title: Parthenogenetic activation of mouse oocytes by exposure to strontium as a source of cytoplasts for nuclear transfer.
abstract: Cell-cycle phase of the donor and recipient cells at the moment of nuclear transfer influences subsequent development of the reconstituted embryo. In order to study this effect, the precise cell-cycle phase of the recipient oocyte at the time of fusion must be known and this depends on reliable activation of oocytes in a protocol that has a low incidence of spontaneous activation. Mouse oocytes recovered before (8-10 hours post-human chorionic gonadotropin [hCG]) and after ovulation (14 and 18 hours post-hCG) were exposed to strontium ions in calcium magnesium-free M16 culture medium. The effect on development of haploid parthenotes of post-hCG age of the oocyte, the duration of exposure, and strontium concentration in the medium was determined. These experiments established a reliable method of parthogenetic activation of recently ovulated mouse oocytes, involving the culture of oocytes for 60 minutes in 25 mM strontium in a calcium magnesium-free M16 medium. This method of activation was also able to induce activation of preovulatory oocytes after a preincubation period in vitro. Only a low incidence of spontaneous activation was observed if oocytes were recovered before or immediately after ovulation (14 hours after hCG).
authors.affiliation: Roslin Institute (Edinburgh), Roslin, Midlothian, United Kingdom.
authors.forename: P J
authors.initials: PJ
authors.lastname: Otaegui
authors.forename: G T
authors.initials: GT
authors.lastname: O'neill
authors.forename: I
authors.initials: I
authors.lastname: Wilmut