Drosophila GABAergic Systems: Sequence and Expression of Glutamic Acid Decarboxylase

: A mammalian glutamic acid decarboxylase (GAD) cDNA probe has been utilized to isolate Drosophila cDNA clones that represent a genomic locus in chromosome region 64A. Deletion analysis indicates that this chromosomal locus encodes an enzymatically active GAD protein. The in vitro translation of cRNA representing a Drosophila cDNA clone yields a 57‐kDa protein that can be immunoprecipitated by an anti‐GAD antiserum. A GAD‐immunoreactive protein of the same size can also be detected in Drosophila head extracts. The nucleotide sequence derived from two overlapping Drosophila cDNA clones predicts a 57,759‐dalton protein composed of 510 residues that is 53% identical to mammalian GAD. Sequence comparisons of mammalian and Drosophila GAD identify two highly conserved regions (≥70% identity), one of which encompasses a putative cofactor‐binding domain. Transcriptional analyses show that expression of the Drosophila Gad gene commences early in embryonic development (4–8 h) and continues in all later developmental stages. A 3.1‐kb class of mRNA is detected throughout embryogenesis, in all three larval stages, in pupae, and in adults. This transcript class has a widespread distribution in the adult CNS. A smaller 2.6‐kb transcript is expressed in a developmentally regulated manner; it is detected only in embryos and pupae.