Maternal Control of Pattern Formation at the Ends of the Drosophila Embryo

University Of Texas At Austin, Austin TX

Investigators

Abstract

Project Summary The mechanisms through which the seemingly simple fertilized egg generates a complex multicellular organism is a topic of fundamental interest that has been pondered since the time of Aristotle. A major insight that has emerged from studies of early development in the fruitfly Drosophila melanogaster is that the generation of pattern in the embryo is dependent upon the prior establishment of pattern in the ovarian follicle in which the egg is formed. The mother fly provisions the developing egg with a set of localized determinants that will later direct the spatially- specific expression of the embryo's own genes. Among the structures that are specified by localized maternal determinants are the most terminally-positioned structures of the Drosophila embryo, the acron at the anterior and the telson at the posterior. Formation of the termini requires activation of the transmembrane receptor tyrosine kinase Torso, which is distributed throughout the membrane of the early embryo. This activation must occur specifically at the ends of the embryo. The ligand for Torso is thought to be the Trunk protein, which is secreted into the fluid-filled perivitelline space that lies between the embryonic membrane and the inner surface of the eggshell, the vitelline membrane. Spatially-restricted activation of Torso by Trunk is believed to be controlled by the product of the gene torsolike. During oogenesis, torsolike is expressed in two specialized groups of polar follicle cells at the anterior and posterior ends of the developing oocyte. Our laboratory has found that Torsolike is localized to the anterior and posterior ends of the eggshell. These observations suggest a mechanism whereby an inactive precursor form of Trunk is secreted uniformly into the perivitelline space and processed into an active ligand specifically at the ends of the egg where it then binds and activates the Torso receptor. Trunk activation requires the function of Torsolike in a process that has not been elucidated. The objectives of this work are to determine the molecular mechanism by which Trunk becomes activated, and to elucidate the role Torsolike protein plays in this process. The specific aims are: (1) To determine whether Trunk is processed from an inactive precursor into an active ligand. (2) To identify other effector molecules involved in the formation of the Trunk ligand by their abilities to interact with Torsolike, and through the characterization of new mutations that affect the specification of the termini. (3 ) To identify the determinants of Torsolike that mediate its localization in the vitelline membrane of the eggshell. Intellectual merit: In addition to their contribution to the understanding of pattern formation in early development these experiments have significance outside of the context of Drosophila early development. Signal transduction through receptor tyrosine kinases is required for a wide variety of cell/cell communication pathways that operate in numerous physiological and developmental contexts, including axonal pathfinding, cell migration, cell differentiation and proliferation. The role of the Drosophila Torso receptor in embryonic patterning is a particularly compelling paradigm because of the exquisite regulation of its activation, both spatially and temporally. The control of Torso activation by its ligand is likely to provide important insights applicable to a variety of other ligand/receptor interactions that are of intellectual, as well as medical interest. Broader impacts resulting from the proposed activity: (1) Discovery, understanding, teaching, training and learning. The maternal control of Drosophila embryonic anterior-posterior polarity is a textbook paradigm that is used in undergraduate teaching of developmental biology. The experiments described herein seek a deeper understanding of this process. Furthermore, the investigations proposed provide numerous opportunities for experimental contributions by undergraduate students at the University of Texas, which will contribute to "hands on" training of those students in a research setting. Interested undergraduate students will be encouraged to participate in this project. These students will have the opportunity to present their work at local and national scientific meetings. Both the graduate student researcher and faculty associates comprising the research team on this proposal will also engage in undergraduate teaching. (2) Participation of underrepresented groups. The University of Texas matriculates a large population of students from historically underrepresented groups. Opportunities for hands on training in laboratory research related to the proposed studies will be available to interested students from these groups. (3) Dissemination of Results. Results obtained will be published in the scientific literature and reported at scientific conferences. Moreover, segments of the proposed investigations involve the generation of reagents likely to be of use to other investigors. These will be disseminated freely to any who request them.