J. Ma et al., Regulation of zygotic gene activation in the preimplantation mouse embryo:Global activation and repression of gene expression, BIOL REPROD, 64(6), 2001, pp. 1713-1721
Superimposed on the activation of the embryonic genome in the preimplantati
on mouse embryo is the formation of a transcriptionally repressive state du
ring the two-cell stage. This repression appears mediated at the level of c
hromatin structure, because it is reversed by inducing histone hyperacetyla
tion or inhibiting the second round of DNA replication. We report that of m
ore than 200 amplicons analyzed by mRNA differential display, about 45% of
them are repressed between the two-cell and four-cell stages. This repressi
on is scored as either a decrease in amplicon expression that occurs betwee
n the two-cell and four-cell stages or on the ability of either trichostati
n A tan inhibitor of histone deacetylases) or aphidicolin tan inhibitor of
replicative DNA polymerases) to increase the level of amplicon expression.
Results of this study also indicate that about 16% of the amplicons analyze
d likely are novel genes whose sequence doesn't correspond to sequences in
the current databases, whereas about 20% of the sequences expressed during
this transition likely are repetitive sequences. Lastly, inducing histone h
yperacetylation in the two-cell embryos inhibits cleavage to the four-cell
stage. These results suggest that genome activation is global and relativel
y promiscuous and that a function of the transcriptionally repressive state
is to dictate the appropriate profile of gene expression that is compatibl
e with further development.