishing zebrafish as a valuable model for studying EC coupling.
- Redundancy among DHPR beta subunits may explain the lack of motor output abnormalities in mutants, suggesting potential roles for CACNB1 in neuronal functions.
