Pendina A A, Efimova O A, Fedorova I D, Leont'eva O A, Shilnikova E M, Lezhnina J G, Kuznetzova T V, Baranov V S
D.O. Ott's Research Institute of Obstetrics and Gynecology of the Russian Academy of Medical Science, Laboratory for Prenatal Diagnosis of Human Inborn and Inherited Diseases, Mendeleevskaya Line 3, Saint-Petersburg, Russia.
Cytogenet Genome Res. 2011;132(1-2):1-7. doi: 10.1159/000318673. Epub 2010 Aug 17.
We performed a stage-by-stage study of DNA methylation patterns in metaphase chromosomes from blastomeres of triploid and abnormal diploid human embryos. QFH-banded homologous parental chromosomes differ in their DNA methylation patterns at the metaphase of the 1st cleavage division. Chromosomes of both parental genomes are gradually demethylated at subsequent cleavages, undergoing hemimethylation in 2-cell embryos. At the 4-cell stage hypomethylated chromosomes initially appear and are further registered until the blastocyst stage. The proportion of hemimethylated and hypomethylated chromosomes varies between the blastomeres since the 4-cell stage with no preference for certain chromosomes to be hemi- or hypomethylated demonstrates random segregation of hypomethylated, undermethylated and methylated chromatids during cell cleavage. By the blastocyst stage the chromosomes acquire band- and, thus, chromosome-specific methylation patterns, with 5-methylcytosine-rich DNA preferentially accumulated in R- and T-bands and in the short arms of acrocentric chromosomes. Thus, demethylaton and remethylation of parental genomes of human embryos proceeds in the same manner from the 1st metaphase stage up to the blastocyst. These processes involve all chromosomes and all bands from each chromosome and lead to establishment of chromosome-specific DNA methylation patterns by the blastocyst stage with no differences between homologous chromosomes.
我们对三倍体和异常二倍体人类胚胎卵裂球中期染色体的DNA甲基化模式进行了分阶段研究。QFH带型的同源亲本染色体在第一次卵裂中期的DNA甲基化模式存在差异。两个亲本基因组的染色体在随后的卵裂过程中逐渐去甲基化，在二细胞胚胎中经历半甲基化。在四细胞阶段，低甲基化染色体最初出现并一直持续到囊胚阶段。自四细胞阶段起，卵裂球中半甲基化和低甲基化染色体的比例各不相同，没有特定染色体倾向于半甲基化或低甲基化，这表明在细胞分裂过程中低甲基化、甲基化不足和甲基化染色单体随机分离。到囊胚阶段，染色体获得带型，进而形成染色体特异性甲基化模式，富含5-甲基胞嘧啶的DNA优先积累在R带和T带以及近端着丝粒染色体的短臂中。因此，人类胚胎亲本基因组的去甲基化和重新甲基化从第一次中期阶段到囊胚阶段以相同方式进行。这些过程涉及所有染色体以及每条染色体的所有带型，并导致在囊胚阶段建立染色体特异性DNA甲基化模式，同源染色体之间没有差异。
