Drosophila as a model for understanding development and disease

The fruit fly Drosophila melanogaster has proved to be an enduring model for biological research. First established as a genetic model over a hundred years ago by Thomas Hunt Morgan, it remains one of the most popular and powerful model organisms. Thanks to the continued efforts of the Drosophila research community, it now serves as a model not only for genetic research, but also for a diverse array of studies, ranging from investigations of basic cellular and molecular mechanisms to modeling human diseases. For this Special Issue, we invited Drosophila biologists to submit original research studies and technical advances that would be of interest to the broad readership of Developmental Dynamics. In addition, we invited several researchers to submit review articles in their areas of specialization. The collection of reviews and original research papers in this Special Issue highlight some of the continuing and exciting discoveries coming from Drosophila research. They emphasize the wide range of questions being addressed through Drosophila studies, and illustrate how the facility of combining diverse techniques, and developing new ones, is deployed in Drosophila to elucidate complex biological concepts. While Drosophila has long served as a model for basic biological research, more recently its potential as a model for unraveling molecular mechanisms of human diseases is becoming more widely appreciated, and we are fortunate to also have several articles and reviews that highlight this. As studies have revealed that cellular and molecular mechanisms of organogenesis are highly conserved, and Drosophila has functional homologs of nearly 75% of the human disease genes, we can anticipate that this aspect of Drosophila research will continue to expand. The accessibility and dispensability (for viability) of the eye, combined with its complex architecture and development, have made it among the most intensively studied organs in the fly. In this issue, Singh et al. (pages 69–84) review one of the earliest patterning steps during eye development, its subdivision into distinct dorsal and ventral compartments, explaining the mechanisms involved and their role in the growth and differentiation of the eye. The studies described give us an insight into how axial patterning facilitates the transition from a simple larval eye primordium into a complex threedimensional adult compound eye. Tsachaki and Sprecher (pages 40–56) provide a detailed summary of the molecular processes involved in specifying retinal cell types, beginning with the transcriptional networks involved in eye fate determination, through the patterning and signaling events that specify photoreceptor cells and assign them unique functions. Kumar (pages 136–149) focuses on cellular and genetic mechanisms that are deployed to construct the basic unit of the compound eye, the ommatidium. Terrell et al. (pages 215–228) provide an example of how Drosophila can be used as a model to explore the molecular functions of human homologues of Drosophila proteins, and to provide molecular insights into human genetic diseases. They use the fly eye as a model to examine the activities of three human genes, OTX1, OTX2, and CRX, along with variants of these genes associated with retinopathies. Drosophila has also been extensively used to address other aspects of