Position-effect variegation
Encyclopedia
Position-effect variegation is a variegation
caused by the inactivation of a gene
in some cells through its abnormal juxtaposition with heterochromatin
.
The classical example is the Drosophila
w[m4](speak white-mottled-4) translocation
. In this mutation
, an inversion
on the X chromosome
places the white gene next to pericentric heterochromatin. Normally, the white gene is expressed in every cell of the adult Drosophila eye resulting in a red eye phenotype
. In the w[m4] mutant the eye color is variegated (red-white mosaic colored) where the white gene is expressed in some cells in the eyes and not in others. The mutation was described first by Hermann Muller
in 1938.
Variegation
Variegation is the appearance of differently coloured zones in the leaves, and sometimes the stems, of plants. This may be due to a number of causes...
caused by the inactivation of a gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
in some cells through its abnormal juxtaposition with heterochromatin
Heterochromatin
Heterochromatin is a tightly packed form of DNA, which comes in different varieties. These varieties lie on a continuum between the two extremes of constitutive and facultative heterochromatin...
.
The classical example is the Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
w[m4](speak white-mottled-4) translocation
Chromosomal translocation
In genetics, a chromosome translocation is a chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes. A gene fusion may be created when the translocation joins two otherwise separated genes, the occurrence of which is common in cancer. It is detected on...
. In this mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
, an inversion
Chromosomal inversion
An inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end. An inversion occurs when a single chromosome undergoes breakage and rearrangement within itself. Inversions are of two types: paracentric and pericentric.Paracentric inversions do not include the...
on the X chromosome
X chromosome
The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals and is common in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system...
places the white gene next to pericentric heterochromatin. Normally, the white gene is expressed in every cell of the adult Drosophila eye resulting in a red eye phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
. In the w[m4] mutant the eye color is variegated (red-white mosaic colored) where the white gene is expressed in some cells in the eyes and not in others. The mutation was described first by Hermann Muller
Hermann Müller
Hermann Müller may refer to:* Hermann Müller , German botanist with whom Darwin corresponded* Hermann Müller , Swiss botanist...
in 1938.
Selected References
- Aagaard, L., G. Laible, P. Selenko, M. Schmid, R. Dorn, G. Schotta, S. Kuhfittig, A. Wolf, A. Lebersorger, P. B. Singh, G. Reuter, and T. Jenuwein. 1999. "Functional mammalian homologues of the Drosophila PEV-modifier Su(var)3- 9 encode centromere-associated proteins which complex with the heterochromatin component M31". Embo J 18:1923-38. PMID 10202156
- Buchner, K., P. Roth, G. Schotta, V. Krauss, H. Saumweber, G. Reuter, and R. Dorn. 2000. "Genetic and molecular complexity of the position effect variegation modifier mod(mdg4) in Drosophila". Genetics 155:141-57. PMID 10790390
- Dorn, R., V. Krauss, G. Reuter, and H. Saumweber. 1993. "The enhancer of position-effect variegation of Drosophila, E(var)3-93D, codes for a chromatin protein containing a conserved domain common to several transcriptional regulators". Proc Natl Acad Sci U S A 90:11376-80. PMID 8248257
- Ebert, A., G. Schotta, S. Lein, S. Kubicek, V. Krauss, T. Jenuwein, and G. Reuter. 2004. "Su(var) genes regulate the balance between euchromatin and heterochromatin in Drosophila". Genes Dev 18:2973-83. PMID 15574598
- Eissenberg, J. C., G. D. Morris, G. Reuter, and T. Hartnett. 1992. "The heterochromatin-associated protein HP-1 is an essential protein in Drosophila with dosage-dependent effects on position-effect variegation". Genetics 131:345-352. PMID 1644277
- Jenuwein, T., G. Laible, R. Dorn, and G. Reuter. 1998. "SET domain proteins modulate chromatin domains in eu- and heterochromatin". Cell Mol Life Sci 54:80-93. PMID 9487389
- Schotta, G., A. Ebert, V. Krauss, A. Fischer, J. Hoffmann, S. Rea, T. Jenuwein, R. Dorn, and G. Reuter. 2002. "Central role of Drosophila SU(VAR)3-9 in histone H3-K9 methylation and heterochromatic gene silencing". Embo J 21:1121-31. PMID 11867540
- Tschiersch, B., A. Hofmann, V. Krauss, R. Dorn, G. Korge, and G. Reuter. 1994. "The protein encoded by the Drosophila position-effect variegation suppressor gene Su(var)3-9 combines domains of antagonistic regulators of homeotic gene complexes". Embo J 13:3822-31. PMID 7915232