This project aims to define the basic molecular mechanisms of Hedgehog (Hh) signal transduction in Drosophila. Hh is one of only a few families of extracellular signaling molecules responsible for directing development and regulating stem cell activity in Drosophila and in humans. Consequently, genetic alterations to Hh signaling underlie many developmental disorders and many types of cancer. Pioneering studies in Drosophila identified the central Hh signaling pathway components, which were later found to be highly conserved in mammals. Those advances led to much improved diagnosis of several human syndromes and diseases, and to the development of very promising anti-cancer drugs that target Smoothened (Smo), a key membrane protein that initiates Hh signal transduction. The Hh pathway culminates in altering patterns of gene transcription by modifying the activity of the conserved transcription factors, Ci (in flies) and Gli1-3 (in mammals). Deciphering the mechanisms that connect Smo to Ci/Gli activation is critical to understand Hh signaling and for the development of drugs that directly target Ci/Gli activity. Such drugs would potentially counter pathway activation by any type of oncogenic mutation. Hh signaling is extremely sensitive to the stoichiometry of signal transduction components and must therefore be studied under normal physiological conditions. Drosophila offers the most rapid and incisive molecular genetic approaches to accomplish this. New insights can then be applied rapidly to Hh signaling in humans and other mammals because the components and mechanisms involved are highly conserved. This project seeks to understand how full-length Ci (Ci-155) is activated and how this is integrated with regulation of Ci-155 levels to produce appropriate dose-dependent activation of Hh target genes in Drosophila. One key factor facilitating these objectives is our discovery of the central role of the protein kinase, Fused (Fu) in activating Ci. Hence, one set of aims is to discover the direct target for Fu and how this activates Ci-155. A second key factor is our recent development of genomic transgenes and an efficient gene replacement strategy to investigate the activity of Ci variants expressed at physiological levels. This approach is essential to identify the sites of interaction and ultimate impact of all regulatoy inputs into the terminal effector of Hh signaling. It will be used to study the regulation of Ci-15 levels by proteolytic mechanisms and the regulation of Ci-155 activity by Fu and other central pathway components, Costal 2, Protein Kinase A and Suppressor of fused.

Public Health Relevance

Many birth defects and a wide spectrum of highly prevalent cancers arise from aberrant regulation of the Hedgehog signaling pathway. Most components of this pathway were first discovered in Drosophila and then found to have equivalent roles in mammals, leading to improved diagnoses of human disease and the development of promising anti-cancer drugs. Further progress in addressing these health issues will be spurred by a deeper understanding of the mechanism of Hedgehog signaling, gained from the continued genetic analysis in Drosophila outlined in this project.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Development - 2 Study Section (DEV2)
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Melillo, Amanda A
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Columbia University (N.Y.)
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New York
United States
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Garcia-Garcia, Elisa; Little, Jamie C; Kalderon, Daniel (2017) The Exon Junction Complex and Srp54 Contribute to Hedgehog Signaling via ci RNA Splicing in Drosophila melanogaster. Genetics 206:2053-2068
Zadorozny, Eva V; Little, Jamie C; Kalderon, Daniel (2015) Contributions of Costal 2-Fused interactions to Hedgehog signaling in Drosophila. Development 142:931-42
Marks, Steven A; Kalderon, Daniel (2011) Regulation of mammalian Gli proteins by Costal 2 and PKA in Drosophila reveals Hedgehog pathway conservation. Development 138:2533-42
Zhou, Qianhe; Kalderon, Daniel (2011) Hedgehog activates fused through phosphorylation to elicit a full spectrum of pathway responses. Dev Cell 20:802-14
Gleason, Julie E; Eisenmann, David M (2010) Wnt signaling controls the stem cell-like asymmetric division of the epithelial seam cells during C. elegans larval development. Dev Biol 348:58-66
Zhou, Qianhe; Kalderon, Daniel (2010) Costal 2 interactions with Cubitus interruptus (Ci) underlying Hedgehog-regulated Ci processing. Dev Biol 348:47-57
Vied, Cynthia; Kalderon, Daniel (2009) Hedgehog-stimulated stem cells depend on non-canonical activity of the Notch co-activator Mastermind. Development 136:2177-86
Smelkinson, Margery G; Zhou, Qianhe; Kalderon, Daniel (2007) Regulation of Ci-SCFSlimb binding, Ci proteolysis, and hedgehog pathway activity by Ci phosphorylation. Dev Cell 13:481-95
Zhou, Qianhe; Apionishev, Sergey; Kalderon, Daniel (2006) The contributions of protein kinase A and smoothened phosphorylation to hedgehog signal transduction in Drosophila melanogaster. Genetics 173:2049-62
Smelkinson, Margery G; Kalderon, Daniel (2006) Processing of the Drosophila hedgehog signaling effector Ci-155 to the repressor Ci-75 is mediated by direct binding to the SCF component Slimb. Curr Biol 16:110-6

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