Sperm from the Calmegin-Deficient Mouse Have Normal Abilities for Binding and Fusion to the Egg Plasma Membrane

• Published in: Developmental biology Vol. 250; no. 2; pp. 348 - 357
• Main Authors: Yamagata, Kazuo, Nakanishi, Tomoko, Ikawa, Masahito, Yamaguchi, Ryou, Moss, Stuart B., Okabe, Masaru
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.10.2002
• Subjects: Acrosome - physiology; ADAM; ADAM Proteins; Animals; Calcium-Binding Proteins; calmegin; Calnexin - deficiency; Calnexin - genetics; Calnexin - physiology; Cell Membrane - physiology; chaperone; egg; Female; fertilin; Fertilins; fertilization; Green Fluorescent Proteins; In Vitro Techniques; Luminescent Proteins - metabolism; Male; Membrane Fusion - physiology; Membrane Glycoproteins - deficiency; Membrane Glycoproteins - physiology; Metalloendopeptidases - deficiency; Metalloendopeptidases - physiology; Mice; Mice, Knockout; Mice, Transgenic; Molecular Chaperones; piezo-micromanipulator; Recombinant Proteins - metabolism; sperm; Sperm-Ovum Interactions - physiology; Spermatozoa - physiology; zona pellucida; Zona Pellucida - physiology; fertilin; ADAM; chaperone; fertilization; egg; zona pellucida; sperm; piezo-micromanipulator; calmegin
• ISSN: 0012-1606; 1095-564X
• DOI: 10.1006/dbio.2002.0803

Calmegin is a putative testis-specific molecular chaperone required for the heterodimerization of fertilin α/β and the appearance of fertilin β on the sperm surface. Calmegin-deficient mice are almost completely sterile. The cause of the sterility initially was considered to be impaired abilities in sperm/zona pellucida (ZP) and sperm/egg plasma membrane (EPM) binding, and in the ascension of sperm to the oviduct, phenotypes similar to those seen in sperm from fertilin β-deficient animals. We have developed a new method in which eggs were prepared without any detectable ZP3 on their surfaces by using a piezo-driven micromanipulator. Using these eggs and sperm containing the green fluorescent protein in their acrosomes, which can distinguish acrosome-intact from acrosome-reacted sperm, the binding and fusing abilities of calmegin-deficient sperm were reexamined. Under these conditions, acrosome-reacted sperm retained their ability to bind to and fuse with the EPM. The reduction in EPM binding of sperm from the calmegin −/− animals was apparently due to the artifactual binding of large numbers of acrosome-intact sperm from calmegin +/− mice to ZP remnants remaining on the EPM prepared with acidic Tyrode's solution. Thus, the sperm defect in calmegin-null animals is not at the level of sperm–EPM binding but rather may involve either sperm–ZP binding and/or sperm transit to the oviduct. Because fertilin β is absent from calmegin-deficient mice, these results also suggest that the role of fertilin β in sperm–EPM interaction needs to be reevaluated.