Elucidating the evolution of embryonically expressed Drosophila melanogaster multigene families is crucial to a better understanding of metazoan development. These multigene families include essential components of various signal transduction pathways mandatory for proper embryogenesis. Two of these highly conserved pathways are the Wg/Wnt and TGF-beta pathways. In a molecular context, the evolutionary history of the Wg/Wnt pathway was elucidated and compared to the TGF-beta pathway. Whereas the TGF-beta pathway is characterized by many ancient gene duplications, analyses of the Wg/Wnt pathway revealed evidence for a number of gene duplication events unique to chordates. Further, differences in their receptor and signal transducer posttranslational modification regimes were found.

In a spatiotemporal context, the expression patterns of many additional multigene families expressed during D. melanogaster embryogenesis were also analyzed. To better study and quantify changes in gene expression, FlyExpress Release 4, an online resource containing the only digital library of standardized D. melanogaster embryos and computational tools for comparative expression pattern analysis, was developed. The FlyExpress resource was used to investigate the expression divergence of paralogous genes transcribed during D. melanogaster embryogenesis. Pairwise comparisons revealed a greater proportion of spatial compared to temporal divergence. Additionally, the contribution of spatial divergence varies across developmental stages, with duplicated genes showing an increasing refinement and divergence in spatial expression as development progresses. Paralogous D. melanogaster Wg/Wnt and TGF-beta pathway genes with in situ image data are largely consistent with overall expression trends found.