Proceeding of Veterinary and Animal Science Days 2015, 15th- 17th  July,  Milan, Italy 

riviste.unimi.it/index.php/haf                                                                                 1 

   

 

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NATHALIE BEAUJEAN  

 

Dr. Nathalie Beaujean is group 

leader at the French National 

Institute for Agricultural 

Research near Paris. Over the 

past 10 years, her team has 

developed studies on 

preimplantation development, 

genome reprogramming, and 

the control of pluripotency 

during early development, 

mainly in murine and non-

murine mammalian species. She 

is very experienced in the 

analysis of epigenetic 

reprogramming by powerful 

image analysis tools dedicated 

to the preimplantation embryos. 

One of her objectives is to better 

understand embryonic genome 

reprogramming after either 

fertilization or nuclear transfer 

(the cloning procedure). Cloning 

indeed offers a unique 

opportunity to understand how 

the oocyte's environment 

dictates the reorganization of 

the introduced nuclei, and 

thereby the transcriptional 

programs that can have 

long‐term consequences. It 

should help to establish what 

constitutes a good nuclear 

organization and to understand 

how the environment shapes the 

epigenome. 
 
 Nathalie.Beaujean@jouy.inra.frl  
 

 

Histone post-translational modifications in 

preimplantation mouse embryos and their 

role in nuclear architecture 
Nathalie BEAUJEAN 

1
 

1 
INRA, UMR1198 Biologie du Développement et Reproduction, F-78350 Jouy-

en-Josas, France 

MAIN LECTURE 

In mammals, epigenetic markers are globally rearranged after fertilization: while 
gametes carry special epigenetic signatures and a unique nuclear organization, 
they attain embryo-specific patterns after fertilization. This “reprogramming” is 
promoted by the intimate contact between the parental inherited genomes and 
the oocyte cytoplasm over the first cell cycles of development. Interestingly, 
histone post-translational modifications (PTMs) are among the factors involved in 
this reprogramming.  

During the last few years, many studies focusing on epigenetic modifications have 
indeed shown that, immediately after fertilization, different histone PTM profiles 
create an asymmetry between the two parental genomes, although both parental 
genomes undergo global hyperacetylation and hypomethylation. Thereafter, 
histone PTMs reprogramming goes on (Beaujean et al., MRD 2014). It is 
hypothesized that this PTMs reprogramming is required for the embryonic 
genome activation (EGA). Recently, we for example put forward the importance 
of the PRC1 complex that binds H3K27me3, for proper EGA and development 
beyond the two-cell stage (Posfai et al., 2012). By the stage of implantation 
(blastocyst stage) two cell subpopulations forms: an outer layer of epithelial 
trophectoderm cells (TE) and the inner cell mass (ICM) located eccentrically within 
the blastocoelic cavity. Remarkably, some histone PTMs have been found to differ 
between the ICM vs. TE and to correlate with specific gene expression in each of 
these cell types (Dahl et al., 2010; Vermilyea et al., 2009).  

On the other hand, it is well known that diverse parts of the genome have 
different types of chromatin configuration depending on their function 
(centromeric and telomeric heterochromatin for instance). Interestingly, the 
mouse embryo presents a unique organization of the peri-centromeric 
heterochromatin that locates around the nucleoli. This configuration is rapidly 
acquired in the maternal pronucleus and more progressively in the paternal one 
(Martin et al., 2006; Aguirre-Lavin et al., 2012), probably due to the specific 
epigenetic marks present only in the paternal chromatin. During the 2-cell stage, 
dissociation of pericentromeric heterochromatin from nucleoli begins, 
concomitantly with the major phase of embryonic genome activation, although 
the importance of this remodeling is not yet well understood. Remarkably, it 
however seems that transcripts generated by pericentromeric satellite repeats 
are involved in this event and that interference with this phenomenon results in 
developmental arrest (Probst et al., 2010; Santenard et al., 2010; Fulka & 
Langerova 2014).  
Altogether, it suggests that histone PTMs may be closely correlated with the 
formation of a transcriptionally active or repressive state during early embryonic 
development and that they can modify chromatin organization and nuclear 
architecture during mouse embryonic development. It should also be mentioned 
that knock-outs of several histone modification enzymes have underlined the 
importance of PTMs during preimplantation development. 

 

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