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Questions and Answers
Which step in mammalian fertilization involves the breakdown of the barrier to the egg by proteolytic enzymes?
The slow block to polyspermy is an immediate response following fertilization.
False
Match the following components of fertilization with their corresponding functions:
Ovastacin = Protease found in cortical granules that prevents polyspermy Calcium release = Triggers egg activation and developmental processes Zinc spark = Involves a release of zinc ions during fertilization Juno = Protein on the egg surface that recognizes sperm
What is one method sea urchins use to prevent fertilization by sperm from other species?
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The mechanism of fast block to polyspermy is common among all types of fertilization.
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Match the following peptides with their respective species:
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What happens to the membrane potential of sea urchin eggs after fertilization?
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Species-specific binding of the acrosomal process is crucial for successful fertilization in sea urchins.
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What is the primary role of the protein Ovastacin in mammalian fertilization?
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During which step of mammalian fertilization do sperm sense and follow chemical gradients?
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What is the significance of the 'zinc spark' in the fertilization process?
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Which component is essential for the recognition of sperm by the mouse zona pellucida?
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What is the role of calcium release across a sea urchin egg during fertilization?
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What role does the peptide Resact play in sea urchin fertilization?
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Which mechanism primarily prevents multiple sperm from fertilizing a sea urchin egg?
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How do species-specific sperm-egg interactions occur during the fertilization process?
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What is the major function of sulfated polysaccharides in the egg jelly coat?
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Which of the following correctly describes the diameter of both sea urchin and mammalian eggs?
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What is the consequence of a dispermic fertilization in sea urchins?
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Which environmental cues are likely involved in the broadcast spawning process?
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Which of the following statements about the acrosome reaction is true?
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Study Notes
Sea Urchin & Mammal Egg Structure
- Both sea urchin and mammalian eggs are approximately 100 micrometers in diameter.
- Sea urchin eggs are released into the external environment where fertilization occurs.
- Mammalian eggs are fertilized internally within the female reproductive tract.
Sea Urchin Fertilization
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Sperm Chemotaxis: Sea urchin sperm are attracted to the egg by a chemical gradient of chemoattractants.
- Resact and Speract are small peptides that act as chemoattractants for sea urchin sperm.
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Species-Specific Acrosome Reaction: The acrosomal reaction in sea urchin sperm is triggered by species-specific sulfated polysaccharides present in the egg jelly coat.
- The acrosome reaction exposes a binding protein that allows sperm to bind to the egg surface.
- Species-Specific Binding: The acrosomal process of the sperm binds to species-specific receptors on the egg surface.
- Fast Block to Polyspermy: Sea urchin eggs exhibit a rapid change in membrane potential, preventing further sperm from entering.
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Slow Block to Polyspermy: The fertilization envelope forms, hardening the egg surface and preventing sperm from binding.
- The cortical granules in the egg release enzymes that trigger the formation of the fertilization envelope.
- Udx1, a calcium-dependent dual oxidase, is essential for the formation of the fertilization envelope.
Mammalian Fertilization
- Capacitation: Sperm undergo changes in the female reproductive tract that enable them to fertilize the egg.
- Sperm Chemotaxis: Mammalian sperm follow gradients of thermal and chemical cues, particularly progesterone.
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Acrosome Reaction: Mammalian sperm undergo the acrosome reaction upon binding to the zona pellucida of the egg.
- Acrosomal proteases break down the zona pellucida, allowing sperm to reach the egg plasma membrane.
- Sperm-Egg Fusion: Izumo on the sperm surface binds to Juno on the egg surface, facilitating fusion of the sperm and egg plasma membranes.
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Block to Polyspermy:
- Ovastacin, a protease found in cortical granules, cleaves ZP2 in the zona pellucida, blocking further sperm entry.
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Zinc Spark: During fertilization, a sudden release of zinc ions occurs, visualized as a spark.
- This "zinc spark" may be involved in preventing polyspermy.
Pronuclear Movements
- After fertilization, the sperm and egg nuclei, known as pronuclei, move towards each other and fuse.
- The fusion of pronuclei restores the diploid number of chromosomes and initiates development.
Sea Urchin Egg Structure
- Sea urchin eggs are approximately 100 mm in diameter.
- Sperm chemotaxis - movement toward the egg - is dependent on chemoattractant peptides like Resact and Speract.
- Resact is a 14 amino acid peptide made by the sea urchin Arbacia.
- Speract is a 14 amino acid peptide made by the sea urchin Strongylocentrotus.
- RGC (receptor guanylyl cyclase) acts as a receptor for chemoattractant peptides on the sperm.
- Sperm-egg interactions are species-specific.
- The acrosome reaction is triggered by sulfated polysaccharides in the egg jelly coat - this is species specific.
- The species-specific acrosomal process binds to the egg surface.
- The sperm and egg plasma membranes fuse externally.
- Dispermy - fertilization with multiple sperm - is a problem in sea urchin fertilization, leading to aberrant development.
- The fast block to polyspermy involves a rapid change in the membrane potential of the egg after fertilization.
- The slow block to polyspermy involves the formation of the fertilization envelope, which is a barrier that prevents further sperm entry.
- Cortical granules release their contents - including enzymes and proteins - into the space between the egg plasma membrane and the vitelline membrane to form the fertilization envelope.
- Udx1 is a calcium-dependent dual oxidase crucial in this process.
- Calcium release from the endoplasmic reticulum is essential for egg activation.
- Inositol phosphates are vital for calcium release from the endoplasmic reticulum.
Mammalian Egg Structure
- Mammalian eggs undergo a process called capacitation before they can fertilize.
- Capacitation involves changes to the sperm that increase its ability to bind to the egg.
- Sperm use thermal gradient and chemical signals (e.g., progesterone) to track down the egg.
- The acrosome reaction in mammals is triggered by the zona pellucida, which is a layer surrounding mammalian eggs.
- The acrosome reaction releases proteolytic enzymes that break down the zona pellucida, facilitating fertilization.
- Izumo protein on the sperm and Juno protein on the egg mediate the fusion of their membranes.
- The block to polyspermy in mammals occurs due to the cleavage of ZP2, a protein in the zona pellucida.
- The cleavage of ZP2 is mediated by ovastacin - a protease found in cortical granules.
- The "zinc spark" occurs upon fertilization.
- The zinc spark is a burst of zinc ions released from the egg, which can be visualized in real-time.
- During fertilization, the male and female pronuclei move towards each other and eventually fuse.
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Description
Test your knowledge on the structure and fertilization processes of sea urchin and mammalian eggs. This quiz covers key concepts such as sperm chemotaxis, acrosome reactions, and polyspermy prevention mechanisms. Understand the differences between external and internal fertilization as you explore these fascinating reproductive strategies.
