Investigation on the low temperature resistance of mouse pronuclei by using nuclear transplantation technique

Abstract

The study was undertaken to examine whether the resistance of pronuclei and cytoplasm to the low temperature was different in the mouse fertilized eggs. At the first experiment, fertilized eggs at pronucleus stage were preserved at 3.6°C for 24, 48, 72 and 96 h, and then cultured in vitro for 1 to 4 days. At the second experiment, pronuclei were removed from the eggs previously preserved for 96 to 216 hrs at 3.6°C, and then were transplanted into enucleated cytoplasm of fresh fertilized eggs. The results obtained are as follows. 1) The proportion of eggs developed to 2-cell stage was significantly low when eggs were preserved for 24 h at 3.6°C (64%) compared with that obtained in fresh eggs (97%). The eggs preserved for more than 72 hrs did not develop to 2-cell stage. 2) On the contrary, as for the rate of pronuclei exchanged eggs developed to 2-cell stage there was no significant difference between pronuclei preserved for 96 (90.0%) and 216 hrs (64%) at 3.6°C. Moreover, 1 live young was obtained after the transfer of pronuclei exchanged eggs which were preserved for 96 h at the low temperature. 3) The present study clearly demonstrated that the pronuclei were more resistant to the low temperature than the cytoplasm in the mouse eggs.