Pattern formation and development of the visual system in Drosophila

Our laboratory focuses on two major developmental questions: The evolution of early embryonic development and the establishment of retinal and brain circuitry that underlies color vision. These two distinct systems represent paradigms for understanding how pattern formation is genetically controlled.

- The first project is an Evolution and Development (Evo-Devo) approach to the earliest steps of insect development, the formation of the antero-posterior embryonic axis. In flies, the morphogenetic gradient of the Bicoid protein is essential for anterior development.  However, bicoid is not conserved and is a newly evolved gene that has taken over the ancestral function performed by another more general system in other insects. We are using the wasp Nasonia as an alternate model system to study how a very distant species patterns its axis. Nasonia is a hymenopteran that diverged from dipterans over 200MY ago and does not have a bicoid gene. It exhibits a long germband mode of development that is very similar to that of flies: All segments form at the same time and the embryo occupies the entire length of the egg. In contrast, short germband insects such as Tribolium only generate a few head and thoracic segments that form in a small posterior part of the egg: all other segments are added later in a growth zone. This similarity with flies allows us to directly compare expression patterns with those of flies. Furthermore, the sequence of the Nasonia genome was recently completed and there are many early developmental mutants. Finally, parental RNAi is a very powerful technique to knock down gene function. We have shown that Nasonia, like flies, utilizes an anterior morphogenetic center to generate the patterning information required for the formation of all segments: flies have bcd mRNA localized at the anterior of the egg while Nasonia has localized otd mRNA, at both poles.  This represents a convergence of two distinct strategies to create the needed patterning information required for long germband development.  Our ongoing investigations attempt to understand the entire segmentation pattern in Nasonia, with the goal of reaching the same level of mechanistic detail as Drosophila in order to compare the two systems.