PECULIARITIES OF METAPHASE CHROMOSOME METHYLATION PATTERN IN PREIMPLANTATION HUMAN
EMBRYOS
V. S. Baranov,1 A. A. Pendina,1 T. V. Kuznetzova,1
O. A. Efimova,2 I. D. Fedorova,1
O. A. Leontieva,3 V. S. Korsak,3 N. N. Nikolsky 4
1 D. O. Ott's Institute of Obstetrics and Gynccology, RAMS, St. Petersburg;
2 Department of Genetics and Breeding, St. Petersburg State University, 3 International Center of
Reproductive Medicine, and 4 Institute of Cytology, RAS, St. Petersburg, Russia;
e-mail: pendina@mail.ru
Methylation pattern peculiarities revealed by immunocytochemical analysis of metaphase chromosomes from
preimplanted human embryos with monoclonal antibodies against 5-methylcytosine are described. Chromosomes of 2-8-cell triploid
human embryos are undermethylated, if compared to those from PHA-stimulated fetal cord blood lymphocytes. Hemimethylation
(asymmetric labeling of sister chromatids) is typical for the most of embryonic chromosomes at 2-cell-blastocyst stages due
most probably to a passive loss of methylation during initial cleavages. Diffuse labeling and sister chromatid exchanges are two
other cytogenetic peculiarities revealed by immunofluorescent staining of early human embryos. Hypomethylation of pericentromeric
heterochromatin of chromosomes 1, 9, 16 and different methylation status of some homologous chromosomes may distinguish them
from metaphase chromosomes of lymphocytes. M-banding pattern typical for chromosomes from adult and cord blood lymphocytes
initially appears in embryonic metaphase chromosomes as early as at a 8-cell stage to be established for most part of chromosomes
of the karyotype at the morula-blastocyst stage only.
Key words: DNA methylation of metaphase chromosomes, human embryogenesis, preimplantation human embryos,
heterochromatin, triploidy
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