Loss of Smyhc1 or Hsp90alpha1 function results in different effects on myofibril organization in skeletal muscles of zebrafish embryos.
BACKGROUND
Myofibrillogenesis requires the correct folding and assembly of sarcomeric proteins into highly organized sarcomeres. Heat shock protein 90alpha1 (Hsp90alpha1) has been implicated as a myosin chaperone that plays a key role in myofibrillogenesis. Knockdown or mutation of hsp90alpha1 resulted in complete disorganization of thick and thin filaments and M- and Z-line structures. It is not clear whether the disorganization of these sarcomeric structures is due to a direct effect from loss of Hsp90alpha1 function or indirectly through the disorganization of myosin thick filaments.


RESULTS
In this study, we carried out a loss-of-function analysis of myosin thick filaments via gene-specific knockdown or using a myosin ATPase inhibitor BTS (N-benzyl-p-toluene sulphonamide) in zebrafish embryos. We demonstrated that knockdown of myosin heavy chain 1 (myhc1) resulted in sarcomeric defects in the thick and thin filaments and defective alignment of Z-lines. Similarly, treating zebrafish embryos with BTS disrupted thick and thin filament organization, with little effect on the M- and Z-lines. In contrast, loss of Hsp90alpha1 function completely disrupted all sarcomeric structures including both thick and thin filaments as well as the M- and Z-lines.


CONCLUSIONS
Together, these studies indicate that the hsp90alpha1 mutant phenotype is not simply due to disruption of myosin folding and assembly, suggesting that Hsp90alpha1 may play a role in the assembly and organization of other sarcomeric structures.
Codina
Marta
M
Center of Marine Biotechnology, Biotechnology Institute, University of Maryland, Baltimore, Maryland, United States of America.
Li
Junling
J
Gutiérrez
Joaquim
J
Kao
Joseph P Y
JP
Du
Shao Jun
SJ
D000818:Animals; D055785:Gene Knockdown Techniques; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000502:physiology*; D018482:Muscle, Skeletal / Q000196:embryology* / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000235:genetics / Q000502:physiology*; D015027:Zebrafish / Q000196:embryology*
D018841:HSP90 Heat-Shock Proteins; D018995:Myosin Heavy Chains