Abstract 13828: Fhos Expression is Required for Striated Flight Muscle Formation and Viability in Flies
Recently we demonstrated that a peptide variant of FHOD3, an actin filament regulator, is associated with Hypertrophic Cardiomyopathy (HCM), and that the FHOD3 D. melanogaster homologue fhos is required for normal heart contractile function. Based upon the association of FHOD3 with HCM, we hypothesized that fhos is required for normal muscle development in flies. Using a Fhos-Gal4 driver line regulating GFP expression we demonstrated fhos gene expression in both flight and jump muscles. Using RNA interference we found fhos expression to be required in the mesoderm (HOW-Gal4 driver (p=2.81E-05)) and muscle (MEF2-Gal4 driver (p=0.000445)) for flies to develop past the eclosion stage. By comparison, fhos knockdown in motor neurons (D42- Gal4) and early mesoderm (Twist-Gal4) was not lethal. Histological analysis following fhos silencing demonstrated a striking disorganization of muscle fibers in the flight muscles by PTAH staining; jump muscles were unaffected. Anti-α-Actinin immunohistochemistry demonstrated a loss of muscle striations and disorder of Z-bands selectively in flight muscles following fhos muscle silencing. Western blot analysis confirmed α-Actinin expression after fhos knockdown and quantitative PCR analysis demonstrated no significant reduction in expression of tropomyosin, αMHC, and dystrophin in fhos silenced flies compared with controls, suggesting that the disorganized muscle contractile apparatus is likely a post transcriptional effect. Flight muscles can be compared to mammalian cardiac muscle due to their involuntary contractions, which may explain why the fiber disorganization phenotype was seen in this muscle type. We analyzed the role of fhos in flight muscle function using a mutant fly line bearing a P-element insertion into the fhos gene. The corresponding flies are viable after eclosion and show a significant decrease in fhos expression in homozygous flies (p=4.79E-06). Fhos P-element flies demonstrated a defect in flight as measured by a cylinder drop assay. These data demonstrate that fhos is required for the normal development of flight muscles and flight. These results in a fly model support an important role for fhos/FHOD3 in muscle development and support a role for FHOD3 in muscle diseases, including HCM.
- © 2013 by American Heart Association, Inc.