5-Methylcytosine and 5-hydroxymethylcytosine spatiotemporal profiles in the mouse zygote.
BACKGROUND
In the mouse zygote, DNA methylation patterns are heavily modified, and differ between the maternal and paternal pronucleus. Demethylation of the paternal genome has been described as an active and replication-independent process, although the mechanisms responsible for it remain elusive. Recently, 5-hydroxymethylcytosine has been suggested as an intermediate in this demethylation.


RESULTS
In this study, we quantified DNA methylation and hydroxymethylation in both pronuclei of the mouse zygote during the replication period and we examined their patterns on the pericentric heterochromatin using 3D immuno-FISH. Our results demonstrate that 5-methylcytosine and 5-hydroxymethylcytosine localizations on the pericentric sequences are not complementary; indeed we observe no enrichment of either marks on some regions and an enrichment of both on others. In addition, we show that DNA demethylation continues during DNA replication, and is inhibited by aphidicolin. Finally, we observe notable differences in the kinetics of demethylation and hydroxymethylation; in particular, a peak of 5-hydroxymethylcytosine, unrelated to any change in 5-methylcytosine level, is observed after completion of replication.


CONCLUSIONS
Together our results support the already proposed hypothesis that 5-hydroxymethylcytosine is not a simple intermediate in an active demethylation process and could play a role of its own during early development.
INRA, UMR1198 Biologie du Développement et Reproduction, Jouy-en-Josas, France. juliette.salvaing@jouy.inra.fr
Juliette
J
Salvaing
Tiphaine
T
Aguirre-Lavin
Claire
C
Boulesteix
Gaëtan
G
Lehmann
Pascale
P
Debey
Nathalie
N
Beaujean
D044503:5-Methylcytosine / Q000378:metabolism* / Q000031:analogs & derivatives; D000818:Animals; D002453:Cell Cycle; D003596:Cytosine / Q000031:analogs & derivatives* / Q000378:metabolism; D019175:DNA Methylation; D004261:DNA Replication; D005260:Female; D006570:Heterochromatin / Q000378:metabolism; D008297:Male; D051379:Mice; D013997:Time Factors; D015053:Zygote / Q000166:cytology / Q000378:metabolism*
D006570:Heterochromatin; C011865:5-hydroxymethylcytosine; D044503:5-Methylcytosine; D003596:Cytosine