Biomedical subjects

Dongkook Park

Publications and source records attributed to Dongkook Park.

5 recordsLinked to original sources

PubMed2005

Regulators acting in combinatorial codes also act independently in single differentiating neurons.

In the Drosophila ventral nerve cord, a small number of neurons express the LIM-homeodomain gene apterous (ap). These ap neurons can be subdivided based upon axon pathfinding and their expression of neuropeptidergic markers. ap, the zinc finger gene squeeze, the bHLH gene dimmed, and the BMP pathway are all required for proper specification of these cells. Here, using several ap neuron terminal differentiation markers, we have resolved how each of these factors contributes to ap neuron diversity. We find that these factors interact genetically and biochemically in subtype-specific combinatorial codes to determine certain defining aspects of ap neuron subtype identity. However, we also find that ap, dimmed, and squeeze additionally act independently of one another to specify certain other defining aspects of ap neuron subtype identity. Therefore, within single neurons, we show that single regulators acting in numerous molecular contexts differentially specify multiple subtype-specific traits.

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PubMed2004

Ap-let neurons--a peptidergic circuit potentially controlling ecdysial behavior in Drosophila.

Here we describe a novel set of peptidergic neurons conserved throughout all developmental stages in the Drosophila central nervous system (CNS). We show that a small complement of 28 apterous-expressing cells (Ap-let neurons) in the ventral nerve cord (VNC) of Drosophila larvae co-express numerous gene products. The products include the neuroendocrine-specific bHLH regulator called Dimmed (Dimm), four neuropeptide biosynthetic enzymes (PC2, Fur1, PAL2, and PHM), and a specific dopamine receptor subtype (dDA1). For the PC2, Fur1, and PAL2 enzymes, and for the dDA1 receptor, this neuronal pattern represents the vast majority of their total expression in the VNC. In addition, while Dimm and PHM are present in the peritracheal Inka cells in larvae, pupae, and adults, Ap, PC2, Fur1, PAL2, and dDA1 are not. PC2, PAL2, and DA1 receptor expression were all controlled by both dimm and ap. Previous genetic analysis of animals deficient in PC2 revealed an abnormal larval ecdysis phenotype. Together, these data support the hypothesis that the small cohort of Ap-let interneurons regulates larval ecdysis behavior by secretion of an unidentified amidated peptide(s). This hypothesis further predicts that the production of the Ap-let neuropeptide(s) is dependent on each of four specific enzymes, and that a certain aspect(s) of its production and/or release is regulated by dopamine input.

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PubMed2004

Drosophila uses two distinct neuropeptide amidating enzymes, dPAL1 and dPAL2.

Neuropeptide alpha-amidation is a common C-terminal modification of secretory peptides, frequently required for biological activity. In mammals, amidation is catalyzed by the sequential actions of two enzymes [peptidylglycine-alpha-hydroxylating monooxygenase (PHM) and peptidyl-alpha-hydroxyglycine alpha-amidating lyase (PAL)] that are co-synthesized within a single bifunctional precursor. The Drosophila genome predicts expression of one monofunctional PHM gene and two monofunctional PAL genes. Drosophila PHM encodes an active enzyme that is required for peptide amidation in vivo. Here we initiate studies of the two Drosophila PAL genes. dPAL1 has two predicted transmembrane domains, whereas dPAL2 is predicted to be soluble and secreted. dPAL2 expressed in heterologous cells is secreted readily and co-localized with hormone. In contrast, dPAL1 is secreted poorly, even when expressed with a cleaved signal replacing the predicted transmembrane domains; the majority of dPAL1 stays in the endoplasmic reticulum. Both proteins display PAL enzymatic activity. Compared to the catalytic core of rat PAL, the two Drosophila lyases have higher K(m) values, higher pH optima and similarly broad divalent metal ion requirements. Antibodies to dPAL1 and dPAL2 reveal co-expression in many identified neuroendocrine neurons. Although dPAL1 is broadly expressed, dPAL2 is found in only a limited subset of neurons. dPAL1 expression is highly correlated with the non-amidated peptide proctolin. Tissue immunostaining demonstrates that dPAL1 is largely localized to the cell soma, whereas dPAL2 is distributed throughout neuronal processes.

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PubMed2003

Identification and characterization of a G protein-coupled receptor for the neuropeptide proctolin in Drosophilamelanogaster.

Proctolin is a bioactive neuropeptide that modulates interneuronal and neuromuscular synaptic transmission in a wide variety of arthropods. We present several lines of evidence to propose that the orphan G protein-coupled receptor CG6986 of Drosophila is a proctolin receptor. When expressed in mammalian cells, CG6986 confers second messenger activation after proctolin application, with an EC(50) of 0.3 nM. In competition-based studies, the CG6986 receptor binds proctolin with high affinity (IC(50) = 4 nM). By microarray analysis, CG6986 transcript is consistently detected in head mRNA of different genotypes, and under different environmental conditions. By blot analysis, anti-CG6986 antibodies detect a band in tissue homogenates similar to the predicted size of the protein. Proctolin receptor immunosignals are found in the hindgut, heart, and in distinct neuronal populations of the CNS; such patterns correlate with previous demonstrations of proctolin biological activity, and in several instances, with areas of proctolin peptide immunosignals. The identification of a bona fide proctolin receptor provides the basis for a mechanistic analysis of this critical synaptic modulator.

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PubMed2003

The bHLH protein Dimmed controls neuroendocrine cell differentiation in Drosophila.

Neuroendocrine cells are specialized to produce, maintain and release large stores of secretory peptides. We show that the Drosophila dimmed/Mist1 bHLH gene confers such a pro-secretory phenotype on neuroendocrine cells. dimmed is expressed selectively in central and peripheral neuroendocrine cells. In dimmed mutants, these cells survive, and adopt normal cell fates and morphology. However, they display greatly diminished levels of secretory peptide mRNAs, and of diverse peptides and proteins destined for regulated secretion. Secretory peptide levels are lowered even in the presence of artificially high secretory peptide mRNA levels. In addition, overexpression of dimmed in a wild-type background produces a complimentary phenotype: an increase in secretory peptide levels by neuroendocrine cells, and an increase in the number of cells displaying a neuroendocrine phenotype. We propose that dimmed encodes an integral component of a novel mechanism by which diverse neuroendocrine lineages differentiate and maintain the pro-secretory state.

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