Restriction landmark genomic scanning for DNA methylation in cancer: past, present, and future applications

The field of molecular biology was revolutionized by the advent of gel electrophoresis. Restriction landmark genomic scanning (RLGS) is a type of two-dimensional electrophoresis employed in the genome-wide assessment of genomic alterations. RLGS has been used to study genetic and epigenetic changes in normal tissues, primary tumors, cancer cell lines, and various organisms such as mice, rats, hamsters, bacteria, and plants. An RLGS profile displays over 2000 radiolabeled restriction landmark sites in a single assay. When conducted with methylation-sensitive restriction enzymes whose sites are preferentially located in CpG island regulatory regions, RLGS becomes a very versatile tool for the investigation of both normal and aberrant methylation patterns. Early studies performed on tumor DNA were mainly descriptive in nature, essentially a catalogue of loci that were changed to varying degrees in different tumor types. Over time, as investigators have become more proficient with RLGS and have undertaken high-throughput studies, the need for efficient cloning, imaging, and analysis systems has become paramount. Current studies focus on identifying specific genes and pathways involved in deregulated methylation in cancer. As such, RLGS analysis of tumor samples has made tremendous contributions to our understanding of the role of DNA methylation in cancer. Future directions will take advantage of the abundant genomic sequence data available to link all of the RLGS loci to genes and create biologically relevant methylation profiles of cancer. This review discusses practical considerations of using RLGS as a genome scanning tool and the past, present, and future applications in cancer biology.