The chromosome make-up of laboratory produced sheep embryos

We characterized the chromosome complement of domestic sheep embryos produced by in vitro fertilization, somatic cell nuclear transfer, parthenogenesis and artificial insemination to determine if the incidence of chromosome abnormalities is higher in laboratory-produced embryos. FISH analysis with commercially available painting probes and conventional chromosome analysis were performed on sheep embryos produced by: (i) surgical flushing of the uterine horns of superovulated sheep six days after insemination, (ii) in-vitro fertilization of in-vitro-matured oocytes, followed by in-vitro culture for six days, (iii) parthenogenic activation of in-vitro-matured oocytes with an electrical pulse and exposure to 6DMAP or cycloheximide followed by in-vitro culture for six days, (iv) reconstruction of invitro- matured oocytes and fetal fibroblasts (cloning) activated by an electrical pulse and exposure to 6DMAP or cycloheximide followed by in-vitro culture for six days. All types of in-vitro-produced embryos contained significantly higher frequencies of embryos containing chromosomally abnormal cells than in-vivo-produced controls. Among all types of embryos, including those produced in-vivo, themost common abnormal chromosomal complement was tetraploidy. These observations suggest that irregularities in cell division leading to polyploidy are a common feature of embryo development, which is exacerbated by in-vitro production. The relationship and potential causality between higher incidences of chromosomally abnormal cells and other abnormalities reported in laboratory-produced embryos remain to be elucidated. (Funded by CRC, OMAF.)