Proteases stimulate fertilization-like responses in starfish eggs

Area of Science:

• Marine Biology
• Developmental Biology
• Cellular Biology

Background:

• Egg activation at fertilization involves complex cellular events.
• The precise molecular mechanisms initiating these events are not fully understood.

Purpose of the Study:

• To investigate the role of proteases in initiating starfish egg activation.
• To identify potential extracellular receptors involved in fertilization.

Main Methods:

• Starfish eggs (Asterina miniata) were exposed to various proteases (trypsin, chymotrypsin, pronase, kallikrein, recombinant trypsin).
• Cortical granule exocytosis was measured using FM 1-43 fluorescence.
• Intracellular calcium levels were monitored using calcium green dextran.
• DNA synthesis was assessed by bromodeoxyuridine incorporation.

Main Results:

• Proteases like trypsin, chymotrypsin, and pronase rapidly induced cortical granule exocytosis and fertilization envelope elevation.
• These proteases also increased intracellular calcium and stimulated DNA synthesis.
• Exocytosis occurred even in low external calcium conditions, ruling out simple egg damage.
• A non-proteolytic mutant trypsin did not induce these responses.

Conclusions:

• Proteolytic cleavage of an extracellularly exposed protein can trigger fertilization-like responses in starfish eggs.
• This protein may function as a receptor that initiates egg activation upon sperm binding.
• This finding provides insights into the molecular signaling pathways of fertilization.