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Epididymal SPAM1 Is a Marker for Sperm Maturation in the Mouse¹

Department of Biological Sciences, University of Delaware, Newark, Delaware 19716

ABSTRACT

Sperm adhesion molecule 1 (SPAM1), is a glycosyl phoshatidylinositol-linked sperm membrane protein that is dually expressed in testis and epididymis. Epididymal SPAM1 is secreted in all three regions of the epididymis in all mammalian species studied, including humans. It shares the same molecular mass and neutral hyaluronidase activity as the testicular and sperm isoforms that are responsible for the penetration of the cumulus during fertilization. Using wild-type (W/T) sperm and those from mice homozygous for either a null (Spam1–/–) or mutant Spam1 allele, which results in decreased mRNA and protein, we demonstrate that sperm binding of epididymal SPAM1 occurs in vitro after exposure to W/T sperm-free epididymal luminal fluid (ELF). Binding or adsorption that occurred after incubation at room temperature or 32°C was detected immunocytochemically and confirmed quantitatively using flow cytometry. The localization of SPAM1 on the plasma membrane of Spam1-null sperm mimicked that seen in the W/T. The remarkable increase in binding on W/T caudal sperm indicates that they are not fully saturated with SPAM1 during storage, and suggests that uptake of epididymal SPAM1 in vivo augments testicular SPAM1. Spam1-null sperm exposed to W/T ELF for 45–60 min during in vitro capacitation to allow epididymal SPAM1 binding showed a highly significant (P < 0.001) increase in cumulus penetration after 6–7 h compared to those incubated in ELF from null males. Similarly, the number of cumulus-free oocytes was also highly significantly greater (P < 0.001) than that for sperm capacitated in W/T SPAM1-antibody-inhibited ELF. Because epididymal SPAM1 uptake significantly increases cumulus penetration, we conclude that it is a marker of sperm maturation.

epididymal luminal fluid, epididymis, GPI anchor, in vitro fertilization, male reproductive tract, secretory protein, Spam1-null sperm, sperm capacitation, sperm hyaluronidase activity, sperm maturation

¹ Supported by National Institutes of Health grant RO1 HD38373 to P.A.M-D.

² Correspondence: Patricia A. Martin-DeLeon, Department of Biological Sciences, University of Delaware, Newark, DE 19716. FAX: 302 831 2281; pdeleon{at}udel.edu

This article has been cited by other articles:

				G. S Griffiths, K. A Miller, D. S Galileo, and P. A Martin-DeLeon Murine SPAM1 is secreted by the estrous uterus and oviduct in a form that can bind to sperm during capacitation: acquisition enhances hyaluronic acid-binding ability and cumulus dispersal efficiency Reproduction, March 1, 2008; 135(3): 293 - 301. [Abstract] [Full Text] [PDF]

				K. A. Miller, M. Shao, and P. A. Martin-Deleon Hyalp1 in Murine Sperm Function: Evidence for Unique and Overlapping Functions With Other Reproductive Hyaluronidases J Androl, January 1, 2007; 28(1): 67 - 76. [Abstract] [Full Text] [PDF]