Adar is expressed in the developing nervous system, making it a candidate for the editase that acts on para voltage-gated Na+ channel transcripts in the central nervous system. Surprisingly, Adar itself undergoes developmentally regulated RNA editing that changes a conserved residue in the catalytic domain. These findings show that both transcription and processing of Adar transcripts are under strict developmental control and suggest that the process of RNA editing in Drosophila is dynamically regulated (Palladino. 2000a).
A search for available mutations near the Adar locus revealed no breakpoints or useful transposon insertions. Insertions in the Adar locus, on the X chromosome, were obtained through site-selected P element mutagenesis. In a screen of 20,000 lines, three insertions into the 5' regulatory region of the Adar gene, near the two predicted promoters of Adar, were generated. Molecular analysis reveals that all 13 mutations harbor deletions of the Adar locus and comprise several classes. One class deletes DNA unidirectionally in the 5' direction removing exon -4a and upstream 5' regulatory regions (alleles 2B3 and 5A1). Another, the largest class, consists of bi-directional deletions that remove all of exons -4a and -4b and the predicted promoter regions (alleles 1F1, 1F4, 1G3, 2J3, 4A1, 4F1, 5I2, 6A2, and 6K1). Lastly, two deletions were recovered that are unidirectional in the 3' direction; allele 6C1 deletes from the P element insertion site to a region between alternative exons -1 and 0, and allele 5G1 completely deletes the Adar locus including all coding sequences (Palladino, 2000b).
All of the Adar mutants obtained from the P-element screen are conditionally lethal. That is, under ideal growth conditions Adar mutants developed into morphologically normal adults that display profound behavioral deficits and these phenotypes are recessive. All Adar alleles are phenotypically indistinguishable, including the 5G1 allele that deletes the entire Adar locus (Palladino, 2000b).
One behavioral defect observed in Adar mutant males is an extreme defect in mating. Adar- males rarely successfully mate with wild-type (WT) females. Nevertheless, a rare successful mating between females heterozygous for Adar2B3 and Adar2B3 males was able to produce viable progeny amongst which were females homozygous for Adar2B3. Mutant females display behavioral defects similar to hemizygous males. Females homozygous for all alleles of Adar display mutant behavioral phenotypes similar to hemizygous Adar- males. In contrast, homozygous Adar- females can be mated by WT males, are fertile, and give rise to morphologically normal Adar- male progeny, which exhibit the Adar- adult behavioral defects. Since Adar- male progeny of mothers lacking Adar are indistinguishable from those generated by mothers heterozygous for Adar-, it is concluded that there is no significant requirement for a maternal contribution of Adar activity. Thus, Adar would seem not to be required during early development (Palladino, 2000b).
Since it has been shown that maternal Adar is dispensable, it was of interest to determine whether Adar- animals display normal development in the absence of a zygotic contribution of Adar. The time course of development from egg-laying to pupariation of WT and Adar1F1 was examined. No significant difference was observed. As well, no significant difference between WT and mutant animals in the time course from onset of pupariation to eclosion into morphologically normal adults was observed. Adar mutant animals show a slight reduction in viability versus WT (Palladino, 2000b).
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date revised: 20 November 2006
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