A cDNA clone encoding the ADP/ATP translocase of Drosophila melanogaster shows a high degree of similarity with the mammalian ADP/ATP translocases

The mitochondrial aspartate/glutamate carrier (AGC or Aralar1) isoforms in D. melanogaster: biochemical characterization, gene structure, and evolutionary analysis

BACKGROUND

In man two mitochondrial aspartate/glutamate carrier (AGC) isoforms, known as aralar and citrin, are required to accomplish several metabolic pathways. In order to fill the existing gap of knowledge in Drosophila melanogaster, we have studied aralar1 gene, orthologue of human AGC-encoding genes in this organism.

METHODS

The blastp algorithm and the "reciprocal best hit" approach have been used to identify the human orthologue of AGCs in Drosophilidae and non-Drosophilidae. Aralar1 proteins have been overexpressed in Escherichia coli and functionally reconstituted into liposomes for transport assays.

RESULTS

The transcriptional organization of aralar1 comprises six isoforms, three constitutively expressed (aralar1-RA, RD and RF), and the remaining three distributed during the development or in different tissues (aralar1-RB, RC and RE). Aralar1-PA and Aralar1-PE, representative of all isoforms, have been biochemically characterized. Recombinant Aralar1-PA and Aralar1-PE proteins share similar efficiency to exchange glutamate against aspartate, and same substrate affinities than the human isoforms. Interestingly, although Aralar1-PA and Aralar1-PE diverge only in their EF-hand 8, they greatly differ in their specific activities and substrate specificity.

CONCLUSIONS

The tight regulation of aralar1 transcripts expression and the high request of aspartate and glutamate during early embryogenesis suggest a crucial role of Aralar1 in this Drosophila developmental stage. Furthermore, biochemical characterization and calcium sensitivity have identified Aralar1-PA and Aralar1-PE as the human aralar and citrin counterparts, respectively.

GENERAL SIGNIFICANCE

The functional characterization of the fruit fly mitochondrial AGC transporter represents a crucial step toward a complete understanding of the metabolic events acting during early embryogenesis.

An EST database of the Caribbean fruit fly, Anastrepha suspensa (Diptera: Tephritidae)

Invasive tephritid fruit flies are a great threat to agriculture worldwide and warrant serious pest control measures. Molecular strategies that promote embryonic lethality in these agricultural pests are limited by the small amount of nucleotide sequence data available for tephritids. To increase the dataset for sequence mining, we generated an EST database by 454 sequencing of the caribfly, Anastrepha suspensa, a model tephritid pest. This database yielded 95,803 assembled sequences with 24% identified as independent transcripts. The percentage of caribfly sequences with hits to the closely related tephritid, Rhagoletis pomonella, transcriptome was higher (28%) than to Drosophila proteins/genes (18%) in NCBI. The database contained genes specifically expressed in embryos, genes involved in the cell death, sex-determination, and RNAi pathways, and transposable elements and microsatellites. This study significantly expands the nucleotide data available for caribflies and will be a valuable resource for gene isolation and genomic studies in tephritid insects.

Xenopus adenine nucleotide translocase mRNA exhibits specific and dynamic patterns of expression during development

We report the isolation and characterization of the Xenopus homolog to human T1 ANT (adenine nucleotide translocase). The 1290-nucleotide sequence contains initiation and termination signals, and encodes a conceptual protein of 298 amino acids. The sequence shares high amino acid identity with the mammalian adenine translocases. The transcript is present in unfertilized eggs, and it is expressed at higher levels during formation of the antero-posterior dorsal axis in embryos. Although low levels are expressed constitutively except in endodermal cells, adenine nucleotide translocase (ANT) expression is dynamically regulated during neurulation. At this stage, expression in ectoderm rapidly diminishes as the neural folds form, and then ANT expression increases slightly in mesoderm. At the culmination of neurulation, the neural tube briefly expresses ANT, and thereafter its expression predominates in the somitic mesoderm and also the chordoneural hinge. In addition, ANT expression is particularly high in the prosencephalon, the mesencephalon, the branchial arches, eye, and the otic vesicle. Treatment of embryos with retinoic acid has the effect of diminishing constitutive expression of ANT, but microinjection studies demonstrate that immediate and local repression cannot be induced in dorsal structures.Key words: adenine nucleotide translocase, Xenopus, retinoic acid, pattern formation, gastrulation.

stress sensitive B encodes an adenine nucleotide translocase in Drosophila melanogaster

Adenine nucleotide translocases (ANT) are required for the exchange of ADP and ATP across the inner mitochondrial membrane. They are essential for life, and most eukaryotes have at least two different Ant genes. Only one gene had been described from Drosophila, and this had not been characterized genetically. We show that mutations in this gene correspond to the previously described loci, sesB and l(1)9Ed. Immediately adjacent to this gene is another encoding a second ANT protein, which has 78% identity to that encoded by sesB/l(1)9Ed. These two genes are transcribed from a common promoter, and their mRNAs are produced by differential splicing. Hutter and Karch suggested that the sesB ANT gene corresponded to Hmr, a gene identified by an allele that rescues otherwise inviable interspecific hybrids between Drosophila melanogaster and its sibling species. This hypothesis is not supported by our study of the ANT genes of D. melanogaster.

Molecular analysis of a candidate gene for the reproductive isolation between sibling species of Drosophila

The X-linked gene Hmr in Drosophila melanogaster, when mutated, rescues otherwise inviable interspecific hybrids from crosses between D. melanogaster and any of its three most closely related species D. simulans, D. mauritiana and D. sechellia. DNA from the site of a breakpoint at the putative locus of the gene has been cloned, and results of transcription and sequence analyses are presented. Three distinct mRNAs are transcribed from this locus, two of which are abundantly expressed throughout life. A third transcript, which is larger but rarer, appears to be disrupted by at least one of the two known mutations of Hmr. The gene encodes a mitochondrial ADP/ATP translocator protein, which plays an essential role in maintaining metabolic energy. Analysis of several cDNAs suggested that the rescue of hybrids may be dependent on mutations in the variable 3' end region of this gene, affecting the level and/or the stability of the largest messenger RNA.

A cDNA encoding an ADP/ATP carrier from the mosquito Anopheles gambiae

Two cDNAs are described from Anopheles gambiae that correspond to the ADP/ATP carrier or translocase. The clones are identical except for minor differences in the 5' non-coding region and in the lengths of the poly-A tails. They code for mRNAs of 1261 and 1263 bp and contain one open reading frame of 906 bp. A probe made from the 1263 bp cDNA hybridized to bands of approximately 1260 and 1700 bp on developmental Northern blots. The putative 300 amino acid peptide sequence shows from 53.4-78.5% identity to AAC peptide sequences from a range of organisms from Zea mays to human. Both clones mapped to region 26a on the left arm of chromosome 2 in An. gambiae.