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Generation of a mouse sperm membrane fraction with zona receptor activity
1Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710.
Abstract:
To identify mouse sperm components involved in primary sperm binding to zonae pellucidae, a mouse sperm plasma membrane-enriched fraction was generated using a vortex method. The crude membrane fraction recovered after vortexing was resolved into three bands and a pellet by centrifugation on a discontinuous sucrose gradient. Ultrastructural analysis indicated that Bands 2 and 3 were composed predominantly of membranes, although Band 3 was contaminated with mitochondria; Band 1 and the gradient pellet contained insufficient material and were unsuitable for ultrastructural analysis. To determine where plasma membranes migrate in the gradient, sperm were labeled vectorially with 125I; subsequently, membrane fractions were analyzed by SDS-PAGE and autoradiography. Band 2 was enriched threefold in radiolabel when compared with Band 3. Examination of intact and vortexed sperm stained with regionally distributed anti-mouse sperm monoclonal antibodies revealed that vortexing removed anterior head plasma membrane preferentially. Bioactivity, defined as the ability to inhibit primary sperm binding to the zona pellucida in a concentration-dependent manner, was contained in the crude membrane fraction and Band 2 exclusively, with inhibition of 53% and 44%, respectively, at the maximum concentration tested. Band 3 exhibited no significant bioactivity. We conclude from these results that a plasma membrane-enriched fraction, Band 2, isolated from mouse cauda epididymal sperm, exhibits zona pellucida receptor activity.
Insights
Researchers identified key mouse sperm plasma membrane components responsible for binding to the zona pellucida. Fraction Band 2, enriched in plasma membranes, demonstrated significant zona pellucida receptor activity, inhibiting sperm-zona binding.
Area of Science:
- Reproductive Biology
- Sperm-egg Interaction
- Cellular Membrane Research
Background:
- Primary sperm binding to the zona pellucida is a critical step in fertilization.
- Identifying specific sperm components involved in this interaction is essential for understanding reproductive processes.
- Previous studies have suggested the involvement of sperm plasma membranes in zona pellucida binding.
Purpose of the Study:
- To isolate and characterize mouse sperm plasma membrane fractions involved in primary binding to the zona pellucida.
- To determine the specific location of zona pellucida receptor activity within the sperm plasma membrane.
Main Methods:
- Generation of a mouse sperm plasma membrane-enriched fraction using a vortex method.
- Separation of the membrane fraction using discontinuous sucrose gradient centrifugation.
- Analysis of membrane composition via ultrastructural analysis, SDS-PAGE, and autoradiography after vectorial radiolabeling.
- Assessment of bioactivity by measuring inhibition of primary sperm binding to the zona pellucida.
Main Results:
- Sucrose gradient centrifugation yielded three bands and a pellet; Band 2 was predominantly plasma membrane.
- Vectorial labeling and SDS-PAGE confirmed Band 2 was enriched in plasma membrane components.
- The plasma membrane-enriched fraction (crude) and Band 2 exhibited significant bioactivity, inhibiting sperm-zona binding by 53% and 44%, respectively.
- Band 3 showed no significant bioactivity, indicating zona pellucida receptor activity is localized to Band 2.
Conclusions:
- A plasma membrane-enriched fraction (Band 2) isolated from mouse cauda epididymal sperm possesses zona pellucida receptor activity.
- These findings identify specific sperm plasma membrane components crucial for the initial binding event during fertilization.
- The study provides a method for isolating functionally active sperm membrane domains involved in gamete recognition.