Induction of G- and R-banding in human chromosomes by the demethylating agent S-adenosyl-L-homocysteine

S-adenosyl-L-homocysteine: a non-cytotoxic hypomethylating agent

The cytotoxic effect caused by the hypomethylating agent S-adenosyl-L- homocysteine (SAH) was compared with that of two drugs commonly used to induce DNA hypomethylation, 5-azacytidine and 5-aza-2'-deoxycytidine. Two in vitro cytotoxicity tests, the tetrazolium MTT assay and the intracellular lactate dehydrogenase (LDH) activity test, suggest that SAH induces hypomethylation without causing any cytotoxic effect. We propose the use of SAH as a non-cytotoxic agent which may be more suitable for inducing experimental DNA hypomethylation.

An adaptation of the Maxam and Gilbert sequencing method to the study of human metaphase chromosomes

We have adapted the chemical DNA sequencing method developed by Maxam and Gilbert to study human metaphase chromosomes. Particularly, the in situ cytosine-specific chemical cleavage has been assayed. After exhaustive treatments, a C-like banding pattern was consistently shown. Since methyl groups interfere with the cytosine-specific chemical cleavage reaction, we assume that heterochromatin remains resistant as a result of the high level of methylation. On the other hand when moderate treatments are applied, T-bands remain as resistant regions, implying that these domains would be the most intensely methylated regions within euchromatin.