The bHLH protein Dimmed controls neuroendocrine cell differentiation inDrosophila

Abstract

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. 1772 dimmed (dimm), with an expression pattern that corresponds precisely to the neuronal and endocrine cells that accumulate large amounts of secretory peptides. We present both loss-offunction and gain-of-function analyses to argue that dimm confers a pro-secretory phenotype within these diverse cells, and that its actions appear confined to that aspect of cellular differentiation. Thus, we propose a novel and general mechanism, of which dimm is an essential component, for the amplification of the regulated secretory pathway by dedicated secretory cells. MATERIALS AND METHODS StrainsFlies were cultured at 22-25°C on a standard cornmeal-yeast-agar medium. The molecular and genetic characterization of c929, R6 and Rev8 has been described previously (Hewes et al., 2000). Rev4 and Rev18 are X-ray revertants of P{PZ}l (2)k05106 S2a ) were obtained by transposase-mediated excision, and each line was characterized by PCR with primers flanking the original insertion site. Except as noted, all other strains are described elsewhere (Lindsley and Zimm, 1992;FlyBase, 1999) and were obtained from the Bloomington stock center, the BDGP Gene Disruption Project and other sources. Scoring of dimm larvaeEggs were collected on apple juice-agar plates supplemented with yeast paste. Larvae were collected from the plates, and heterozygotes (y* w* and balanced over CyO-y + ) were distinguished by mouthpart color. After scoring, size-matched pairs of y -and y + larvae were dissected and stained in parallel.

Vesicle capture, not delivery, scales up neuropeptide storage in neuroendocrine terminals

“…As newly made peptides can be released preferentially (21,24), transcriptional regulation that alters DCV content can change the mixture of neuropeptides released at the nerve terminal. Second, DCV capture is itself increased by the transcription factor DIMM, which was known to increase the accumulation of neuropeptidecontaining DCVs in central neurons (10,13). Presumably, DIMM induces a gene encoding for a presynaptic DCV capture effector, which might be regulated by kinases and G proteins (25,26).…”

“…The transcription factor DIMM regulates the capacity to accumulate amidated neuropeptide-containing DCVs in a subpopulation (∼3%) of Drosophila neurons without regulating neuropeptide gene expression (10)(11)(12)(13)22). Although this could be assumed to reflect an effect on DCV synthesis that is not cargo-specific, the above results from type Ib and III boutons suggested the alternative possibility that DIMM promotes DCV capture.…”

“…Furthermore, transcriptional networks specify peptidergic neurons in Drosophila and mammals (e.g., [3][4][5][6][7][8][9]. Finally, accumulation of amidated neuropeptides and DCVs in Drosophila neurons is enhanced by the transcription factor Dimmed (DIMM) (10)(11)(12)(13). Indeed, DIMM induces DCVs in photoreceptors that do not normally possess these organelles (13).…”

Drosophila Rab2 controls endosome-lysosome fusion and LAMP delivery to late endosomes

“…pm-Cherry-GFP-Atg8a was a gift from Dr. Tor Erik Rusten (University of Oslo, Oslo, Norway). c929-Gal4 [93] was kindly provided by Dr. Paul Taghert (Washington University, St. Louis).…”

Functional Dissection of a Neuronal Network Required for Cuticle Tanning and Wing Expansion inDrosophila

“…To define the role(s) of N CCAP in bursicon release and to better understand the molecular and cellular determinants of tanning and wing expansion in Drosophila, we have characterized the adult distribution of bursicon and shown that the hormone localizes to a subset of N CCAP primarily included in the expression pattern of the enhancer-trap line c929-Gal4 (Hewes et al, 2003). We have compared the physiological effects of targeted manipulations of N CCAP , and of the subset of N CCAP within the c929-Gal4 pattern (N CCAP -c929), to show that N CCAP consists of two functionally distinct groups of neurons that interact to regulate release of bursicon into the hemolymph from the abdominal ganglion in a PKA-dependent manner.…”