2.10 Glossary

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Antigenic Drift: is a mechanism for variation in viruses via the accumulation of mutations within the genes due to lack of proofreading capabilities and frequent proliferation that allows for selection of the most fit as well as evasion of the immune system.

Apoptosis: a form of programmed cell death that is often triggered by steps in transformation. In order for a cell to become cancerous it must gain the ability to evade apoptotic pathways. Oncogenes often mediate this process. 

Chromatin immunoprecipitation (ChIP): a technique that allows the relationship between a given protein and DNA to be investigated. It involves crosslinking chromatin in a whole cell lysate with its associated proteins, targeting the protein of interest with an antibody, shearing the DNA into fragments, and then using the antibody to precipitate the protein of interest out of solution, bringing its associated DNA fragment with it. This fragment can then be seperated from the protein and sequenced. This technique is useful in the identification of oncogenes and investigation of their function. 

Chromosomal rearrangement: a change in the structure of a chromosome due to the recombination of segments in novel ways, either within the same chromosome or to a non-homologous one. 

Chromosome inversion: a form of chromosomal rearrangement in which a segment of a chromosome has recombined in the opposite orientation as it was originially found.

Chromosome translocation: a form of chromosomal rearrangement in which non-homologous chromosomes have exchanged segments. 

DNA tumor viruses: viruses that can directly encode oncogenes. Viruses often carry genes that initiate the cell cycle and promote entrance into the S phase so that cellular DNA synthesis machinery becomes available for the virus to replicate its own genome. 

Epigenetics: the study of genetic modifications that control gene expression without changing the DNA sequence, through chromatin modifications such as DNA methylation and histone modifications.

Gene amplification: when a portion of the genome is duplicated, resulting in a higher than normal copy number of a certain gene. 

Insertion mutation: the addition of one or more bases to DNA. This can occur spontaneously or as a result of integration of foreign genetic material, such as a transposon or viral DNA. Insertion mutations can cause oncogene activation if the integration occurs near a proto-oncogene and results in its increased expression or alteration. 

Microarray: a microchip coated with single-stranded DNA sequences. When fragmented DNA or RNA from a sample of interest is washed over the chip, complimentary sequences within the sample will hybridize to specific locations on the chip, allowing the presence of a given gene to be detected. This technique is useful in the identification of oncogenes and oncogenic microRNAs. 

Oncogene: a gene that has the potential to cause transformation of a cell, often because it has acquired alterations causing it to be more active than normal or active at inappropriate times. See "proto-oncogene" below.

Oncogene activation: the transformation of a normal proto-oncogene into a cancer-causing oncogene. 

Point mutation: alteration of a single base of DNA.

Proto-oncogene: the normal version of an oncogene, present in all cells and contributing to healthy cellular functions in a regulated manner. They are often involved in the cell cycle and proliferation. Proto-oncogenes have the potential to become cancer-causing oncogenes if altered. 

Representation oligonucleotide microarray analysis (ROMA): a method which uses olionucleotdie probes to scan a genome of interest and determine gene copy numbers. This method can be useful in determining the presence of gene dulicaptions implicated with some oncogenes.

Retroviral oncogene: a retrovirus is a virus that reverse transcribes its RNA genome into DNA, which is then incorporated into the host cell genome. In some cases this incorporated DNA contains oncogenes which then cause transformation of the cell. 

Retrovirus: a virus with an RNA genome that is reverse transcribed into a DNA intermediate (the provirus), which is integrated into the host cell genome. The integration process is a form of insertional mutagenesis, which can randomly cause oncogene activation. 

Signal transduction: the process by which an extracellular signaling molecule is sensed by a receptor on a cell, which then triggers a series of responses to the signal. Key factors in signal transduction include growth factors (GFs), growth factor receptors (GFRs), and signal tranducers. Oncogene products are often involved in signal tranduction. 

Transcription factors (TFs): a large family of proteins that bind to regulatory regions of genes and control their expression.

Transdifferentiation: The conversion of a differentiated (non-stem) cell into a different type of differentiated cell.

Tumor suppressor gene: a gene that encodes proteins that negatively regulate cell proliferation and growth; a loss-of-function mutation would bring a cell one step closer to cancer.