DIFFERENTIAL H4 ACETYLATION OF PATERNAL AND MATERNAL CHROMATIN PRECEDES DNA-REPLICATION AND DIFFERENTIAL TRANSCRIPTIONAL ACTIVITY IN PRONUCLEI OF 1-CELL MOUSE EMBRYOS
Pg. Adenot et al., DIFFERENTIAL H4 ACETYLATION OF PATERNAL AND MATERNAL CHROMATIN PRECEDES DNA-REPLICATION AND DIFFERENTIAL TRANSCRIPTIONAL ACTIVITY IN PRONUCLEI OF 1-CELL MOUSE EMBRYOS, Development, 124(22), 1997, pp. 4615-4625
In the mouse embryo, transcriptional activation begins during S/G(2) p
hase of the first cell cycle when paternal and maternal chromatin are
still in separate nuclear entities within the same cytoplasm, At this
time, the male pronucleus exhibits greater transcriptional activity th
an the female pronucleus, Since acetylation of histones in the nucleos
ome octamer exerts a regulatory influence on gene expression, we inves
tigated changes in histone acetylation during the remodeling of patern
al and maternal chromatin from sperm entry through to minor genome act
ivation and mitosis, We found (1) neither mature sperm nor metaphase I
I maternal chromatin stained for hyperacetylated histone H4; (2) immed
iately following fertilization, hyperacetylated H4 was associated with
paternal but not maternal chromatin while, in parthenogenetically act
ivated oocytes, maternal chromatin became hyperacetylated; (3) in zygo
tes, differential levels and patterns of hyperacetylated H4 between ma
le and female pronuclei persisted throughout most of G(1) with histone
deacetylases and acetyltransferases already active at this time; (4)
when transcriptional differences are observed in S/G(2), male and fema
le pronuclei have equivalent levels of H4 hyperacetylation and DNA rep
lication was not required to attain this equivalence and (5) in contra
st to the lack of H4 hyperacetylation on gametic chromatin, chromosome
s at the first mitosis showed distinct banding patterns of H4 hyperace
tylation, These results suggest that sperm chromatin initially out-com
petes maternal chromatin for the pool of hyperacetylated H4 in the ooc
yte, that hyperacetylated H4 participates in the process of histone-pr
otamine exchange in the zygote, and that differences in H4 acetylation
in male and female pronuclei during G(1) are translated across DNA re
plication to transcriptional differences in S/G(2). Prior to fertiliza
tion, neither paternal nor maternal chromatin show memory of H4 hypera
cetylation patterns but, by the end of the first cell cycle, before ma
jor zygotic genome activation at the 2-cell stage, chromosomes already
show hyperacetylated H4 banding patterns.