Involvement of the drosophila taurine/aspartate transporter dEAAT2 in selective olfactory and gustatory perceptions

Abstract

Excitatory amino acid transporters (EAATs) are membrane proteins involved in the uptake of neurotransmitter amino acids in the nervous system. The Drosophila dEAAT2 gene was previously described to encode a taurine/aspartate transporter. To analyze further the expression pattern and physiological function of this protein, we generated transgenic flies containing either the dEAAT2 promoter region fused to GAL4 (dEAAT2-GAL4) or a transgene allowing expression of a dEAAT2::GFP fusion protein (UAS-dEAAT2::GFP). We observed that dEAAT2-GAL4 expresses green fluorescent protein (GFP) in neurons in central and peripheral structures of third-instar larvae and adult flies. Labeled neurons were found in olfactory and gustatory pathways, in which dEAAT2::GFP was detected from the dendrites of the sensory neurons up to the first- and second-order centers. dEAAT2-GAL4 is also expressed in mechanosensory neurons. We found that a viable piggyBac insertion strain disrupts dEAAT2 expression. This mutant appears morphologically normal and presents no locomotor or phototaxis impairments; however, its brain taurine level is significantly reduced compared with that of wild-type flies. The dEAAT2 mutant showed decreased avoidance behavior in the presence of high concentration of propionic acid compared with wild-type flies, but no modification of the avoidance response to benzaldehyde. In gustatory tests, both mutant and control flies were normally attracted to sucrose; however, the dEAAT2 mutant presented a higher salt sensitivity, being repulsed by low and high salt concentrations. Therefore, we conclude that dEAAT2 does function as a taurine transporter in vivo and that this protein is physiologically required for the sensory perception of specific environmental molecules.

Drosophila astrocytes cover specific territories of CNS neuropil and are instructed to differentiate by Prospero, a key effector of Notch

“…Also, mRNAs for Eaat1, the only Drosophila glutamate transporter (Besson et al, 2000), and Eaat2, a transporter for taurine and aspartate (Besson et al, 2005(Besson et al, , 2011(Besson et al, , 2000, were shown to be expressed in discrete subsets of glia in the embryonic CNS (Freeman et al, 2003; Soustelle et al, 2002;Stacey et al, 2010). We raised antisera to Eaat1 and Eaat2, and found that the Eaat1 antibody strongly labeled astrocytic membranes (Fig.…”

Drosophila melanogaster as a genetic model system to study neurotransmitter transporters

“…Despite the similarity between dEAAT1 and dEAAT2, the latter may not function as a high affinity glutamate transporter (Besson et al, 2000; Besson et al, 2005; Besson et al, 2011). Similar to other EAAT orthologs, dEAAT2 transports aspartate, but its comparative affinity for glutamate is relatively low (Besson et al, 2000).…”

“…Similar to other EAAT orthologs, dEAAT2 transports aspartate, but its comparative affinity for glutamate is relatively low (Besson et al, 2000). Surprisingly, EAAT2 also transports taurine (aminoethane sulfonic acid), a β-amino acid whose physiological role in all species remains poorly understood (Besson et al, 2005; Besson et al, 2011). Some structures in the insect brain such as the MBs are labeled by antisera to taurine (Bicker, 1991; Strausfeld et al, 2003) and a role for taurine as a neurotransmitter has been suggested, but this remains incompletely defined (Wu and Prentice, 2010).…”

“…Rather, taurine may function primarily as an osmolyte in the CNS and other tissue (Chesney et al, 2010; Schaffer et al, 2010). In mammals, taurine uptake is mediated by a distinct taurine transporter (Pramod et al, 2013), which appears to be absent in the fly and other insects (Besson et al, 2011). Consistent with an in vivo role for dEAAT2 in taurine uptake, mutations of dEAAT2 exhibit dramatically decreased tissue content of taurine (Besson et al, 2011).…”

“…In mammals, taurine uptake is mediated by a distinct taurine transporter (Pramod et al, 2013), which appears to be absent in the fly and other insects (Besson et al, 2011). Consistent with an in vivo role for dEAAT2 in taurine uptake, mutations of dEAAT2 exhibit dramatically decreased tissue content of taurine (Besson et al, 2011). The mutants also showed mild defects in the behavioral response to saline and propionic acid, but phototaxis and locomotion were similar to wild type controls; levels of aspartate and glutamate were also similar to controls (Besson et al, 2011).…”