A splice variant of theDrosophila vesicular monoamine transporter contains a conserved trafficking domain and functions in the storage of dopamine, serotonin, and octopamine

Abstract

Vesicular monoamine transporters (VMATs) mediate the transport of dopamine (DA), serotonin (5HT), and other monoamines into secretory vesicles. The regulation of mammalian VMAT and the related vesicular acetylcholine transporter (VAChT) has been proposed to involve membrane trafficking, but the mechanisms remain unclear. To facilitate a genetic analysis of vesicular transporter function and regulation, we have cloned the Drosophila homolog of the vesicular monoamine transporter (dVMAT). We identify two mRNA splice variants (DVMAT-A and B) that differ at their C-terminus, the domain responsible for endocytosis of mammalian VMAT and VAChT. DVMAT-A contains trafficking motifs conserved in mammals but not C. elegans, and internalization assays indicate that the DVMAT-A C-terminus is involved in endocytosis. DVMAT-B contains a divergent C-terminal domain and is less efficiently internalized from the cell surface. Using in vitro transport assays, we show that DVMAT-A recognizes DA, 5HT, octopamine, tyramine, and histamine as substrates, and similar to mammalian VMAT homologs, is inhibited by the drug reserpine and the environmental toxins 2,2,4,5,6-pentachlorobiphenyl and heptachlor. We have developed a specific antiserum to DVMAT-A, and find that it localizes to dopaminergic and serotonergic neurons as well as octopaminergic, type II terminals at the neuromuscular junction. Surprisingly, DVMAT-A is co-expressed at type II terminals with the Drosophila vesicular glutamate transporter. Our data suggest that DVMAT-A functions as a vesicular transporter for DA, 5HT, and octopamine in vivo, and will provide a powerful invertebrate model for the study of transporter trafficking and regulation.

Fungal-derived semiochemical 1-octen-3-ol disrupts dopamine packaging and causes neurodegeneration

“…Indeed, we previously found that an increase in reactive oxygen species is observed in head extracts from 1-octen-3-ol-exposed flies (16). Previous studies modeling Parkinson disease in Drosophila demonstrated that overexpression of the vesicular monoamine transporter promotes packaging of dopamine into vesicles, thereby lowering its cytoplasmic concentrations (19,39). Human genetic studies have found that single nucleotide polymorphisms (SNPs) within the promoter region of VMAT2, in particular gain-of-function haplotypes, are also associated with decreased risk of PD in women (40).…”

“…Drosophila DAT and VMAT share high sequence similarity with mammalian DAT and VMAT2 (19,47). The dVMAT gene has two splice variants, dVMAT-A and -B; dVMAT-A is expressed in all dopaminergic, serotonergic, and octopaminergic neurons in Drosophila (19, 20).…”

“…The Drosophila VMAT gene contains two splice variants, dVMAT-A and -B, where dVMAT-A is expressed in all dopaminergic, serotonergic, and octopaminergic neurons and functions similarly to mammalian VMAT2 (19,20). To assess the potential for 1-octen-3-ol to exert dopaminergic toxicity through disruption of dopamine handling in vivo, we first exposed two loss-of-function mutant lines for dVMAT-A, l(2)SH0459/+ and Delta14/+, to 0.5 ppm of 1-octen-3-ol (21).…”

Dispensable, Redundant, Complementary, and Cooperative Roles of Dopamine, Octopamine, and Serotonin inDrosophila melanogaster

“…To explore the function and interaction of aminergic systems in Drosophila, we have taken advantage of the requirement for the vesicular monoamine transporter (VMAT) in the vesicular storage and exocytotic release of all biogenic amines within independent subsets of aminergic neurons (Liu and Edwards 1997;Duerr et al 1999;Greer et al 2005). We have previously shown that flies express a single VMAT gene (dVMAT) in 5-HT, DA, and OA neurons and that mutation of dVMAT causes multiple behavioral deficits (Simon et al 2009).…”

Big Lessons from Tiny Flies:<em> Drosophila Melanogaster </em>as a Model to Explore Dysfunction of Dopaminergic and Serotonergic Neurotransmitter Systems

“…Drosophila has only one vesicular monoamine transporter (dVMAT) gene, which produces two splice variants with distinct C-termini, dVMAT-A and dVMAT-B [34]: dVMAT-A is expressed in dopaminergic, octopaminergic and serotonergic neurons [34]. In contrast, dVMAT-B is present in a small population of optic glia and plays role in histamine homeostasis [35].…”