Novel Regulation of Pattern Formation in Drosophila

Duke University, Durham NC

Investigators

Abstract

The fruitfly, Drosophila, is easy to manipulate in the laboratory and can be used to discover genes that control the growth and shaping of animal embryos. Flies are fed a chemical that causes mutations in the DNA, the progeny are bred and then examined for altered development of the fly. A mutation that breaks an essential gene will cause dramatic changes in the body pattern. Many of the fly genes identified this way have human counterparts, which perform very similar functions during human development. The Bejsovec laboratory uses this strategy to study the inner workings of a genetic pathway that is shared between flies and humans. This pathway, triggered by the Wg/Wnt growth factor, tells cells where they are in the body and what special structure to become; inappropriate re-activation of the Wnt pathway in adult tissues is associated with human cancers. The Bejsovec lab has found that three genes already known to work together to control cell division, have a second unexpected function in controlling the Wnt pathway. This project will determine how these genes exert control over the pathway, and how their action disrupts the fly body plan. Broader impacts of the project include deeper understanding of developmental mechanisms in all animal species, and a hands-on research experience for undergraduate and high school students in the Bejsovec laboratory and for undergraduates in an existing laboratory course. Although the Wg/Wnt pathway plays a central role in development and tissue homeostasis, the sequence of events, from Wg/Wnt binding at the cell surface to the downstream activation of target genes, is still not completely understood. Tumbleweed (Tum), Pavarotti (Pav) and Pebble (Pbl) repress Wg/Wnt pathway activity in cultured human cells and in fly embryos. These genes may represent a crucial missing link, perhaps missed in earlier screens for Wg/Wnt pathway components because all three genes have essential functions in cell division. In cytokinesis, Tum and Pav position Pbl-RhoGEF at the equator to activate the G protein, Rho, which organizes the actin contractile ring. Work proposed here will determine whether (and how) Tum, Pav, and Pbl make contact with known Wg/Wnt components, and will test whether GTPase activation is involved. In addition, reducing Tum or Pbl function in adult precursor cells creates a novel homeotic transformation which may result from the simultaneous disruption of cell signaling and cell division. Genetic and molecular tools available in Drosophila will be used to determine how misregulation of signaling and/or cytokinesis might alter segmental identity. The resulting data will provide insight into Wg/Wnt pathway control and tissue patterning, and may reveal new connections between cell division and cell fate specification during development. The unique appearance of the transformed flies will appeal to undergraduate and high school students, engaging them in the scientific enterprise and helping to recruit a diverse group, including women, socioeconomically disadvantaged and underrepresented minority students, into the workforce.