The Drosophila salivary gland (SG) is an ideal model for revealing the molecular and cellular events underlying formation and physiological specialization of epithelial tubular organs, such as the lungs, kidneys, and secretory glands of humans. The SG is a simple tubular organ that forms using the same morphogenetic changes as more complicated organs of higher animals, including changes in cell shape, adhesion and movement. The SG is also the largest secretory organ in the embryo providing an ideal model for how cells achieve high-level secretory capacity and how changes in capacity are coordinated with the expression of secretory content. We have discovered four key transcription factors that play major roles in the morphogenesis and physiological specialization of the SG, and we have identified many/most of their transcriptional targets using genome-wide approaches. In this proposal, we explore how these proteins function both independently and as part of larger complexes to regulate distinct aspects of epithelial tube development.
In Specific aim #1, we use genome-wide in vivo DNA binding assays to test our model that the levels of expression of SG specific gene products is mediated through the coordinate binding of three key transcription factors ? Fkh, the Drosophila FoxA orthologue, Sage, a less highly conserved bHLH protein expressed in only the SG, and Sens, a zinc-finger transcription factor whose SG expression requires Fkh and Sage. We ask if CrebA, a bZip transcription factor that increases secretory capacity, also boosts levels of SG target gene expression directly or indirectly. We will identify binding sites for each protein, both in WT SGs and in SGs mutant for each other transcription factor. The biological relevance of specific cis acting sites will be validated in a representative subset of known target genes. These studies will reveal if we have identified the major factors controlling SG gene expression, and tests mechanistic models of enhancer organization and function in a system where the key major players and their downstream targets are known and can be manipulated.
In Specific aims #2 and #3, we focus on the Sage, Sens and CrebA ? independent functions of Fkh in controlling formation of epithelial tubes. We have identified Fkh target genes that when mutant disrupt early stages of tube morphogenesis. We ask how the products of these early Fkh target genes interface with membrane and cytoskeletal proteins to coordinate changes in cell shape and arrangement during tube internalization. We further use the Fkh binding data from aim #1 to identify additional key morphogenetic regulators.

Public Health Relevance

To understand how organs normally form during early development, we study formation of a model organ in a model organism: the salivary gland in the fruitfly Drosophila melanogaster. Our studies will reveal how regulatory molecules that are conserved from flies to humans control both organ architecture and physiology. The relatively smaller costs, quicker developmental time, and accessibility to a wide range of tools, makes the fly salivary gland an expedient model for uncovering key developmental mechanisms.

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National Institute of Dental & Craniofacial Research (NIDCR)
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Development - 1 Study Section (DEV1)
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Chander, Preethi
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Johns Hopkins University
Anatomy/Cell Biology
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Wells, Michael B; Villamor, Jordan; Andrew, Deborah J (2017) Salivary gland maturation and duct formation in the African malaria mosquito Anopheles gambiae. Sci Rep 7:601
Chung, SeYeon; Kim, Sangjoon; Andrew, Deborah J (2017) Uncoupling apical constriction from tissue invagination. Elife 6:
Manning, Lathiena; Sheth, Jinal; Bridges, Stacey et al. (2017) A hormonal cue promotes timely follicle cell migration by modulating transcription profiles. Mech Dev 148:56-68
Hanlon, Caitlin D; Andrew, Deborah J (2016) Drosophila FoxL1 non-autonomously coordinates organ placement during embryonic development. Dev Biol 419:273-284
Fox, Rebecca M; Andrew, Deborah J (2015) Changes in organelle position and epithelial architecture associated with loss of CrebA. Biol Open 4:317-30
Wells, Michael B; Andrew, Deborah J (2015) ""Salivary gland cellular architecture in the Asian malaria vector mosquito Anopheles stephensi"". Parasit Vectors 8:617
Hanlon, Caitlin D; Andrew, Deborah J (2015) Outside-in signaling--a brief review of GPCR signaling with a focus on the Drosophila GPCR family. J Cell Sci 128:3533-42
Fox, Rebecca M; Andrew, Deborah J (2015) Transcriptional regulation of secretory capacity by bZip transcription factors. Front Biol (Beijing) 10:28-51
Andrew, Deborah J; Yelon, Deborah (2015) Editorial overview: Developmental mechanisms, patterning and organogenesis. Curr Opin Genet Dev 32:v-viii
Chung, Seyeon; Andrew, Deborah J (2014) Cadherin 99C regulates apical expansion and cell rearrangement during epithelial tube elongation. Development 141:1950-60

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