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Identification of the Molecular Chaperone, Heat Shock Protein 1 (Chaperonin 10), in the Reproductive Tract and in Capacitating Spermatozoa in the Male Mouse¹

Reproductive Science Group⁴ and Australian Research Council (ARC) Centre of Excellence in Biotechnology and Development,⁵ School of Environmental and Life Sciences, University of Newcastle, Callaghan, New South Wales 2308, Australia Monash Institute of Medical Research and ARC Centre of Excellence in Biotechnology and Development,⁶ Monash University, Victoria 3168, Australia

ABSTRACT

Mammalian spermatozoa must undergo epididymal maturation in the male reproductive tract and capacitation in the female tract before acquiring the ability to fertilize an oocyte. Previous studies from our laboratory have demonstrated a causal relationship between capacitation-associated surface phosphotyrosine expression and the ability of mouse spermatozoa to recognize the oocyte and engage in sperm-zona pellucida interaction. Our previous analyses of the surface phosphoproteome of capacitated murine spermatozoa identified two molecular chaperones, heat shock protein (HSP) D1 and HSP90B1, with well-characterized roles in protein folding and the assemblage of multimeric protein complexes. The expression of these chaperones was restricted to the rostral aspect of the sperm head, in an ideal position to mediate sperm-zona pellucida interaction. Herein, we report the characterization of an additional chaperone in this location, HSPE1 (chaperonin 10; HSP10). This chaperone was identified using a coimmunoprecipitation strategy employing HSPD1 as bait. The putative interaction between HSPE1 and HSPD1 was supported by reciprocal immunoprecipitation and colocalization studies, which demonstrated the coordinated appearance of both proteins on the surface of the sperm head during capacitation. However, the surface exposure of the protein was lost upon induction of acrosomal exocytosis, as would be expected of a protein potentially involved in sperm-zona pellucida interaction. Collectively, these data invite speculation that a number of molecular chaperones are involved in modification of the sperm surface during capacitation to render these cells functionally competent to engage the process of fertilization.

gamete biology, sperm, sperm capacitation, sperm maturation

³These authors contributed equally to this work.

¹Supported by the ARC Centre of Excellence in Biotechnology and Development and the National Health and Medical Research Council of Australia.

Correspondence: ²Brett Nixon, ARC Centre of Excellence in Biotechnology and Development, School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia. FAX: 61 2 4921 6923; e-mail: brett.nixon{at}newcastle.edu.au