Gene expression of the mouse reproduced without meiotic division

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We cloned mice from the nuclei of fresh or primary cultured donor cells with defined genetic backgrounds under standardized experimental conditions. Most (99/107)clones developing to term were alive and apparently normal. Imprinted genes were all expressed "from appropriate parental alleles in both the cloned embryos and their placentas. However, " significantly reduced transcript levels for several imprinted and non-imprinted genes occurred in clone-associated placentas (which were invariably hypertrophic) although to a "minimal extent in corresponding fetuses. Transcript levels for Igf2 and H19, imprinted" "genes presumed to be prone to cloning-induced epimulation, were within the control range." "Thus, cloning by nuclear transfer does not quantitatively perturb parent-specific imprinting" "memory established during gametogenesis. Moreover, the epigenetic effects of nuclear" "transfer cloning are not stochastic, and can be traced to specific genes expressed in the" placenta. Genomic … More imprinting is an epigenetic mechanism that causes functional differences between "paternal and maternal genomes, and plays an essential role in mammalian development." Stage-specific changes in the DNA methylation patterns of imprinted genes suggest that "their imprints are erased some time during the primordial germ cell (PGC) stage, before" their gametic patterns are re-established during gametogenesis according to the sex of individuals. To define the exact timing and pattern of the erasure "process, we analyzed parental-origin-specific expression of imprinted genes and DNA" "methylation patterns of differentially methylated regions (DMRs) in embryos, each derived" from a single day -11.5 to day -13.5 PGC by nuclear transfer. Analysis of DNA methylation in day -10.5 to -12.5 PGCs demonstrated that PGC clones represented the DNA methylation status of donor PGCs well. These findings provide strong evidence that the erasure process "of genomic imprinting memory proceeds in the day -10.5 to -11.5 PGCs, with the timing" precisely controlled for each imprinted gene. Less