Aquaporin-3a Dysfunction Impairs Osmoadaptation in Post-Activated Marine Fish Spermatozoa

Area of Science:

• Reproductive Biology
• Cell Physiology
• Aquatic Animal Health

Background:

• Spermatozoon volume regulation is vital for male fertility across species.
• Aquaporins (AQPs) are implicated in mammalian sperm volume control.
• Marine teleost sperm face hypertonic shock upon ejaculation, requiring volume regulation.

Purpose of the Study:

• To investigate the presence and function of Aqp3a in gilthead seabream (Sparus aurata) spermatozoa.
• To determine the role of Aqp3a in regulating seabream sperm motility and flagellar morphology under hypertonic conditions.

Main Methods:

• Utilized a paralog-specific antibody to detect Aqp3a expression in seabream sperm.
• Employed an AQP3 antagonist (DFP00173) and a specific antibody (α-SaAqp3a) to inhibit Aqp3a function.
• Assessed sperm motility kinetics and analyzed sperm tail morphology using electron microscopy.

Main Results:

• Seabream sperm express Aqp3a, localized to the posterior flagellar region.
• Inhibition of Aqp3a impaired sperm motion kinetics post-activation but not initial motility.
• Aqp3a inhibition led to abnormal sperm tail morphologies, including swelling and coiling.

Conclusions:

• Aqp3a plays a conserved role as an osmosensor in fish spermatozoa.
• Aqp3a regulates post-activation cell volume by controlling water/solute efflux under hypertonic stress.
• Aqp3a is essential for maintaining normal sperm tail morphology and motility kinetics.