Washington University in St. Louis
Campus Box 1137
One Brookings Drive
St. Louis, MO 63130-4899
We are interested in the role that chromatin structure plays in gene regulation, both effects from packaging large domains and local effects of the nucleosome array. Working with Drosophila melanogaster, we have used a transposable P element containing a copy of the white gene, a visible marker for gene silencing, and a copy of hsp26, a well-characterized inducible gene, to examine the effect of insertion into different chromosomal domains. While these genes are fully active in euchromatic domains, silencing (similar to Position Effect Variegation) is observed on insertion into pericentric heterochromatin, telomeres, and sites within the small fourth chromosome. Both changes in the local nucleosome array, and the spatial organization of the nucleus, appear critical in determining gene silencing. The fourth chromosome, which appears entirely heterochromatic by many criteria, but has ~80 genes, is the focus of our studies. Mapping experiments indicate that heterochromatin formation can be targeted by the presence of a repetitious element, 1360, and perhaps by other similar elements. Genetic analysis has shown that heterochromatic silencing is dependent on the RNAi machinery. Work is ongoing to determine the mechanism of heterochromatin targeting, and to analyze the role of critical heterochromatin-associated proteins, including HP1 and HP2.
Photo caption: Our P-element construct contains a visible marker for variegation, hsp70-white, and a marked copy of hsp26 for accompanying studies of chromatin structure. Many fly lines have been recovered showing a PEV phenotype (A); all have P element inserts in the pericentric heterochromatin (as shown for this case by in situ hybridization of the polytene chromosomes with the entire P element; see B), telomeres and the small fourth chromosome.
Kharchenko PV, Alekseyenko AA, Schwartz YB, Minoda A, Riddle NC, Ernst J, Sabo PJ, Larschan E, Gorchakov AA, Gu T, Linder-Basso D, Plachetka A, Shanower G, Tolstorukov MY, Luquette LJ, Xi R, Jung YL, Park R, Bishop EP, Canfield TP, Sandstrom R, Thurman RE, MacAlpine DM, Stamatoyannopoulos J, Kellis M, Elgin SCR, Kuroda MI, Pirrotta V, Karpen G, Park PJ. Comprehensive analysis of the chromatin landscape in Drosophila melanogaster. Nature. 2011 471: 480-5. PMCID: PMC3109908
Riddle NC, Minoda A, Kharchenko PV, Alekseyenko AA, Schwartz YB, Tolstorukov MY, Gorchakov AA, Kennedy C, Linder-Basso D, Jaffe JD, Shanower G, Kuroda MI, Pirrotta V, Park PJ, Elgin SCR, Karpen GH. Plasticity in patterns of histone modifications and chromosomal proteins in the Drosophila heterochromatin. Genome Res. 2011 21:147-63. PMID: 21177972
Brower-Toland B, Riddle NC, Jiang H, Huisinga KL and Elgin SCR. Multiple SET methyltransferases are required to maintain normal heterochromatin domains in the genome of Drosophila melanogaster. Genetics. 2009 181: 1303-19. PMID: 19189944 PMCID: PMC2666501
Riddle NC, Leung W, Haynes KA, Granok H, Wuller J and Elgin SCR. An investigation of heterochromatin domains on the fourth chromosome of Drosophila melanogaster. Genetics. 2008 178: 1177-1191. PMID: 18245350 PMCID: PMC2278077
Haynes KA, Caudy AA, Collins L and Elgin SCR. Element 1360 and components of the RNAi system contribute to HP1-dependent silencing of a pericentric reporter. Current Biol. 2006 16: 2222-2227. PMID: 17113386 PMCID: PMC1712676
Shaffer C, Cenci G, Thompson B, Stephens GE, Slawson E, Adu-Wusu K, Gatti M, and Elgin SCR. The largo isoform of Drosophila melanogaster Heterochromatin Protein 2 plays a critical role in gene silencing and chromosome structure. Genetics. 2006 174: 1189-1204. PMID: 16980400 PMCID: PMC1667101.