Parthenogenesis in the Mouse

Abstract

In vitro treatment of mouse eggs with hyaluronidase can activate them to develop parthenogenetically as well as denuding them of cumulus cells^1–4. Activation and subsequent behaviour of the eggs depend on certain defined conditions. Szollosi⁵ observed morphological changes in unfertilized mouse eggs in vivo after approximately 14 h in the oviduct. Rotation and migration of the spindle towards the centre of the egg was the first and most obvious change. This prepares the egg for equal cleavage rather than the usual unequal division which results in the formation of the second polar body. Graham³ stimulated eggs 12–17 h after ovulation and obtained about 30% “immediate cleavage”⁶ in the activated group, whereas Tarkowski^7,8 applied an electric shock to the exposed oviduct 2–4 h after ovulation and obtained activation in approximately 50% but a very low incidence of immediate cleavage. This suggested that the time of activation after ovulation might be important in the type of parthenogenones induced. Eggs were considered to have undergone immediate cleavage only if, at the time of examination, they were morphologically indistinguishable from a normal fertilized two-cell egg—that is, apart from the absence of a second polar body. They resulted from a biochemical or experimental stimulus other than that provided by fertilization. The few eggs with unequal blastomeres were therefore not included in this group.