A Chlamydomonas outer arm dynein mutant missing the alpha heavy chain

Area of Science:

• Cell Biology
• Biochemistry
• Genetics

Background:

• Chlamydomonas flagella are crucial for motility.
• Outer dynein arms are essential components of flagellar structure and function.
• The specific role of the alpha heavy chain in outer dynein arm assembly and function was not fully understood.

Purpose of the Study:

• To investigate the role of the alpha heavy chain in the assembly and function of the Chlamydomonas outer dynein arm.
• To characterize a novel mutant lacking the alpha heavy chain.

Main Methods:

• Isolation and characterization of a Chlamydomonas flagellar mutant (oda-11).
• Restriction fragment length polymorphism analysis to determine genetic linkage.
• Electron microscopy to examine flagellar axoneme structure.
• Measurement of flagellar beat frequency and swimming speed.

Main Results:

• The oda-11 mutant was identified as lacking the alpha heavy chain of the outer dynein arm but retaining beta and gamma heavy chains.
• Genetic analysis confirmed the mutation is linked to the alpha heavy chain gene.
• Electron microscopy revealed the absence of the outermost appendage in the oda-11 axoneme.
• The oda-11 mutant exhibited intermediate flagellar beat frequency (approx. 50 Hz) and swimming speed (119 µm/s) compared to wild-type and a mutant lacking the entire outer dynein arm.

Conclusions:

• The outer dynein arm of Chlamydomonas can be assembled even in the absence of the alpha heavy chain.
• The alpha heavy chain is likely located in the outermost appendage of the outer dynein arm.
• The outer dynein arm retains partial motility function when the alpha heavy chain is missing.