Transcription profiling by array of D. ananassae, D. melanogaster, D. persimilis, D. pseudoobscura, D. simulans, D. virilis embryogenesis to investigate gene expression

The observation that animal morphology tends to be conserved during the embryonic phylotypic period led to the proposition that embryogenesis diverges more extensively early and late than in the middle, known as the hourglass model. This pattern of conservation is thought to reflect a major constraint on the evolution of animal body plans. Despite a wealth of morphological data confirming that there is often remarkable divergence in the early and late embryos of species from the same phylum, it is not yet known to what extent gene expression evolution, which plays a central role in the elaboration of different animal forms, underpins the morphological hourglass. Here we address this question using species-specific microarrays designed from six sequenced Drosophila species. Although it is generally appreciated that gene expression divergence plays a key role in the evolution of morphological diversity, no studies to date have addressed the extent to which expression divergence underpins the hourglass pattern at the genome-wide level. We test the molecular basis of the hourglass model of developmental evolution using gene expression data from six Drosophila species with sequenced genomes (D. ananassae, D. melanogaster, D. persimilis, D. pseudoobscura, D. simulans, and D. virilis) thereby enabling unambiguous quantitative comparisons across orthologous genes for a set of species separated by up to 40 million years. Gene expression levels were measured for 3019 genes, known to be expressed during embryonic development from RNA in situ data, at 2 hour intervals for the majority of embryogenesis using a microarray time-course with three biological replicates per species and four species-specific probes per gene.