Genetic, molecular and developmental analysis of the glutamine synthetase isozymes ofDrosophila melanogaster

Abstract

The glutamine synthetase isozymes of Drosophila melanogaster offer an attractive model for the study of the molecular genetics and evolution of a small gene family encoding enzymatic isoforms that evolved to assume a variety of specific and sometimes essential biological functions. In Drosophila melanogaster two GS isozymes have been described which exhibit different cellular localisation and are coded by a two-member gene family. The mitochondrial GS structural gene resides at the 21B region of the second chromosome, the structural gene for the cytosolic isoform at the 10B region of the X chromosome. cDNA clones corresponding to the two genes have been isolated and sequenced. Evolutionary analysis data are in accord with the hypothesis that the two Drosophila glutamine synthetase genes are derived from a duplication event that occurred near the time of divergence between Insecta and Vertebrata. Both isoforms catalyse all reactions catalysed by other glutamine synthetases, but the different kinetic parameters and the different cellular compartmentalisation suggest strong functional specialisation. In fact, mutations of the mitochondrial GS gene produce embryo-lethal female sterility, defining a function of the gene product essential for the early stages of embryonic development. Preliminary results show strikingly distinct spatial and temporal patterns of expression of the two isoforms at later stages of development.

Nonvesicular Release of Glutamate by Glial xCT Transporters Suppresses Glutamate Receptor ClusteringIn Vivo

“…In GOT mutants, glutamate synthesis is impaired, and NMJs show a large increase in postsynaptic glutamate receptor number (Fig. 4 B) (Chase and Kankel, 1987;Caggese et al, 1994;Featherstone et al, 2002). Thus, GOT mutants are a way of mimicking the gb mutant phenotype in a confirmed glutamate-dependent way.…”

“…(Parks et al, 2004), which completely deletes gb, as well as six more genes 5Ј to gb and eight genes 3Ј to gb. Glutamate oxaloacetate transaminase (GOT ) mutants (Featherstone et al, 2002) were got2[nj]/ SM1,got2 [1], in which enzymatic function of GOT2, the sole cytoplasmic GOT paralog in Drosophila, is eliminated (Chase and Kankel, 1987;Caggese et al, 1994). For comparison between two groups of normally distributed data, a Student's t test was used.…”

“…Semi-intact Drosophila larvae can be kept alive in culture medium for days (Ball et al, 2003), allowing relatively long-term pharmacological manipulations. GOT (Enzyme Commission 2.6.1.1) is an enzyme required for cytoplasmic glutamate synthesis in Drosophila (Chase and Kankel, 1987;Caggese et al, 1994). In GOT mutants, glutamate synthesis is impaired, and NMJs show a large increase in postsynaptic glutamate receptor number (Fig.…”

Cloning and characterization of the glutamine synthetase gene from Chinese shrimp Fenneropenaeus chinensis

“…GS of some vertebrates is not utilized in mitochondrial ammonia detoxification, so it is expressed in the cytosol and no isozyme has been detected (Caizzi et al 1990). While intramitochondrial GS converts ammonia to glutamine in insects and birds, and in these organisms a mitochondrial GS isoform exists in some tissues but a cytosolic isoform is found in other tissues (Caggese et al 1994). The molecular mechanism that underlies the tissue-specific formation of the mitochondrial and cytoplasmic isoforms may rely on either different transcription initiation sites or differential translation from the same mRNA (Laud and Campbell 1994).…”

Expression of Four Glutamine Synthetase Genes in the Early Stages of Development of Rainbow Trout (Oncorhynchus mykiss) in Relationship to Nitrogen Excretion

“…of maternal origin), as well as in several embryonic stages (23). There are two glutamine synthetase isoforms in Drosophila with some quantitative variation in the developmental pattern of expression (24). It has been estimated that transcriptional activation of the embryonic genome in rainbow trout occurs at about 3 dpf (25).…”