Derivation of mammalian haploid embryonic stem cells and their development potentials. (A) Reconstruction of mouse androgenetic haploid embryos by the sperm nuclear transfer (NT) process. Mouse androgenetic haploid embryonic stem (ahES) cells could be derived from these embryos via embryonic stem cell derivation and fluorescence-activated cell sorting (FACS) enrichment. Fertile mice could then be obtained by the intracytoplasmic ahES cell injection (ICAI) procedure. (B) Derivation of mouse parthenogenetic haploid embryonic stem (phES) cells and production of fertile mice by substituting maternal genomes of zygotes with phES cells. (C) Derivation of monkey phES cells. Whether the monkey phES could support embryonic development via the intracytoplasmic phES cell injection (ICPI) process is not yet clear. CHX, cycloheximide; MII, metaphase II.