Schulze Sandra R, McAllister Bryant F, Sinclair Donald A R, Fitzpatrick Kathleen A, Marchetti Marcella, Pimpinelli Sergio, Honda Barry M
Department of Molecular Biology snd Biochemistry, Simon Fraser University, Canada.
Genetics. 2006 Jul;173(3):1433-45. doi: 10.1534/genetics.106.056069. Epub 2006 Apr 30.
Centromeric heterochromatin comprises approximately 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 orthologs 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.
着丝粒异染色质约占黑腹果蝇基因组的30%，形成一种转录抑制环境，使附近并列的常染色质基因沉默。令人惊讶的是，异染色质中天然存在一些基因，它们似乎需要这种环境来实现最佳活性。在这里，我们报告了对两个基因Dbp80和RpL15的进化分析，它们在黑腹果蝇近端3L异染色质中相邻。DmDbp80是先前描述的异染色质基因的典型代表：基因很大，其许多内含子中有重复序列。相比之下，DmRpL15异常小。在拟暗果蝇和粗壮果蝇中研究了这些基因的直系同源基因。原位杂交和全基因组组装分析表明，这些基因在拟暗果蝇基因组中相邻，但不在着丝粒附近，而在粗壮果蝇中它们位于不同的染色体元件上。Dbp80基因组织在这些物种之间差异很大，而RpL15结构是保守的。对另外五个果蝇物种的生物信息学分析表明，这些基因在染色体元件内部和之间都有活跃的重新定位。这项研究表明，在进化时间尺度上，Dbp80和RpL15可以在不同的染色质环境中发挥作用。这些基因的复杂历史也为基因组进化的动态性质提供了独特的见解。
