Laurel Raftery - US grants

Abstract Each cell independently interprets extracellular signals to decide its fate. An outstanding question in developmental biology is how these decisions are coordinated across the developing tissue primordium to produce a functional organ of appropriate size. Extracellular signals called morphogens are a critical mechanism to regulate cell fates across an entire primordium, and multiple morphogen signals are coordinated during development and in adult tissue self- renewal. The research proposed here will address interactions between morphogens in the transforming growth factor [unreadable] (TGF[unreadable]) family and those that stimulate the receptor tyrosine kinase (RTK) pathway. We will use genetic methods to investigate interactions in whole tissues, while the tiisue grows or reorganizes. The model genetic organism Drosophila is used, because of the low level of genetic redundancy and the powerful tools available for in vivo experiments. Within a cell, TGF[unreadable] signals are interpreted by Smad signal transduction pathways. We primarily focus on one class of TGF[unreadable] signals, the bone morphogenetic proteins (BMPs). Different levels of extracellular BMP activity stimulate different levels of nuclear Smads, thus determining the genes that are expressed. In addition, protein kinases stimulated by RTK signals can modulate the levels of nuclear Smads, which may alter the way that cells respond to BMP signals. Preliminary data suggest that RTK signals down-regulate the BMP- specific fly Smad Mad and the general fly Smad Medea. Aims 1 and 2 test the importance of this regulation during tissue growth and migration. Aim 3 will screen for new mechanisms that regulate BMP pathway activity upstream of Smads. The molecular components of these pathways are strongly conserved between flies and humans, so we anticipate that new mechanisms will be conserved as well. Thus, this work will be important to understand the underlying mechanisms associated with TGF[unreadable] dysfunction in human fibrosis, tumorigenesis, and vascular function.

LAY ABSTRACT:
Animals build and maintain functional organs throughout their lives. To build an organ, multiple steps occur as the embryo develops, both to make all the different types of cells needed for that organ, and to organize these different cells so that they can work together to perform the organ's function. A common strategy for organizing cells is through coordinated cellular movements and shape changes. This project aims to understand how each different kind of cell obtains the information it needs to move into the correct places and acquire the needed shape. This process requires that cells recognize each other, assess their current location in the developing tissue, and finally, use information from their environment and/or in their DNA blueprint to navigate through the tissue to the location where they are needed. To understand how cells manage this intricate dance, the investigator will study an example where cells organize to create an organlike structure that develops into a fruit fly egg. A series of precise cellular movements is needed to build the eggshell, which protects the developing embryo. Fly ovaries will be cultured and cell movements will be imaged through the microscope, using genetic and antibody assays to identify the specific proteins that cells use to interact with each other. These studies will be able to distinguish whether the major source of information for a cell's movements come from an internal program or from external environmental cues. The proteins and mechanisms identified will expand the knowledge of the cellular repertoire available to create organized structure in the many different types of organs observed across animal phyla. This research will provide essential scientific training for undergraduate and graduate students at the University of Nevada, Las Vegas. They will acquire important skills in teamwork, critical thinking, data management,as well as the needed skills to perform laboratory research.

TECHNICAL ABSTRACT:
The experiments of this proposal will examine the mechanisms by which a migrating sheet of cells can change its direction of migration. The work will focus on oogenesis of the fruit fly Drosophila melanogaster, to take advantage of sophisticated tools for genetic manipulations and new technologies for real-time, time-lapse imaging of cellular movements in ovary explants. Based on previous research, two models for the mechanisms that induce the change in direction will be contrasted; these models are not mutually exclusive. One model is that each cell decides independently to change its direction, through an intrinsic program of regulated gene expression in response to a bone morphogenetic protein (BMP) morphogen gradient. Experiments will test specific candidate transcriptional regulators for their requirements in the onset of specific phases of the new migration. The second model is that the cells respond to an extrinsic signal that reorients their direction or otherwise changes their migration behavior. This aspect of the project follows up on published reports that the BMP response system may use non-transcriptional mechanisms to induce changes in cell shape, as well as preliminary data that another signaling system is modulated in these cells. The investigator predicts that intrinsic gene regulation initiates the competence for a migration response, and that extrinsic signals orient the cells' migratory behaviors. This work will identify the molecular links between developmental gene regulatory networks and the cellular effectors that create the diverse array of functional architecture seen in tissues of multicellular organisms. In addition to these research activities, the investigator is collaboratively organizing a monthly Science Cafe (www.sciencecafes.org) to provide an interactive venue for local and regional scientists to discuss current scientific topics with the general Las Vegas community.

This project will investigate the effects of selection for starvation resistance on ovarian development in the fruitfly, Drosophila melanogaster. Starvation-resistant flies have survived many generations of laboratory-controlled starvation conditions, and are substantially larger than control flies, which were continuously supplied with food. The starvation-selected flies carry much more stored fat, in expanded fat tissues. In most insects, a larger female lays more eggs and therefore has more surviving offspring than a smaller female. This is not the case when large females from the starvation-resistant populations are compared to the smaller females from the control populations. This unexpected situation provides an excellent opportunity to look carefully at the tradeoffs between survival and reproduction, a central theme to the understanding of life cycles for many different species, and how they change during evolution. Because Drosophila melanogaster is a very well studied model organism, this project will use techniques of molecular genetics and cell biology to understand the underlying physiology and genetic changes that have occurred during starvation selection. The experimental toolkit available for Drosophila will be used to test the function of specific candidate genes in ovarian development and fat body function. This project will provide a unique learning environment for graduate students and undergraduates at a minority serving institution, by their participation in an integrated series of scientific activities that link evolutionary biology to developmental biology through an organismal perspective. Outreach activities will include production of videos displayed in the lobby of a highly-trafficked research building on the UNLV campus, participation in the NSF Radio 360 program, and development of a Science Café for the general public. The latter will consist of a monthly series of short presentations and discussions led by scientists and engineers from the UNLV community, government and industry.