| Alternative splicing is an importance source of transcriptome diversity. However, the extent to which alternative splicing has contributed to the lineage specific evolution of Drosophila species has not been previously assessed. Using comparative analysis, in a phylogenetic framework, and tiling array profiling, I performed a global analysis of alternative splicing differences among Drosophila species. Alternative splicing seems to evolve under strong selective constraint, with few changes between D. melanogaster and D. simulans, although changes do occur along D. pseudoobscura lineage. In contrast, changes in gene expression between species are more common than splicing differences.; It was further noticed that expression divergence is weakly correlated with sequence divergence at genic and 5' and 3' flanking regions, suggesting the distribution of regulatory elements might be very dispersed. X chromosome seems to be unique both in number of testis biased and species differential splicing events. The paucity of testis biased expression exons on the X is in agreement with the data on sex-biased expression and the prediction based on sexual antagonism. In contrast X-linked genes demonstrate faster rate of interspecies expression divergence and splicing difference than autosomal genes, suggesting expression changes in genic and exon level can be largely viewed as partial recessive beneficial mutations.; Another important factor contributing to genome evolution are lineage specific genes. Spx is a lineage-specific courtship gene in Drosophila melanogaster. The evolutionary process of spx has been associated with a high nucleotide substitution rate driven by positive Darwinian selection for a novel function. Yet, the 5' regulatory region of spx harbors an ancient sequence element that are conserved across Drosophilidae. Using green fluorescence protein transformation system, we demonstrated that this ∼200 bp conserved region is sufficient to drive spx expression across different tissues: brain, male accessory gland, wing (hair) and leg (bristle). Furthermore, the additional ∼800bp upstream of this core promoter region was able to enhance expression specifically in proboscis, suggesting the existence of enhancer elements. Using anti-GFP staining, we identified spx expression signal in brain antennal lobe and inner antennocerebral tract, suggesting that spx might be involved in olfactory neuron mediated regulation of male courtship behavior. |
