The expression of a transgene NI-ROSA LacZ (LacZtg) trapped into the genes for two presumably untranslated, ubiquitously expressed RNAs, was studied in preimplantation mouse embryos with respect to penetrance (fraction of expressing embryos) and to localisation of β-galactosidase activity. With maternal origin in NMRI mice β-galactosidase was first detected within one dot in the cytoplasm of zygotes at 30 h post-hCG. The staining pattern progressed to small clusters and to dense, homogeneous staining of the entire cytoplasm during further development. Within the NMRI background, penetrance in utero was delayed by at least 6 h when the transgene was of paternal as compared with maternal origin. Paternal transgene expression increased marginally during culture to 50 h after explantation of embryos at 30-48 h post-hCG and remained low or decreased in the ‘2-cell block’. Expression of a paternal transgene in preimplantation embryos developing in utero was further delayed in the maternal MF1 as compared with the NMRI background. In contrast to NMRI × NMRI embryos with paternally derived transgene, expression increased with time during the 2-cell block in MF1 × NMRI embryos. Thus, in the earliest phase of mammalian development expression of this LacZtg is influenced by parental origin, maternal genetic background and environment. The spatial distribution of the gene product is developmentally controlled.
Treatment of Haemolytic Disease of the Newborn Due to Rh-immunization