This project analyzes the partitioning of the eye field in the Drosophila embryo. The eye field in the anterior neural plate of vertebrates and the head of the Drosophila embryo exhibit a high degree of similarity regarding the fate map of the visual system, and the signaling pathways controlling this fatemap. Drosophila counterparts of Shh (Hh), BMB4 (Dpp) and EGF, as well as Pax6, Six6 and many other regulatory genes all function in the Drosophila embryonic head. Preliminary data show that Dpp is secreted in the dorsal midline and forms a dorso-ventral gradient that specifies the different domains within the eye field. Dpp is then down-regulated in the eye field, except for its posterior boundary from where it may form a posterior-anterior gradient that partitions the visual primordium into larval and adult eye, and optic lobe. Hh is secreted at the lateral boundary of the eye field and may form a gradient that antagonizes the early Dpp gradient. Dr. Hartenstein and his research group will address the topology and morphogenesis of the Drosophila eye field and test their models of Dpp and Hh function in partitioning the eye field. The first aim is to reconstruct the details of the fate map, and to investigate the morphogenesis of the visual system. The second aim addresses the function of dpp in the eye field by investigating the dpp loss of function, heterotopic and heterochronic expression of dpp, activated Dpp receptor, and dominant negative Dpp receptor. In the third aim Dr. Hartenstein will analyze the role of Hh and its interaction with Dpp. The hypothesis will be tested that Hh negatively interacts with Dpp function. This would represent an interesting parallel to the vertebrate neural tube where ventral release of Shh also antagonizes BMPs secreted from dorsal tissue. By generating Dpp:hh double mutants and expressing mutant constructs the interaction of these genes in the embryonic head will be tested. In aim four Dr. Hartenstein will address the control of Dpp activity in the embryonic head. By establishing specific differences and similarities between early eye patterning in Drosophila and vertebrates, Dr. Hartenstein anticipates to furnish relevant information that helps interpreting Shh and BMP function in neural fate determination and to provide important insights in the evolution of the brain.
