Until now, scientists investigating human cloning for therapeutic purposes have been limited to using mature eggs (oocytes) that have reached the metaphase II stage (MII) at which ovulation and fertilisation occurs in humans. However, there are few human MII oocytes available for research because almost all that are retrieved from women seeking fertility treatment are used to treat the patient. Immature oocytes are not used routinely for treatment at present, and so any that are retrieved can be donated for research. These immature oocytes are arrested in the prophase I stage, before meiotic division is complete, when the enlarged nucleus is called the germinal vesicle (GV).
Bjorn Heindryckx, a PhD student at the Infertility Centre at Ghent University Hospital, Belgium, and his colleagues, matured GV oocytes in culture in the laboratory for 44 hours, after which time 85% of the GV oocytes had developed into MII oocytes. From each of these, they removed the nuclear apparatus, which contained the chromosomes that held all the genetic information. Using conventional ICSI techniques, they injected into the empty oocytes the nuclei taken from somatic cumulus1 cells (i.e. non-germ cells) of another person ?a process known as non-autologous nuclear transfer. After time for nuclear re-programming the oocytes were artificially activated by incubation in a medium containing calcium ionophore, which enabled the injected nucleus to prepare for the first embryonic division.
Mr Heindryckx said: "Eighteen out of the 25 in vitro matured MII oocytes survived
Source:European Society for Human Reproduction and Embryology