Wing circulatory organs in Drosophila

Why and how evolutionary novelties are introduced into a given body plan is crucial for our understanding of the morphological evolution of organisms. One of the mechanisms underlying this process is the recruitment of different components from various organ systems and their assembly to a novel functional unit. Based on our preliminary comparative anatomical studies we hypothesize that the cells which constitute the wing circulatory organs (WCO) of Drosophila are recruited from the dorsal vessel ("heart") of these animals during ontogenesis. In the proposed project we aim to verify this hypothesis by a combined developmental and genetic approach. In our investigations we have the great advantage of utilizing the only recently developed first tissue specific live cell marker, which is characterized by GFP expression in both the cardiac tissues and the cells of the WCO throughout development. This marker will be applied in our developmental approach for live cell imaging as well as complementary histological techniques to trace back the origin of the progenitor cells which give rise to the WCO, and to elucidate the developmental pathways underlying the process of WCO formation. In our genetic approach we will accomplish a large scale screening in selected mutant fly strains for phenotypes, which show alterations in the WCO formation or function, by visual scoring based on the GFP-marker. The subsequent identification of the corresponding genes will provide an excellent entry point to reveal the genetic pathways which are crucial for the development of the WCO and their function. Through this project we expect to obtain results highly relevant for the understanding of the development and genetics of the circulatory organs in the model organism Drosophila as well as a deeper insight into the processes involved in recruitment, and at a more general level, of the evolution of morphological novelties.

Why and how evolutionary novelties are introduced into a given body plan is crucial for our understanding of the morphological evolution of organisms. One of the mechanisms underlying this process is the recruitment of different components from various organ systems and their assembly into a novel functional unit. Based on our comparative anatomical studies we hypothesized that the cells which constitute the wing hearts of the well-known fruit fly Drosophila are recruited during development from the dorsal vessel ("heart"). In this project we aimed to verify this hypothesis by a combined developmental and genetic approach. In our project, we had the great advantage of utilizing a transgenic fly line, generated in the lab of our cooperation partner, in which both the heart and the cells of the wing hearts emit green light throughout the entire development when viewed under UV light. With this line we were able to analyze the development of the wing hearts in great detail. We found that the organs do not originate from heart muscle cells but from pericardial cells which are, in the classical view, counted among the cardiac mesoderm. This was surprising since pericardial cells normally do not form muscle tissue. Additionally, in a genetic approach we screened a collection of mutant fly lines for defects in wing heart development or function. With the help of these animals it was possible to identify genes required for wing heart development. Furthermore, we discovered a new biological function for wing hearts. During our project, we genetically generated flies without wing hearts. These animals indeed develop wings but are unable to fly. The same result was obtained in experiments where the wing hearts were destroyed by laser ablation. We were able to show that wing hearts suck the dying epidermal cells out of the wings at the end of wing development to enable tight bonding of the wing surfaces. In flies lacking wing hearts, the epidermal cells remain in the wings and prevent bonding of the wing surfaces. We assume that this is a general function of wing hearts in all insects.