Sperm from the calmegin-deficient mouse have normal abilities for binding and fusion to the egg plasma membrane.
Calmegin is a putative testis-specific molecular chaperone required for the heterodimerization of fertilin alpha/beta and the appearance of fertilin beta 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 beta-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 beta is absent from calmegin-deficient mice, these results also suggest that the role of fertilin beta in sperm-EPM interaction needs to be reevaluated.
Yamagata
Kazuo
K
Genome Information Research Center, Osaka University, Yamadaoka 3-1, Suita, Osaka, 565-0871 Japan.
Nakanishi
Tomoko
T
Ikawa
Masahito
M
Yamaguchi
Ryou
R
Moss
Stuart B
SB
Okabe
Masaru
M
D051722:ADAM Proteins; D000177:Acrosome / Q000502:physiology; D000818:Animals; D002135:Calcium-Binding Proteins; D037281:Calnexin / Q000172:deficiency* / Q000235:genetics / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology; D005260:Female; D000072196:Fertilins; D049452:Green Fluorescent Proteins; D066298:In Vitro Techniques; D008164:Luminescent Proteins / Q000378:metabolism; D008297:Male; D008561:Membrane Fusion / Q000502:physiology; D008562:Membrane Glycoproteins / Q000172:deficiency / Q000502:physiology; D008666:Metalloendopeptidases / Q000172:deficiency / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D018832:Molecular Chaperones; D011994:Recombinant Proteins / Q000378:metabolism; D013084:Sperm-Ovum Interactions / Q000502:physiology*; D013094:Spermatozoa / Q000502:physiology*; D015044:Zona Pellucida / Q000502:physiology
D002135:Calcium-Binding Proteins; D008164:Luminescent Proteins; D008562:Membrane Glycoproteins; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D037281:Calnexin; D049452:Green Fluorescent Proteins; C087341:calmegin; D051722:ADAM Proteins; C000606455:Adam1a protein, mouse; C000606458:Adam2 protein, mouse; D000072196:Fertilins; D008666:Metalloendopeptidases