Genome-wide features of neuroendocrine regulation in Drosophila by the basic helix-loop-helix transcription factor DIMMED

Abstract

Neuroendocrine (NE) cells use large dense core vesicles (LDCVs) to traffic, process, store and secrete neuropeptide hormones through the regulated secretory pathway. The dimmed (DIMM) basic helix-loop-helix transcription factor of Drosophila controls the level of regulated secretory activity in NE cells. To pursue its mechanisms, we have performed two independent genome-wide analyses of DIMM's activities: (i) in vivo chromatin immunoprecipitation (ChIP) to define genomic sites of DIMM occupancy and (ii) deep sequencing of purified DIMM neurons to characterize their transcriptional profile. By this combined approach, we showed that DIMM binds to conserved E-boxes in enhancers of 212 genes whose expression is enriched in DIMM-expressing NE cells. DIMM binds preferentially to certain E-boxes within first introns of specific gene isoforms. Statistical machine learning revealed that flanking regions of putative DIMM binding sites contribute to its DNA binding specificity. DIMM's transcriptional repertoire features at least 20 LDCV constituents. In addition, DIMM notably targets the pro-secretory transcription factor, creb-A, but significantly, DIMM does not target any neuropeptide genes. DIMM therefore prescribes the scale of secretory activity in NE neurons, by a systematic control of both proximal and distal points in the regulated secretory pathway.

Transcriptional Reorganization of Drosophila Motor Neurons and Their Muscular Junctions toward a Neuroendocrine Phenotype by the bHLH Protein Dimmed

“…Next we sought a link between Dimm and wingless signaling and noted that some direct targets of Dimm may be involved in exosome release (see Hadzic et al, 2015 ). The exosome-dependent release of Wg requires the transmembrane protein Evenness Interrupted (Evi) ( Koles et al, 2012 ).…”

“…The exosome-dependent release of Wg requires the transmembrane protein Evenness Interrupted (Evi) ( Koles et al, 2012 ). Two further proteins involved in Evi-exosome release, Rab11 and Ykt-6 ( Gross et al, 2012 ; Koles et al, 2012 ), were shown to be direct targets of Dimm ( Hadzic et al, 2015 ). Thus we tested effects of Dimm expression on Evi distribution in the NMJ.…”

“…Dimm confers a secretory phenotype to neuroendocrine cells that ensures increased capacity for neuropeptide production, storage, and release. This includes large cell bodies with well-developed endoplasmic reticulum and Golgi, enlarged storage capacity for neurosecretory vesicles associated with an upregulation of a host of specific proteins in the neuron ( Hewes et al, 2003 ; Hamanaka et al, 2010 ; Hadzic et al, 2015 ). One intriguing finding was that ectopic Dimm suppresses expression of small molecule neurotransmitters, thereby seemingly promoting a peptidergic secretory phenotype ( Hamanaka et al, 2010 ).…”

Drosophila carboxypeptidase D (SILVER) is a key enzyme in neuropeptide processing required to maintain locomotor activity levels and survival rate

“…The general requirement of CPs in neuropeptide and peptide hormone processing and the lack of a CPE gene in the Drosophila genome imply that dCPD is functionally important for the production of bioactive peptides in the fruit fly. This reasoning is supported by a prominent expression of svr in the central nervous system (CNS) and endocrine tissues such as the midgut (Chintapalli, Wang, & Dow, ), as well as by the direct transactivation of svr by the basic helix–loop–helix transcription factor DIMMED which confers a neuroendocrine peptidergic phenotype (Hadžić et al., ). Ectopic expression of svr transgenes in the neurohemal organ of the brain (corpora cardiaca) also affects processing of adipokinetic hormone (AKH; Sidyelyeva et al., ).…”

Drosophilacarboxypeptidase D (SILVER) is a key enzyme in neuropeptide processing required to maintain locomotor activity levels and survival rate

“…The general requirement of CPs in neuropeptide and peptide hormone processing and the lack of a CPE gene in the Drosophila genome imply that dCPD is functionally important for the production of bioactive peptides in the fruit fly. This reasoning is supported by a prominent expression of svr in the central nervous system (CNS) and endocrine tissues such as the midgut (Chintapalli, Wang, & Dow, 2007), as well as by the direct transactivation of svr by the basic helix-loophelix transcription factor DIMMED which confers a neuroendocrine peptidergic phenotype (Hadžić et al, 2015). Ectopic expression of svr transgenes in the neurohemal organ of the brain (corpora cardiaca) also affects processing of adipokinetic hormone (AKH; Sidyelyeva et al, 2010).…”