Preimplantation mouse embryos express a cell surface receptor for tissue-plasminogen activator

Area of Science:

• Reproductive biology
• Developmental biology
• Biochemistry

Background:

• Tissue-plasminogen activator (t-PA) is a serine protease.
• t-PA has been observed intracellularly in oocytes and extracellularly in fertilized eggs.

Purpose of the Study:

• To investigate the source and nature of extracellular t-PA activity in preimplantation mouse embryos.
• To determine if embryos synthesize t-PA or bind it from the environment.

Main Methods:

• Analysis of t-PA activity in preimplantation embryos at different stages (2-cell, 4-cell, morula).
• Culturing morulae and assessing their ability to bind exogenous mouse t-PA.
• Northern blot analysis to detect t-PA mRNA in embryos.
• Testing binding specificity with urokinase-type plasminogen activator (u-PA) and human t-PA.

Main Results:

• Extracellular t-PA activity is bound to the surface of fertilized eggs.
• t-PA activity levels change during preimplantation development, peaking at the morula stage.
• Cultured morulae lack endogenous t-PA activity but can bind exogenous mouse t-PA.
• Preimplantation embryos do not express detectable t-PA mRNA.
• Binding is specific to mouse t-PA, dose-dependent, saturable, and does not require the active site.

Conclusions:

• The t-PA activity associated with preimplantation mouse embryos originates from the oviductal fluid, not embryonic synthesis.
• A specific t-PA-binding activity exists on the surface of preimplantation mouse embryos.
• This binding may localize and concentrate t-PA activity, influencing early embryonic development.