Sperm Chemotaxis and Acrosome Reaction Mechanisms
Summary
Sperm chemotaxis and the acrosome reaction constitute two critical processes that ensure fertilisation across a broad range of species. Chemotaxis refers to the guided movement of spermatozoa along chemical gradients released by the egg or its surrounding structures. This directional navigation relies on the transduction of external cues into intracellular signalling events—principally changes in cyclic nucleotides and Ca2+ concentration—that modulate the flagellar beat pattern, enabling sperm to steer towards the egg. Upon reaching the vicinity of the egg, the acrosome reaction is triggered: a Ca2+-dependent exocytotic event in which the outer acrosomal membrane fuses with the plasma membrane of the sperm head, releasing enzymes that facilitate penetration of the zona pellucida or chorion. Integration of chemotactic steering and timely acrosomal exocytosis is essential to achieve species-specific recognition, prevent polyspermy and ensure high fertilisation efficiency. Recent advances have clarified the molecular identity and interplay of ion channels, receptors and second-messenger enzymes that underlie these processes, revealing both conserved principles and species-specific adaptations. Understanding these mechanisms offers potential applications in assisted reproduction, contraception and the management of fertility disorders by targeting key molecular players in sperm guidance and activation.
Research from Nature Portfolio
Recent studies have elucidated how sperm navigate three-dimensional chemical landscapes by alternating between helical swimming and sharp turning manoeuvres in response to fluctuating chemoattractant levels. In the sea urchin model, sperm were shown to employ periodic Ca2+ signals during helical swimming to gradually align their trajectories with the gradient, while rapid klinotactic turns are initiated by decreases in cyclic GMP and membrane voltage. Complementary computational modelling of sea urchin flagellar signalling has identified the CatSper channel as the principal generator of intracellular Ca2+ oscillations that drive these steering behaviours, with other Ca2+ channels playing supporting roles. In ascidian sperm, binding of a sperm-activating peptide to a plasma membrane Ca2+-ATPase has been demonstrated to enhance Ca2+ efflux, finely tuning intracellular Ca2+ dynamics and flagellar waveform conversion, thereby guiding chemotactic turns with high precision.
Sperm Chemotaxis and Acrosome Reaction Mechanisms publication trend
The graph below shows the total number of articles in sperm chemotaxis and acrosome reaction mechanisms across all publications each year (not limited to Nature Index journals).
Technical terms
Chemotaxis: Directed movement of sperm along a chemical gradient towards the egg.
Acrosome reaction: Ca2+-dependent exocytosis in the sperm head that releases enzymes for zona pellucida penetration.
Chemoattractant: Molecule released by the egg or its surroundings that forms a concentration gradient guiding sperm.
CatSper channel: Sperm-specific, pH- and voltage-sensitive Ca2+ channel essential for generating intracellular Ca2+ oscillations during chemotaxis.
Plasma membrane Ca2+-ATPase (PMCA): Enzyme that extrudes Ca2+ from the sperm cytoplasm, modulating flagellar waveform and steering.
cAMP: Cyclic adenosine monophosphate, a second messenger that regulates protein phosphorylation and flagellar motility activation.
References
- Spawning-Induced pH Increase Activates Sperm Attraction and Fertilization Abilities in Eggs of the Ascidian, Phallusia philippinensis and Ciona intestinalis. International Journal of Molecular Sciences (2023).
- Sperm navigation along helical paths in 3D chemoattractant landscapes. Nature Communications (2015).
- Network model predicts that CatSper is the main Ca2+ channel in the regulation of sea urchin sperm motility. Scientific Reports (2017).
- Ca2+ efflux via plasma membrane Ca2+-ATPase mediates chemotaxis in ascidian sperm. Scientific Reports (2018).
- Distinct Roles of Soluble and Transmembrane Adenylyl Cyclases in the Regulation of Flagellar Motility in Ciona Sperm. International Journal of Molecular Sciences (2014).
- Sperm chemotaxis is driven by the slope of the chemoattractant concentration field. eLife (2020).
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