Neurotransmitter Levels and Synaptic Strength at theDrosophilaLarval Neuromuscular Junction are not Altered by Mutation in theSluggish-aGene, Which Encodes Proline Oxidase and Affects Adult Locomotion

Abstract

The sluggish-A (slgA) gene of Drosophila melanogaster has been shown to encode for the enzyme proline oxidase, a mitochondrial enzyme which catalyzes the first step in the conversion of L-proline to L-glutamate. The slgA transcript is expressed in both larval and adult Drosophila melanogaster. Mutations in this gene lead to reduced proline oxidase activity and an elevation of free proline levels. Adult mutant flies show a striking reduction of motor activity. Since proline oxidase may contribute to the supply of the neurotransmitter glutamate in the nervous system, a reduction in proline oxidase activity could reduce neural glutamate pools and affect synaptic transmission in neurons utilizing glutamate as a transmitter, including peripheral motor neurons. We tested the hypothesis that glutamate, and synaptic transmission mediated by glutamate, are reduced at synapses of glutamatergic motor neurons in slgA mutants. Levels of glutamate and proline in different cell compartments, and functional properties of synaptic transmission were compared in slgA and control specimens. Proline is elevated in muscle cells of slgA mutants, indicating that the slgA gene regulates tissue proline levels. In nerve terminal varicosities, proline levels were low in both mutants and controls. Glutamate levels in nerve terminal varicosities of slgA mutants and controls were similar. In addition, we found that glutamatergic synaptic transmission at individual nerve endings and at the whole-cell level was similar in slgA mutants and controls. Thus, proline oxidase does not play a major role in generating neuronal glutamate pools at the Drosophila larval neuromuscular junction, and larval neuromuscular performance is not altered significantly in slgA mutants. Metabolic pathways other than that involving proline oxidase are able to sustain glutamatergic synaptic function in Drosophila larvae.

Localization of Glutamate-like Immunoreactive Neurons in the Central and Peripheral Nervous System of the Adult and Developing Pond Snail,Lymnaea stagnalis

“…However, we failed to demonstrate immunolabeling either in any of the B1-4 motoneurons or in the salivary gland itself. GLU is also the principal excitatory neurotransmitter in motoneurons of arthropods (Johansen et al, 1989;Usherwood, 1994;Shupliakov et al, 1995, Burrows, 1996Shayan et al, 2000).…”

Molecular cloning and characterization of a putative proline dehydrogenase gene in the Colorado potato beetle, Leptinotarsa decemlineata

“…Dietary ingestion of bacterially expressed LdProDH ‐dsRNA significantly decreased its mRNA level, and caused an elevation of free proline content in the hemolymph of L. decemlineata adults. Consistent with our results, mutations in this gene lead to reduced proline oxidase activity and hyperprolinemia in both D. melanogaster (Hayward et al ., ; Shayan et al ., ) and human beings (Jacquet et al ., ). Thus, our results indicated that LdProDH protein should catalyze proline catabolism in vivo .…”

“…Up to now, the putative genes encoding ProDH-like proteins have been completely or partially cloned in Drosophila melanogaster (Hayward et al, 1993) and 11 other Drosophila species (Richards et al, 2005;Clark et al, 2007;Ranz et al, 2007), Anopheles gambiae (Holt et al, 2002), Aedes aegypti (Nene et al, 2007), Culex quinquefasciatus (XM_001851357.1), Apis mellifera (XM_395275.3), Tribolium castaneum (Richards et al, 2008), Pediculus humanus corporis (DS235321.1) and Acyrthosiphon pisum (XM_001950466.1). Mutations in this gene lead to reduced proline oxidase activity and an elevation of free proline levels in D. melanogaster (Hayward et al, 1993;Shayan et al, 2000) and human beings (Jacquet et al, 2002). Moreover, D. melanogaster mutant adults greatly decrease their motor activity (Shayan et al, 2000).…”

“…Mutations in this gene lead to reduced proline oxidase activity and an elevation of free proline levels in D. melanogaster (Hayward et al, 1993;Shayan et al, 2000) and human beings (Jacquet et al, 2002). Moreover, D. melanogaster mutant adults greatly decrease their motor activity (Shayan et al, 2000).…”