Retarded postimplantation development of XO mouse embryos: Impact of the parental origin of the monosomic X chromosome

About 12-17% of the embryos obtained by mating mice carrying the In(X)1H or Paf mutations are of the 39,X (X0) genotype. Depending on the mutant mice used for mating, the monosomic X chromosome can be inherited from the paternal (X-P) Or the maternal (X-M) parent. The X(P)0 embryos display developmental retardation at gastrulation and early organogenesis. X(P)0 embryos also display poor development of the ectoplacental cone, which is significantly smaller in size and contains fewer trophoblasts than XX siblings. In contrast, X(M)0 embryos develop normally and are indistinguishable from XX littermates. In both types of X0 embryos, an X-linked lacZ transgene is expressed in nearly all cells in both the embryonic and the extraembryonic tissues, suggesting that X inactivation does not occur when only one X is present. Of particular significance is the maintenance of an active X-P chromosome in the extraembryonic tissues where normally the paternal X chromosome is preferentially inactivated in XX embryos. The differential impact of the inheritance of X chromosomes from different parents on the development of the X0 embryos raises the possibility that the X-P is less capable than the X-M in providing the appropriate dosage of X-linked activity that is necessary to support normal development of the embryo and the ectoplacental cone. Alternatively, the development of the X(P)0 embryo may be compromised by the lack of activity of one or several X-linked genes which are expressed only from the maternal X chromosome. Without the activity of these genes, embryonic development may be curtailed even though all other loci on the X-P chromosome are actively transcribed. (C) 1998 Academic Press.