Normal brain functioning depends on the establishment of diverse cellular phenotypes. Our research program addresses the mechanisms that regulate differentiation of neuroendocrine cells during development. We use Drosophila molecular genetics to examine the biology of a basic HLH protein called DIMMED (DIMM). Our genetic studies indicate DIMM is necessary and sufficient to promote the cellular features that define neuroendocrine differentiation. First, DIMM is normally expressed by most of the principal peptidergic cells in Drosophila (though not all). Loss-of-function analysis indicates DIMM is not required for cell survival or growth, but is required for these cells to display a proper regulated secretory pathway and normal accumulation of neuropeptides. Gain-of-function studies indicate DIMM can activate the cellular machinery to support peptidergic function in non-peptidergic (i.e., conventional) neurons. At a molecular level, we have shown that DIMM is a transcription factor and that it activates several specific target genes. DIMM is related to the mammalian protein Mist1, a factor implicated in secretory cell differentiation. We hypothesize that DIMM is a dedicated, pro-secretory factor with conserved functions, whose study will lead to a better understanding of the organization and differentiation of neuroendocrine cell types. This research program supports efforts to address human syndromes caused by underlying neuroendocrine disorders, such as stress, or tumor formation in the pituitary or pancreas, and will help guide future programs of stem cell differentiation to generate specific neuroendocrine lineages in vitro. Here we propose five specific aims. First we will derive a consensus DIMM cis-binding site by analyzing in vitro and in vivo several direct target genes. Second, we will extend the list of molecular targets. Third, we will examine DIMM action mechanisms by genetically testing the roles of individual DIMM targets. Fourth, we will test the hypothesis that the paired homeoprotein Eyeless is the principal activator of dimmed. Finally, we will extend our analysis to the mouse model system by examining the hypothesis that the DIMM orthologue Mist1 plays an important role in mammalian peptidergic cell biology.

Public Health Relevance

We study the developmental mechanisms used by neurons to acquire their mature properties. This is significant because the proper functioning of the brain relies on the precision with which different categories of neurons are correctly assembled. In particular, we focus on peptidergic neurons that produce critical signals to coordinate normal physiology and behavior. Our work could help address diverse physiological, emotional and cognitive disorders.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Neurogenesis and Cell Fate Study Section (NCF)
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Mamounas, Laura
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Washington University
Schools of Medicine
Saint Louis
United States
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Park, Dongkook; Li, Peiyao; Dani, Adish et al. (2014) Peptidergic cell-specific synaptotagmins in Drosophila: localization to dense-core granules and regulation by the bHLH protein DIMMED. J Neurosci 34:13195-207
Mills, Jason C; Taghert, Paul H (2012) Scaling factors: transcription factors regulating subcellular domains. Bioessays 34:10-6
Park, Dongkook; Hadži?, Tarik; Yin, Ping et al. (2011) Molecular organization of Drosophila neuroendocrine cells by Dimmed. Curr Biol 21:1515-24
Hamanaka, Yoshitaka; Park, Dongkook; Yin, Ping et al. (2010) Transcriptional orchestration of the regulated secretory pathway in neurons by the bHLH protein DIMM. Curr Biol 20:9-18
Park, Dongkook; Taghert, Paul H (2009) Peptidergic neurosecretory cells in insects: organization and control by the bHLH protein DIMMED. Gen Comp Endocrinol 162:2-7
Park, Dongkook; Veenstra, Jan A; Park, Jae H et al. (2008) Mapping peptidergic cells in Drosophila: where DIMM fits in. PLoS One 3:e1896
Shafer, Orie T; Kim, Dong Jo; Dunbar-Yaffe, Richard et al. (2008) Widespread receptivity to neuropeptide PDF throughout the neuronal circadian clock network of Drosophila revealed by real-time cyclic AMP imaging. Neuron 58:223-37
Park, Dongkook; Shafer, Orie T; Shepherd, Stacie P et al. (2008) The Drosophila basic helix-loop-helix protein DIMMED directly activates PHM, a gene encoding a neuropeptide-amidating enzyme. Mol Cell Biol 28:410-21
Allan, Douglas W; Park, Dongkook; St Pierre, Susan E et al. (2005) Regulators acting in combinatorial codes also act independently in single differentiating neurons. Neuron 45:689-700
Park, Dongkook; Han, Mei; Kim, Young-Cho et al. (2004) Ap-let neurons--a peptidergic circuit potentially controlling ecdysial behavior in Drosophila. Dev Biol 269:95-108

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