Pluripotent stem cells from maturing oocytes.

Embryonic stem cells are mostly derived from mature oocytes that were either fertilized or activated parthenogenetically and then reached the blastocyst stage. From the cell cycle perspective, fertilization or activation induces the exit from meiosis, decondensation of oocyte chromosomes, and the entry into mitosis. Decondensation of oocyte chromatin with subsequent formation of nuclei can be, however, induced at any postgerminal vesicle breakdown meiotic maturation stage. In this article, we discuss the possibility of cleavage of transformed maturing oocytes and whether they can reach the blastocyst stage, from which pluripotent stem cell lines could be derived.