Calaxin is a key factor for calcium-dependent waveform control in zebrafish sperm

Area of Science:

• Cell Biology
• Biochemistry
• Developmental Biology

Background:

• Calcium ions are crucial for regulating the waveform of motile cilia and flagella.
• Calaxin is the sole known molecule mediating calcium-dependent regulation in ascidians.
• Previous studies indicated Calaxin stabilizes outer arm dynein (OAD) and its absence causes primary ciliary dyskinesia.

Purpose of the Study:

• To elucidate the calcium-dependent and independent functions of Calaxin in ciliary and flagellar motility.
• To differentiate the roles of Calaxin in OAD stabilization versus waveform regulation.

Main Methods:

• Generated transgenic zebrafish expressing a calcium-binding deficient mutant (E130A-Calaxin).
• Assessed OAD levels and ciliary/flagellar movement in mutant zebrafish.
• Performed quantitative analysis of flagellar beating patterns.

Main Results:

• E130A-Calaxin expression rescued OAD reduction and abnormal ciliary movement in calaxin-deficient sperm and left-right organizer cilia.
• These rescue effects demonstrate that Calaxin's OAD stabilization function is calcium-independent.
• Calcium-induced asymmetric beating was not restored in E130A-Calaxin expressing sperm, indicating calcium-dependence for this function.

Conclusions:

• Calaxin acts as a calcium-independent stabilizer of outer arm dynein.
• Calaxin's calcium-binding ability is essential for regulating asymmetric flagellar beating.
• This study delineates the distinct calcium-dependent and independent roles of Calaxin in ciliary function.