Totipotent cells of parthenogenetic origin in a chimaeric mouse

Abstract

IN strain LT/Sv mice, eggs often begin to develop parthenogenetically in the ovary after the first meiotic division^1–3. They undergo apparently normal cleavage and blastocyst formation, but at the egg cylinder stage they become disorganised and form teratomas. They persist as tumours composed of many kinds of tissue, indicating that cells of parthenogenetic origin are viable. Spontaneous parthenogenesis is also common in ovulated strain LT eggs. They cleave, form blastocysts and implant in the uterus, but die shortly afterwards, in the same way that embryos derived from experimentally induced parthenogenesis die early^4–7. However, parthenogenetic cells have been ‘rescued’ by removing embryos from the oviducts of virgin females and grafting them to extrauterine sites such as testis1 and kidney⁸. Those embryos become disorganised and can survive as teratomas composed of many kinds of viable tissues. Why, then, do cells of parthenogenetic origin fail to survive in utero? To investigate this problem we are using chimaeras derived from aggregates of eight-cell parthenogenetic and normal embryos², transferred to the uteri of pseudopregnant females. We report here that early embryonic parthenogenetic cells are totipotent. They can give rise to fully functional ova which, when fertilised by sperm, develop into normal individuals.