Printed in Great Britain © Company of Biologists Limited igyS INDUCTION OF CLEAVAGE IN NUCLEATED AND ENUCLEATED FROG EGGS BY INJECTION OF ISOLATED SEA-URCHIN MITOTIC APPARATUS

Mitotic apparatus (MA) were isolated in glycerol-dimethylsulphoxide solution (MTME) from zygotes of sea urchins {Strongylocentrotus purpuratus). Freshly isolated MA were stored in. 1/10 strength MTME for varying periods of time and were then injected into unfertilized frog (Rana pipiens) eggs. These injections induced 40-60 % of the recipient frog eggs to initiate cleavage, resulting in the formation of blastula cell clusters. The cleavage-inducing activity of MA stored in 1/10 MTME at room temperature decreased with time of storage in 1/10 strength MTME, and disappeared by about 6 h. There was no change in the ultra-structure of MA during storage. MA isolated and stored in MTME at room temperature had a constant level of cleavage-inducing activity during the first 48 h of storage, but this activity slowly declined upon further storage; almost no activity was left after 3 weeks. MA isolated in hexylene glycol (HG) and immediately transferred into MTME were compared with MA isolated in MTME; both MA had the same cleavage-inducing activity on the day of isolation, after which the MA isolated in HG quickly lost activity. On the other hand, MA isolated and stored in HG had little cleavage-inducing activity when tested 3