A CatSper-Uninvolved Mechanism to Induce Forward Sperm Motility in the Internal Fertilization

Area of Science:

• Reproductive Biology
• Sperm Physiology
• Molecular Signaling

Background:

• Sperm motility is crucial for fertilization and often regulated by ion channels and exchangers like CatSper, sNHE, and sAC.
• Some species have lost key components of these signaling pathways, necessitating investigation into alternative mechanisms.
• The internally fertilizing newt, Cynops pyrrhogaster, provides a model to study CatSper-independent sperm motility regulation.

Purpose of the Study:

• To investigate the signaling pathways controlling sperm tail undulating membrane undulation in Cynops pyrrhogaster, independent of CatSper.
• To elucidate the role of intracellular pH regulation and cyclic AMP in initiating sperm motility.

Main Methods:

• Reverse-transcription PCR was used to detect gene expression (sNHE).
• Sperm were exposed to varying extracellular pH, egg jelly extract, and specific inhibitors (DIDS, KH7, DDA, H89, RN1747) and activators (dibutyryl cyclic AMP).
• Changes in sperm cytoplasmic pH and cyclic AMP concentration were measured, and sperm motility (undulating membrane undulation) was assessed.

Main Results:

• sNHE was not detected in newt sperm; however, intracellular pH increased in high extracellular pH conditions.
• Bicarbonate transport, potentially via carbonic anhydrase and SLC4 transporters, and soluble adenylyl cyclase (sAC) activity were implicated in raising intracellular pH and cyclic AMP levels.
• Inhibitors of sAC (KH7), protein kinase A (PKA; H89), and transient receptor potential (TRP) channels (RN1747) significantly weakened sperm undulation, while bicarbonate enhanced it.

Conclusions:

• The high pH of egg jelly initiates a signaling cascade involving sAC, PKA, and TRP channels in newt sperm.
• This pathway, coacting with sperm motility-initiating substance (SMIS), regulates the undulating membrane for vigorous forward motility.
• These findings highlight a CatSper-independent mechanism for sperm motility control in this species.