Drosophila Vesicular Monoamine Transporter Mutants Can Adapt to Reduced or Eliminated Vesicular Stores of Dopamine and Serotonin

Abstract

Physiologic and pathogenic changes in amine release induce dramatic behavioral changes, but the underlying cellular mechanisms remain unclear. To investigate these adaptive processes, we have characterized mutations in the Drosophila vesicular monoamine transporter (dVMAT), which is required for the vesicular storage of dopamine, serotonin, and octopamine. dVMAT mutant larvae show reduced locomotion and decreased electrical activity in motoneurons innervating the neuromuscular junction (NMJ) implicating central amines in the regulation of these activities. A parallel increase in evoked glutamate release by the motoneuron is consistent with a homeostatic adaptation at the NMJ. Despite the importance of aminergic signaling for regulating locomotion and other behaviors, adult dVMAT homozygous null mutants survive under conditions of low population density, thus allowing a phenotypic characterization of adult behavior. Homozygous mutant females are sterile and show defects in both egg retention and development; males also show reduced fertility. Homozygotes show an increased attraction to light but are mildly impaired in geotaxis and escape behaviors. In contrast, heterozygous mutants show an exaggerated escape response. Both hetero-and homozygous mutants demonstrate an altered behavioral response to cocaine. dVMAT mutants define potentially adaptive responses to reduced or eliminated aminergic signaling and will be useful to identify the underlying molecular mechanisms.A MINERGIC signaling pathways regulate a variety of complex behaviors in both the fly and mammals. In Drosophila melanogaster, dopamine is thought to regulate arousal (van Swinderen et al.

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

“…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). The survival span was significantly reduced to 8 and 10 d in l(2)SH0459/+ and Delta14/+ dVMAT mutants, respectively, compared with 17 d for w 1118 wild-type flies (Fig.…”

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

“…For all other experiments WT controls were Canton-S (CS). The dVMAT null, homozygous for the loss-of-function allele (dVMAT P1 ), and the UAS-DVMAT transgene have been previously described (Oh et al 2003;Chang et al 2006;Romero-Calderon et al 2008;Simon et al 2009). Note that the UAS-DVMAT transgene used here encodes the neuronal isoform of DVMAT (DVMAT-A); a distinct RNA splice variant of dVMAT (DVMAT-B) is expressed only in a small subset of glia in the visual system and is unlikely to be relevant to the behaviors discussed here (Greer et al 2005;Romero-Calderon et al 2008).…”

“…Negative geotaxis assays were performed as described in Simon et al (2009). Briefly, 2-to 5-day-old males and females were cold anesthetized and allowed to recover for 1 day prior to testing.…”

“…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). The requirement of DVMAT for normal exocytotic transmitter release in all central aminergic neurons-rather than a single subset-presents a unique opportunity for ablating normal synaptic transmission in all aminergic systems simultaneously and then adding back each one in isolation or in combination.…”

“…Conversely, our approach allows us to determine whether a single system is sufficient to drive a particular behavior, since we start from a baseline of no exocytotic release in any aminergic system and then add back individual amines. Third, unlike some other probes of aminergic processes (Neckameyer and Quinn 1989), dVMAT is not expressed in nonneuronal tissues such as those required for cuticle hardening and pigmentation (Simon et al 2009). This restricted pattern of expression renders DVMAT particularly useful for studying neuronal processes in the absence of potentially confounding nonneuronal effects (Colas et al 1999;True 2003;Hsouna et al 2007).…”