Til 1--a human lymphoblastoid cell line with minimal DNA methylation.

Methylation has been shown to be correlated with several fundamental cellular processes, including changes in gene expression, alterations in chromatin structure and inactivation of the mammalian X chromosome. It is possible, therefore, that the methylation status of a particular sequence may reflect involvement in a number of processes. Given this potentially confused situation, it is clear that many studies would be facilitated if unmethylated or minimally methylated DNA from a mammalian source were available. A major use of such DNA would be in the construction of long-range physical maps. In many cases, long-range physical maps are a prerequisite for the eventual isolation of disease genes that have been localised to a particular chromosomal region by other means (e.g. genetic linkage studies). Many of the enzymes used in such long-range mapping experiments are methylation sensitive, which makes it difficult to determine how many sites for a particular enzyme are present in any DNA sequence. Here we report the finding of a minimally methylated DNA in the human lymphoblastoid cell line, Til 1. The methylation level of Til 1 DNA was analysed in several ways and compared with that in human lymphocytes, placental tissue and other lymphoblastoid cell lines. The results showed clear and reproducible differences in methylation among the cell types, both at a global level and in the vicinities of specific DNA sequences. Lymphocyte DNA had the highest level of methylation while placental DNA and cell line DNA had lower but similar levels. Til 1 had abnormally low levels of 5-methylcytosine when measured directly, and no detectable methylation at any of the restriction sites examined.