In vitro activation of mouse eggs.

Unfertilized mouse eggs were activated in vitro with hyaluronidase. Subsequently they were exposed to culture medium at different osmolarities. In full strength White's culture medium they tended to form one pronucleus and a second polar body. The majority of these eggs were haploid. In 4/5 and 3/5 dilutions of this medium, the second polar body formation was suppressed and eggs tended to form with one or two pronuclei. Those with one pronucleus were diploid and those with two pronuclei could either form a diploid or form a haploid mosaic. Old eggs tended to immediately cleave and form haploid mosaics. DNA synthesis was studied in activated eggs using tritiated thymidine and autoradiography. DNA synthesis occurred at a similar time in fertilized and activated eggs.