Receptor function of mouse sperm surface galactosyltransferase during fertilization

Area of Science:

• Reproductive biology
• Biochemistry
• Cell biology

Background:

• Previous research suggested sperm galactosyltransferase (GalTase) mediates mouse sperm-egg binding.
• This interaction involves GalTase recognizing N-acetylglucosamine (GlcNAc) on the zona pellucida.

Purpose of the Study:

• To provide direct evidence supporting the GalTase-mediated mechanism of gamete binding.
• To investigate the role of GalTase conformation and enzymatic activity in sperm-zona pellucida interactions.

Main Methods:

• Purification of sperm GalTase using sequential affinity chromatography.
• Assessing the effect of purified GalTase on sperm binding to the zona pellucida.
• Utilizing UDP-galactose (UDPGal) and UDP-glucose to study GalTase-zona interactions.
• Employing anti-GalTase antibodies to inhibit sperm-zona binding.
• Indirect immunofluorescence to localize sperm GalTase.

Main Results:

• Purified, native GalTase dose-dependently inhibited sperm binding to the zona pellucida.
• Heat-inactivated or Mn++-deficient GalTase did not inhibit binding, indicating the need for native conformation and enzymatic activity.
• UDPGal, but not UDP-glucose, inhibited sperm binding and dissociated existing adhesions by releasing GalTase from GlcNAc.
• Anti-GalTase IgG and Fab fragments inhibited sperm binding and blocked GalTase activity.
• Immunofluorescence localized GalTase to the dorsal anterior sperm head.

Conclusions:

• Sperm galactosyltransferase (GalTase) is confirmed as a principal receptor mediating mouse sperm binding to the egg zona pellucida.
• The enzymatic activity and native conformation of GalTase are essential for gamete recognition and binding.
• UDPGal can disrupt sperm-zona adhesions by releasing GalTase, highlighting the dynamic nature of this interaction.