Journal of Andrology
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Published-Ahead-of-Print September 10, 2009, DOI:10.2164/jandrol.109.007880

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Bactericidal/Permeability-Increasing Protein (BPI) Is Associated with the Acrosome Region of Rodent Epididymal Spermatozoa

Rieko Yano , Takuya Matsuyama , Takane Kaneko , Hitoshi Kurio , Emi Murayama , Kiyotaka Toshimori , and Hiroshi Iida *

* To whom correspondence should be addressed. E-mail: iidahiro{at}agr.kyushu-u.ac.jp.

To elucidate the molecular mechanisms involved in sperm maturation during epididymal transit, we intended to isolate secretory molecules that are region-specifically expressed along the epididymis and secreted into the lumen of epididymal ducts. By using differential display screening and DNA sequence analyses, we isolated a rat bactericidal/permeability- increasing protein (BPI) possessing a signal sequence at its N-terminal, which was expressed in caput region of epididymis but not in caudal region. RT-PCR analysis and in situ hybridization showed that rat BPI mRNA was highly expressed in caput epididymal epithelium and that its expression level was developmentally up-regulated. Confocal laser scanning microscopy with the anti-BPI antibody revealed that in both rats and mice, BPI protein was detected on granule-like structures in the lumen of both caput and cauda epididymal ducts as well as at the sperm surface covering the acrosome region in spermatozoa freshly isolated from epididymis. Acrosome reaction induced by calcium ionophore A23187 in vitro brought about disappearance of BPI on mouse spermatozoa. These data suggested that BPI, which is synthesized in caput epididymis and secreted into the lumen, is associated with not only the granule-like structures but also the sperm surface covering the acrosome region and that BPI bound to the acrosome region is extinguished by acrosome reaction. There is a possibility that BPI bound to the sperm surface covering the acrosome region in rodent spermatozoa might be involved in sperm maturation or fertilization.


Key words: Epididymis • Fertilization • Reproductive Tract • Sperm • Testis






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