We have initiated the Drosophila Heterochromatin Genome Project (DHGP), as part of the Drosophila Genome Center (DGC) located at the Lawrence Berkeley National Labaratory in Berkeley, CA. The DHGP is funded by the National Human Genome Research Institute.
We are working to assemble, map, and annotate high-quality, 'finished' sequence for a large portion of Drosophila melanogaster heterochromatin. The quality of the annotation will be greatly improved by sequence finishing, additional full-length cDNA sequences of heterochromatic genes, comparisons with related sequences from other species, and optimization of strategies for annotating repeat-rich genomic sequences. The successful completion of these studies will produce tools and information that will aid future studies of heterochromatin structure, function, and evolution in Drosophila, and in other eukaryotes.
BACKGROUND
The division of chromosomes into euchromatic and heterochromatic regions is a highly conserved aspect of genome organization in multicellular eukaryotes. Heterochromatin comprises about 30% of the Drosophila melanogaster and human genomes. This enigmatic part of the genome has unusual cytological, molecular and genetic properties, including differential control of replication, condensation throughout the cell cycle, and the ability to silence gene expression.
In both flies and humans, heterochromatin is concentrated in large (Megabase-sized) blocks, predominantly in the centric and subtelomeric regions of all chromosomes. It contains tandemly-repeated short sequences (satellite DNAs, e.g. hundreds of kilobases of ...AAGAGAAGAG....), middle repetitive elements (e.g. transposable elements and ribosomal RNA genes), and some single-copy genes.
Heterochromatin is not inert, and is essential for cell and organismal viability in multicellular eukaryotes. Genes required for viability and fertility reside in heterochromatin, as are elements required for normal chromosomal inheritance. Heterochromatin plays an essential role in spindle attachment and chromosome movement (centromeres), meiotic pairing, and sister chromatid cohesion.
Although significant advances have been made in recent years in understanding heterochromatin structure and function, we know too little about the genomic sequences in the heterochromatin, the organization of these sequences, and their roles in essential biological functions.
