PARENTAL IMPRINTING ON THE MOUSE-X CHROMOSOME - EFFECTS ON THE EARLY DEVELOPMENT OF XO, XXY AND XXX EMBRYOS

To examine the effects of X-chromosome imprinting during early mouse embryogenesis, we attempted to produce X(M)0, X(P)0, X(M)X(M)Y, X(M)X(P)Y and X(M)X(M)X(P) (where X(M) and X(P) stand for the maternally and the paternally derived X chromosome, respectively) making use of mouse strains bearing the translocation Rb(X.2)2Ad and the inversion In(X)1H. Unlike X(M)X(P)Y embryos, X(M)X(M)Y and X(M)X(M)X(P) conceptuses suffered from severe growth retardation or abnormal development characterized by deficient extra-embryonic structures at 6.5-7.5 days post coitum (dpc). A cytogenetic study suggested that two X(M) chromosomes remaining active in certain nonepiblast cells were responsible for the serious developmental abnormality found in these embryos disomic for X(M). Although matings involving females heterozygous for Rb(X.2)2Ad hinted at the paucity of X(P)0 embryos relative to those having the complementary karyotype of X(M)X(M)X(P), further study of embryos from matings between females heterozygous for In(X)1H and Rb2Ad males did not substantiate this observation. Thus, the extensive peri-implantation loss of X(P)0 embryos shown by Hunt (1991) may be confined to XO mothers. Taken together, this study failed to reveal a parentally imprinted X-linked gene essential for early mouse embryogenesis other than the one most probably corresponding to the X-chromosome inactivation centre.