The putative chaperone calmegin is required for sperm fertility

Masahito Ikawa, Ikuo Wada, Katsuya Kominami, Daisuke Watanabe, Kiyotaka Toshimori, Yoshitake Nishimune and Masaru Okabe ()
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Masahito Ikawa: Research Institute for Microbial Diseases, Osaka University
Ikuo Wada: Sapporo Medical University School of Medicine
Katsuya Kominami: Research Institute for Microbial Diseases, Osaka University
Daisuke Watanabe: Research Institute for Microbial Diseases, Osaka University
Kiyotaka Toshimori: Medical College of Miyazaki
Yoshitake Nishimune: Research Institute for Microbial Diseases, Osaka University
Masaru Okabe: Research Institute for Microbial Diseases, Osaka University

Nature, 1997, vol. 387, issue 6633, 607-611

Abstract: Abstract The proper folding of newly synthesized membrane proteins in the endoplasmic reticulum (ER) is required for the formation of functional mature proteins. Calnexin is a ubiquitous ER chaperone that plays a major role in quality control by retaining incompletely folded or misfolded proteins1,2,3,4,5. In contrast to other known chaperones such as heat-shock proteins, BiP and calreticulin, calnexin is an integral membrane protein1,6. Calmegin is a testis-specific ER protein that is homologous to calnexin7,8,9. Here we show that calmegin binds to nascent polypeptides during spermatogenesis, and have analysed its physiological function by targeted disruption of its gene. Homozygous-null male mice are nearly sterile even though spermatogenesis is morphologically normal and mating is normal. In vitro, sperm from homozygous-null males do not adhere to the egg extracellular matrix (zona pellucida), and this defect may explain the observed infertility. These results suggest that calmegin functions as a chaperone for one or more sperm surface proteins that mediate the interactions between sperm and egg. The defective zona pellucida-adhesion phenotype of sperm from calmegin-deficient mice is reminiscent of certain cases of unexplained infertility in human males.

Date: 1997
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DOI: 10.1038/42484

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