DYNAMIC MOLECULAR COMBING OR DMC

The new methods of whole genome sequencing provide refined tools for physical mapping of genome. Traditional approaches include sequenced tagged sites (STS), content ordering of large insert clones (YAC) or bacterial artificial chromosomes (BAC) and restriction mapping of sets of smaller clones. All these procedures provide physical maps of the genome but are difficult to perform and are time consuming. In addition, technologies based on PCR or cytogenetic studies do not have adequate resolution which is required for screening for genetic diseases and in molecular diagnostics. Michalet et al, in the September 5^th, 1997 issue of Science describe a new technology for high resolution physical mapping of the genome. The technique which is called "Dynamic Molecular Combing or DMC" allows precise measurement at the range of 7-150 kilobases which clearly far exceeds that achieved by the conventional techniques. The simplicity, reproducibility and precision of this technique make it an ideal technique for genomic studies. The technique includes the following steps:

1. Silanize coverslips.
2. Dip the silanized coverslips into a buffered solution containing genomic DNA.
3. Incubate the coverslips in the solution for 5 min. During incubation, the DNA molecules bind to the surface of converslips.
4. Pull out the coverslips from the solution using an apparatus that allows the coverslips to be removed vertically at 300 mm/s. The distal part of each DNA molecule binds to the coverslip in the solution. While the coverslip is being removed vertically, the DNA molecules stretch and continue to bind to the emerged surface of the coverslip.
5. The emerged hydrophobic surface of the silanized coverslip rapidly dries out allowing the DNA molecules to fix as parallel fibers to the surface of the coverslip. The density of such DNA stretched on the coverslips is high and for humans reaches to hundreds of genomes per coverslip.
6. Perform fluorescent hybridization on the coverslips. In view of the density of fibers, scanning and recording of the hybridized signal can be measured quickly.

REFERENCE:

Michalet X et al: Dynamic molecular combing: Stretching the whole human genome for high resolution studies. Science 277, 1518-1523, 1997