Allele-specific methylation in the non-inprinted gene

K18 gene is methylated in an allele-specific manner in U937 myelomonocytic cells. Unimprinted genes may also have allele-specific methylation. This allele-specificity may not depend on parental sex.

Discussion
1. Allele specific methylation is maintained during hundreds of cell division or passage. This allele-specific methylation is probably maintained from the generation of the cell line. This indicates that maintenance of methylation is extremely precise.

2. De novo methylase activity is not present at all in the U-937 cells.
De novo methyltransferase activity is obviously present in ES cells. When the hK18 gene is transfected into ES cells, the enhancer of the gene gets methylated. Interestingly, ratio of methylation to non-methylation of the ETS site in exogenously transfected K18 gene is almost the same as that in the endogenous K18 gene.

3. Maintenance methylase activity is present or maybe strong in the cells.

4. Difference in methylation is thought to happen after each division. If these methylation status occurs during long range of cell cultures, pattern of methylation should be the same. However, methylation pattern is random in each cell. Furthermore, maintenance methylase made some mistakes in cells, or the amount of methylation gradually decreases.

5. I do not know what made allele-specific methylation, though.

SCD gene may also have another allele-specific methylation. Again, the SCD gene is not an imprinting gene.