Hypomethylation of alphoid DNA and classical satellite DNA on chromosome 1, 9, 16 and Y in extraembryonic tissue.

The pattern of DNA methylation can be analyzed on methaphase chromosomes with fluorescein labeled antibodies against 5-methylcytosine. In human extraembryonic tissue lower overall intensity of immunofluorescence in centromeric chromosomal regions correspond to hypomethylation of the DNA when compared with normal human lymphocytes. Pericentromeric regions on chromosomes 1,9,16 and heterochromatin on chromosome Y, which reveal lower levels of immunofluorescence, are rich in classical satellite DNA type II and III. In our experiment methylation-sensitive restriction enzymes, alphoid and classical satellite DNA probes specific for chromosomes 1,9,16 and Y were used. Southern blot analysis on cells from extraembryonic tissue revealed different extent of hypomethylation in different chromosomal regions. Our results confirm overall and sequence-specific hypomethylation of DNA in cells from extraembryonic tissue in comparison with somatic cells.