Each cell independently interprets extracellular signals to decide its fate. An outstandingquestion in developmental biology is how these decisions are coordinated across the developingtissue primordium to produce a functional organ of appropriate size. Extracellular signalscalled 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 thetransforming growth factor (TGF ) family and those that stimulate the receptor tyrosinekinase (RTK) pathway. We will use genetic methods to investigate interactions in wholetissues, 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 vivoexperiments. Within a cell, TGF signals are interpreted by Smad signal transductionpathways. We primarily focus on one class of TGF signals, the bone morphogenetic proteins(BMPs). Different levels of extracellular BMP activity stimulate different levels of nuclearSmads, thus determining the genes that are expressed. In addition, protein kinases stimulatedby RTK signals can modulate the levels of nuclear Smads, which may alter the way that cellsrespond 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 ofthis regulation during tissue growth and migration.
Aim 3 will screen for new mechanisms thatregulate BMP pathway activity upstream of Smads. The molecular components of thesepathways are strongly conserved between flies and humans, so we anticipate that newmechanisms will be conserved as well. Thus, this work will be important to understand theunderlying mechanisms associated with TGF dysfunction in human fibrosis, tumorigenesis,and vascular function.
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