Restriction landmark genomic scanning (RLGS) is a

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

analysis method for rapid simultaneous visualization of thousands of landmarks, or restriction sites. Using a combination of

restriction enzyme A restriction enzyme, restriction endonuclease, REase, ENase or'' restrictase '' is an enzyme that cleaves DNA into fragments at or near specific recognition sites within molecules known as restriction sites. Restriction enzymes are one class o ...

s some of which are specific to DNA modifications, the technique can be used to visualize differences in

methylation Methylation, in the chemistry, chemical sciences, is the addition of a methyl group on a substrate (chemistry), substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replac ...

levels across the

of a given organism. RLGS employs direct labeling of

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

, which is first cut by a specific series of restriction enzymes, and then labeled by a

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

(usually

phosphorus-32 Phosphorus-32 (32P) is a radioactive isotope of phosphorus. The nucleus of phosphorus-32 contains 15 protons and 17 neutrons, one more neutron than the most common isotope of phosphorus, phosphorus-31. Phosphorus-32 only exists in small quantiti ...

). A

two-dimensional A two-dimensional space is a mathematical space with two dimensions, meaning points have two degrees of freedom: their locations can be locally described with two coordinates or they can move in two independent directions. Common two-dimension ...

electrophoresis Electrophoresis is the motion of charged dispersed particles or dissolved charged molecules relative to a fluid under the influence of a spatially uniform electric field. As a rule, these are zwitterions with a positive or negative net ch ...

process is then employed, yielding high-resolution results. The radioactive second-dimension gel is then allowed to expose a large sheet of

film A film, also known as a movie or motion picture, is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, emotions, or atmosphere through the use of moving images that are generally, sinc ...

. The radiation produced by the radioactive labeling will cause the film to be exposed wherever the restriction fragments have migrated during electrophoresis. The film is then developed, yielding a visual representation of the results in the form of an

autoradiograph An autoradiograph is an image on an X-ray film or nuclear emulsion produced by the pattern of decay emissions (e.g., beta particles or gamma rays) from a distribution of a radioactive substance. Alternatively, the autoradiograph is also availab ...

. The same combination of restriction enzymes will produce the same pattern of 'spots' from samples from the same organisms, but different patterns for different types of organism. For example, human and mouse DNA will produce distinctly different patterns when treated with the same combination of enzymes. These finished auto-rads can be examined against each other, revealing any changes in gene expression that lead to visual differences in the film. Each autoradiograph contains thousands of spots, each corresponding to a labeled DNA restriction landmark. RLGS becomes useful when doing whole-genome scans, and can effectively do the work of thousands of

polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to make millions to billions of copies of a specific DNA sample rapidly, allowing scientists to amplify a very small sample of DNA (or a part of it) sufficiently to enable detailed st ...

s at once. It readily detects alterations deviating from normal, and thus is exceptionally effective in identifying hyper/hypomethylation in

tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

s, deletions or amplifications of genes, or simply changes in

gene expression Gene expression is the process (including its Regulation of gene expression, regulation) by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, proteins or non-coding RNA, ...

throughout the development of an organism.

Sources

* *http://www.informatics.jax.org/searches/accession_report.cgi?id=MGI:71287
a picture of an auto-rad from Roswell Park Comprehensive Cancer Center

References

{{reflist Molecular biology Laboratory techniques Genomics