Nucleolar transplantation in oocytes and zygotes: challenges for further research

In germinal vesicles of immature mammalian oocytes, including humans, as well as in pronuclei in 1-cell stage embryos, prominent nuclear organelles, nucleoli, can be easily detected even under a relatively low magnification. In humans, it has been clearly documented that their number, position and distribution in pronuclei can be used as an indicator of embryonic developmental potential. In the light of some recent experiments showing the feasibility of nucleolar manipulation we discuss here if these new approaches can be used to rescue those embryos with abnormal pronuclear nucleolar patterns.