A STUDY OF THE MECHANISM OF ACTIVATION AND NUCLEAR BREAKDOWN IN THE CHAETOPTERUS EGG

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Abstract
1. A study has been made of activation and nuclear breakdown in Chaetopterus eggs in an effort to elucidate the various steps in the response mechanism. 2. Within two minutes after the immature egg is stimulated there is a liquefaction of the protoplasmic cortex, which occurs as a prelude to the breakdown of the nucleus. The cortical change appears to be associated with a release of calcium ions from that region. 3. Within three minutes after the initial stimulus calcium ions activate a system which acts more directly on the nucleus and which, having once been activated, no longer requires the presence of calcium ions. 4. It was postulated that the system activated by calcium involved a proteolytic enzyme. To test this possibility experiments were run utilizing crystalline trypsin. It was found that trypsin could produce nuclear breakdown in the absence of calcium and that this activity was completely blocked by soybean trypsin inhibitor. Furthermore, when eggs were placed in trypsin solutions made up in acid media (pH 3.5-4.0), nuclear breakdown still occurred, indicating that the enzyme was penetrating into the interior of the cell. 5. Preliminary experiments suggest that there is a protease in the eggs which behaves as predicted. In addition, it appears that once nuclear breakdown is effected, some mechanism comes into play to block further action of the enzyme.