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Mitochondria-cytoskeleton interactions in the sperm midpiece
1Department of Cell Biology, Vanderbilt University, Nashville, Tennessee 37232.
Abstract:
The mitochondrial sheath of mammalian spermatozoa is adherent to an underlying organized network of electron-dense material termed the submitochondrial reticulum (SMR). In this manuscript we further characterize the substructure of the SMR and the outer mitochondrial membrane and provide new information on their structural interaction. The SMR resists solubilization by detergent and once partially released from the midpiece of extracted spermatozoa, it appears in negatively stained preparations as a network of longitudinally oriented ribons of fibrillar material which are laterally interconnected. In detergent-extracted specimens the SMR remains attached to the outer mitochondrial membrane thereby suggesting a firm structural interaction. Negatively stained specimens also demonstrate that the outer mitochondrial membrane possesses a paracrystalline substructure and it is suggested that ordered arrays of membrane-associated proteins are involved in the structural interaction with the SMR. The potential roles of this cytoskeletal complex during spermiogenesis and in mature sperm are discussed.
Insights
The submitochondrial reticulum (SMR) is a stable network within sperm mitochondria. This study reveals its structural interaction with the outer mitochondrial membrane, suggesting a role in sperm function.
Area of Science:
- Cell Biology
- Spermatozoa Ultrastructure
- Mitochondrial Dynamics
Background:
- Mammalian spermatozoa possess a unique mitochondrial sheath surrounding the midpiece.
- The submitochondrial reticulum (SMR) is an electron-dense network associated with this sheath.
- Previous studies have not fully elucidated the SMR's structure and interaction with the mitochondria.
Purpose of the Study:
- To further characterize the substructure of the submitochondrial reticulum (SMR).
- To investigate the structural interaction between the SMR and the outer mitochondrial membrane.
- To explore the potential roles of this cytoskeletal complex in sperm development and function.
Main Methods:
- Detergent extraction of mammalian spermatozoa.
- Negative staining electron microscopy of extracted sperm components.
- Analysis of the SMR's resistance to solubilization.
- Microscopic examination of the SMR-outer mitochondrial membrane interface.
Main Results:
- The SMR is a detergent-resistant, fibrillar network interconnected laterally.
- The SMR remains attached to the outer mitochondrial membrane after extraction, indicating a strong interaction.
- The outer mitochondrial membrane exhibits a paracrystalline substructure.
- Ordered membrane-associated proteins likely mediate the interaction between the SMR and the outer mitochondrial membrane.
Conclusions:
- The submitochondrial reticulum (SMR) forms a stable cytoskeletal complex with the sperm outer mitochondrial membrane.
- This interaction is mediated by specific protein structures within the mitochondrial membrane.
- The SMR-outer mitochondrial membrane complex may play a crucial role in sperm morphology and function during spermiogenesis and in mature sperm.