Maternal T^hp lethality in the mouse is a nuclear, not cytoplasmic, defect

Abstract

The T^hp mutation, an allele of the mouse T/t complex, differs from other known mutations in that its effects are determined by the sex of the parent from which it is inherited; when inherited from the female parent, it is invariably lethal at the embryonic stage, but, most embryos which inherit the mutation from the male parent survive^1,2. Thus most heterozygous embryos carrying the maternally derived mutation die in the second half of pregnancy, while the exceptional embryos surviving to parturition give oedematous, cyanotic individuals that die within 24 h^3,4. The lethal maternal effect of T^hp may be transmitted either through the cytoplasm of the ovum (oogenic defect) or through the female pronucleus (embryogenic defect). Here we have sought to decide between these possibilities by performing reciprocal nuclear transplantations⁵ between one-cell embryos from T^hp/+ and +/+ females. Our observation that this maternally inherited lethal effect of T^hp persists when T^hp/+ pronuclei are transplanted into +/+ cytoplasm suggests that the defect responsible for the pattern of inheritance lies in the pronuclei and not the cytoplasm.