A BMP-dependent feedback loop regulates dpp expression by direct and indirect mechanisms in the Drosophila wing imaginal disc Aldrich, Maryanna M creator 2012 xviii, 276 p. born digital Thesis (Ph.D. -- Brown University (2012) Wharton, Kristi Director McKeown, Michael Reader Freiman, Richard Reader Johnson, Mark Reader Raftery, Laurel Reader Brown University. BIOMED: Molecular Biology, Cell Biology, and Biochemistry sponsor theses Morphogen activity gradients assign positional information within fields of cells in a concentration-dependent manner. As transcriptional changes respond to signaling activity thresholds, cells must encounter a particular level of morphogen activity. As such, signal transduction pathways that behave as morphogens must have regulatory mechanisms in place to be robust and accommodate for signaling activity fluctuations. In the Drosophila wing imaginal disc, the BMP signaling pathway functions as a morphogen through the graded distribution of phosphorylated transducer, pMad. In this tissue, signaling through the ligand Dpp is important in generating the pMad gradient that directs transcription of target genes required for anterior-posterior patterning. Several mechanisms are known through which this pathway attains robustness; the work presented here identifies and characterizes an additional mechanism of transcriptional regulation of the ligand dpp. By examining dpp expression with increased or decreased BMP signaling levels, we have demonstrated that transcription of dpp within the medial wing pouch is regulated by a negative feedback loop. Mediated through canonical Mad-mediated BMP signaling, regulation of dpp occurs in a pMad dose-dependent manner. In the lateral wing pouch, BMP signaling has the ability to positively regulate expression of dpp, indicating a domain-specific dual role for BMP signaling in regulating dpp. By dissecting dpp's cis-regulatory sequences, we have revealed multiple enhancer regions that mediate feedback regulation of dpp. By testing specific binding sites and factors for a requirement in regulating dpp, we have determined that Mad plays a direct and indirect role in dpp regulation: directly, a Mad binding site influences dpp expression in the lateral wing pouch and, indirectly, a factor downstream of the Shn/pMad/Med repressor complex is required for negative feedback of dpp in the medial wing pouch. The transcription factor Ci is not required for negative regulation of dpp, despite its well-known role in determining the wing disc expression pattern of dpp. We propose that this negative feedback mechanism serves to "fine tune" BMP signaling and keep its activity levels within a normal range, accommodating for fluctuations in signaling output and ensuring robust signaling throughout development. BMP signaling dpp negative regulation Min jin dang (China)TranscriptionDrosophila RPB 20121023 engEnglish10.7301/Z0R49P2VIn CopyrightCollection is open for research.dissertations