Position-effect variegation

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 1930.

Additional Selected References

 * 1) 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
 * 2) 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
 * 3) 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
 * 4) 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
 * 5) 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
 * 6) 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
 * 7) 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
 * 8) 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