Title: Analyzing Heterochromatin Formation Using Chromosome 4 of Drosophila melanogaster
Abstract: While chromosomes provide a broad level of genomicorganization within the nuclei of higher eukaryotes, thechromosome itself is further organized into multiple domains with distinct properties. This level of organizationis visible in interphase nuclei as areas of condensed heterochromatin and regions of more dispersed euchromatin. Chromatin domains are biochemically distinguished by the types of histone modification andassociated nonhistone chromosomal proteins. In mosthigher eukaryotes, domains of constitutive heterochromatin are normally restricted to pericentric and telomericDNA. A remarkable property of heterochromatin infungi, flies, and mammals is the ability to spread in cis, inresponse to loss of boundary constraints or to changes indosage or activity of chromatin components; this resultsin silencing of euchromatic genes that are abnormallyjuxtaposed to heterochromatic domains by chromosomerearrangement or transposition, referred to as Position Effect Variegation (PEV) (for review, see Grewal and Elgin2002). Recent studies in fungi and plants suggest that heterochromatin formation is targeted to repetitious elements through an RNAi mechanism, resulting in a domain of silenced chromatin (Volpe et al. 2002; Matzke etal. 2004; Schramke and Allshire 2004)...