Mammalian sperm develop their fertilizing ability through sperm capacitation within the female reproductive tract. While seminal vesicle secretions form the primary part of seminal plasma their presence prevents sperm capacitation (capacitation inhibition) and diminishes the fertility of already capacitated sperm (capacitation incapacitation). The Seminal Vesicle Secretion (SVS) protein family represents proteins that male mammals mainly release from their seminal vesicles. Semen contains high levels of certain proteins that significantly influence sperm function and reproductive success while facilitating gamete interaction particularly in rodents like mice and rats. SVS3 and SVS4 collaborate with SVS2 during sperm capacitation in the Seminal Vesicle Secretion (SVS) protein family but show less binding strength to GM1 compared to SVS2.
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Main Functions of SVS Proteins
Sperm Protection
SVS proteins can bind to sperm to form a protective layer to prevent immune system recognition. For example, SVS2 can protect sperm from being destroyed by the aggressive immune environment of the female reproductive tract.
Sperm Plug Formation
In rodents, a "sperm plug" can be formed after mating to prevent other males from mating, thereby increasing their own reproductive success rate. Proteins such as SVS1 and SVS2 are involved in the formation of the gel structure of this sperm plug.
Regulating Sperm Activity
Some SVS proteins may be involved in activating or inhibiting the activity of sperm and regulating it to enter the egg at the right time.
Antibacterial Defense
SVS proteins contained in semen have certain antibacterial effects and protect sperm from infection.
What is Sperm "Capacitation"?
Sperm capacitation describes how sperm develop fertilization competency through physiological and molecular changes after entering the female reproductive tract. Sperm capacitation occurs in the female reproductive tract after ejaculation, and its characteristic changes are: During sperm capacitation the flagella movement becomes a high-amplitude swing while sperm membranes.
Introduction to the SVS Protein Family
The SVS (Seminal Vesicle Secretion) protein family is a class of seminal plasma proteins secreted by the seminal vesicles of male mice, mainly including:
| Protein name |
Coding genes |
Functional description |
| SVS2 |
Svs2 |
Sperm protection, preventing premature capacitation |
| SVS3 |
Svs3a, Svs3b |
Antibacterial function, regulating uterine environment |
| SVS4 |
Svs4 |
This component could play a role in maintaining sperm membrane stability and facilitating sperm-egg interaction |
These proteins mix with sperm during ejaculation to form a protective coating.
Fig 1. Model of the action of the SVS family on sperm (Araki, N., et al. 2016).
Mechanism of Action of the SVS Protein Family in Sperm Capacitation
SVS2: Prevent premature sperm capacitation and protect sperm structure
- Binding to sperm membrane: The SVS2 protein connects to the sperm plasma membrane and both conserves membrane cholesterol while also postponing membrane fluidity shifts.
- Inhibits the start of capacitation: The SVS2 molecule maintains membrane stability which blocks sperm from experiencing premature capacitation within the vas deferens or the seminal vesicle.
- Protective function: Protects the sperm membrane from damage caused by reactive oxygen species and immune system attacks.
SVS3: Regulates immune response and microbial environment, indirectly promoting sperm capacitation
- Antibacterial function: SVS3 contains a defensive peptide-like structure that can inhibit bacterial infection in the vagina or uterus.
- Regulates the uterine immune environment: affects the tolerance of the female immune system to sperm, which is beneficial to sperm survival and capacitation.
SVS4: Assists in membrane stabilization and sperm-egg interaction
- Promotes fertilization process: May be involved in regulating membrane changes during sperm recognition and binding in the zona pellucida.
Clinical and Research Significance
- Assisted reproduction: Understanding SVS protein may help improve in vitro sperm processing techniques, such as in vitro capacitation and cryoprotection.
- Male infertility research: Abnormal expression of SVS protein may be the underlying molecular mechanism of some infertility cases.
- Contraceptive target: It can be used as a potential target for the development of non-hormonal male contraceptive drugs.
The Seminal Vesicle Secretory Protein Family Inhibits Sperm Motility and Capacitation
SVS2 SVS3 SVS4 seminal vesicle family proteins enable fertilization-ready sperm through regulation of capacitation using various methods to stabilize sperm membranes together with managing reproductive tract immunity and capacitation sequence. The seminal vesicle protein family secreted by humans functions to suppress sperm motility alongside preventing capacitation. SVS3 and SVS4 function in sperm capacitation while other decapacitation factors present in the male reproductive tract and seminal plasma may also exist. Research does not show if these factors stay active inside the body yet sperm must suppress their effects to gain fertilization capability.
References
- Araki, N., et al. Seminal vesicle proteins SVS3 and SVS4 facilitate SVS2 effect on sperm capacitation. Reproduction. 2016, 152(4): 313-21.
- Shindo, M., et al. Deletion of a seminal gene cluster reinforces a crucial role of SVS2 in male fertility. International Journal of Molecular Sciences. 2019, 20(18): 4557.
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