Activation of cumulus-free mouse oocytes.

Attempts were made to activate parthenogenetically oocytes from random-bred mice under conditions required for nuclear transfer, viz. in the absence of cumulus cells. Of the large number of stimulants previously described and presumed to be generally effective, only exposure to strontium ion (as a replacement for calcium ion in the medium), or to calcium ionophore, activated a substantial proportion of cumulus-free oocytes from TRf mice, a synthetic, random-bred strain. These stimuli were less effective in oocytes from random-bred ICR mice. The relevance of the findings to nuclear-transfer cloning attempts in mice is discussed.