Sperm surface galactosyltransferase activities during in vitro capacitation

Area of Science:

• Reproductive Biology
• Glycobiology
• Cell Biology

Background:

• Sperm surface galactosyltransferases are implicated in fertilization.
• Binding to egg zona pellucida N-acetylglucosamine (GlcNAc) residues is a key step.

Purpose of the Study:

• To investigate sperm surface galactosyltransferase activity during in vitro capacitation.
• To correlate changes in enzymatic activity with fertilizing ability.

Main Methods:

• Examined sperm surface galactosyltransferase activity during in vitro capacitation.
• Utilized Ca(++)-containing and Ca(++)-free media for capacitation.
• Tested inhibition by pronase-digested polyactosaminyl glycosides.

Main Results:

• Uncapacitated sperm show galactosyltransferases loaded with poly N-acetyllactosamine substrates.
• Capacitation releases these substrates, exposing galactosyltransferases for zona pellucida binding.
• High molecular weight polyactosaminyl glycosides act as decapacitation factors by inhibiting sperm-egg binding.

Conclusions:

• Sperm capacitation involves the release of inhibitory substrates from surface galactosyltransferases.
• Decapacitation factors, identified as polyactosaminyl glycosides, compete with the zona pellucida for sperm galactosyltransferase binding.
• This defines a molecular mechanism for sperm capacitation and egg- zona pellucida interaction.