Heterochromatic genes in Drosophila: a comparative analysis of two genes
Sandra R Schulze 1, Bryant F McAllister 2, Donald A Sinclair 1, Kathleen A Fitzpatrick 1, Marcella Marchetti 3, Sergio Pimpinelli 3 and Barry M Honda 1*
1 Simon Fraser University
2 University of Iowa
3 U. Rome
* To whom correspondence should be addressed. E-mail: honda{at}sfu.ca.
Submitted on January 20, 2006
Revised on February 27, 2006
Accepted on 29 April 2006
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Abstract |
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Centromeric heterochromatin comprises ~30% of the Drosophila melanogaster genome, forming a transcriptionally repressive environment that silences euchromatic genes juxtaposed nearby. Surprisingly, there are genes naturally resident in heterochromatin, which appear to require this environment for optimal activity. Here we report an evolutionary analysis of two genes, Dbp80 and RpL15, which are adjacent in proximal 3L heterochromatin of D. melanogaster. DmDbp80 is typical of previously described heterochromatic genes: large, with repetitive sequences in its many introns. In contrast, DmRpL15 is uncharacteristically small. The orthologues of these genes were examined in D. pseudoobscura and D. virilis. In situ hybridization and whole genome assembly analysis show that these genes are adjacent, but not centromeric in the genome of D. pseudoobscura, while they are located on different chromosomal elements in D. virilis. Dbp80 gene organization differs dramatically among these species, while RpL15 structure is conserved. A bioinformatic analysis in five additional Drosophila species demonstrates active repositioning of these genes both within and between chromosomal elements. This study shows that Dbp80 and RpL15 can function in contrasting chromatin contexts on an evolutionary timescale. The complex history of these genes also provides unique insight into the dynamic nature of genome evolution.
Key Words:
Drosophila species, chromosome evolution, heterochromatin
