Dynamics of constitutive heterochromatin: two contrasted kinetics of genome restructuring in early cloned bovine embryos.
Efficient reprograming of the donor cell genome in nuclear transfer (NT) embryos is linked to the ability of the embryos to sustain full-term development. As the nuclear architecture has recently emerged as a key factor in the regulation of gene expression, we questioned whether early bovine embryos obtained from transfer of cultured fibroblasts into enucleated oocytes would adopt an embryo-like nuclear organization. We studied the dynamics of constitutive heterochromatin in the stages prior to embryonic genome activation by distribution analysis of heterochromatin protein CBX1 (HP1), centromeric proteins CENPA and CENPB, and histone H3 three-methylated at lysine 9. Then we applied descriptive, quantitative, and co-localization analyses. A dramatic reorganization of heterochromatic blocks of somatic donor cells was first observed in the late one-cell stage NT embryos. Then at two- and four-cell stages, we found two types of NT embryos: one displaying noncondensed heterochromatin patches similar to IVF embryos, whereas the second type displayed condensed heterochromatin blocks, normally observed in IVF embryos only after the eight-cell stage. These analyses discriminate for the first time two contrasted types of nuclear organization in NT embryos, which may correspond to different functional states of the nuclei. The relationship with the somatic nucleus reprograming efficiency is discussed.
Pichugin
Andrey
A
INRA, UMR 1198 Biologie du développement et reproduction, F-78350 Jouy en Josas, France.
Le Bourhis
Daniel
D
Adenot
Pierre
P
Lehmann
Gaëtan
G
Audouard
Christophe
C
Renard
Jean-Paul
JP
Vignon
Xavier
X
Beaujean
Nathalie
N
D000818:Animals; D001324:Autoantigens / Q000378:metabolism; D002417:Cattle; D002467:Cell Nucleus / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D065150:Cellular Reprogramming; D000076247:Centromere Protein A; D051936:Centromere Protein B / Q000378:metabolism; D042002:Chromatin Assembly and Disassembly; D000090266:Chromobox Protein Homolog 5; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D019976:Cloning, Organism / Q000379:methods; D003594:Cytoplasmic Granules / Q000378:metabolism / Q000648:ultrastructure; D004622:Embryo, Mammalian / Q000378:metabolism* / Q000648:ultrastructure; D047108:Embryonic Development; D005307:Fertilization in Vitro; D005347:Fibroblasts; D006570:Heterochromatin / Q000145:classification / Q000378:metabolism* / Q000648:ultrastructure; D006657:Histones / Q000378:metabolism; D007700:Kinetics; D018613:Microscopy, Confocal; D053652:Nuclear Transfer Techniques; D009865:Oocytes
D001324:Autoantigens; D000076247:Centromere Protein A; D051936:Centromere Protein B; D002868:Chromosomal Proteins, Non-Histone; D006570:Heterochromatin; D006657:Histones; D000090266:Chromobox Protein Homolog 5