Structure and Organization of the DrosophilaCholinergic Locus

Abstract

The Drosophila cholinergic locus is composed of two distinct genetic functions: choline acetyltransferase (ChAT; EC 2.3.1.6), the enzyme catalyzing biosynthesis of neurotransmitter acetylcholine (ACh), and the vesicular ACh transporter (VAChT), the synaptic vesicle membrane protein which pumps transmitter into vesicles. Both genes share a common first exon and the remainder of the VAChT gene contains a single coding exon residing entirely within the first intron of ChAT. RNase protection analysis indicates that all Drosophila VAChT specific transcripts contain the shared first exon and suggests common transcriptional control for ChAT and VAChT. Similar types of genomic organization have been evolutionarily conserved for cholinergic loci in nematodes and vertebrates, and may operate to ensure coordinate expression of these functionally related genes in the same cells. The relative levels of Drosophila ChAT and VAChT mRNA differ, however, in different tissues or in Cha mutants, indicating that independent regulation of ChAT and VAChT transcripts may occur post-transcriptionally. The predicted Drosophila VAChT protein is composed of 578 amino acids and contains 12 conserved putative transmembrane domains. Full-length VAChT cDNA is 7.2 kilobase long and has unusually long 5-and 3-untranslated regions (UTR). The 5-UTR contains a GTG ChAT translational initiation codon along with three other potential ATG initiation codons. These features of the VAChT 5-UTR region suggest that a ribosome scanning model may not be used for VAChT translation initiation.

Localization of choline acetyltransferase-expressing neurons inDrosophila nervous system

“…The genes encoding subunits of the two main classes of ACh receptors, nicotinic and muscarinic, have also been identified and characterized in Drosophila (for reviews see : Gundelfinger, 1992;Gundelfinger and Hess, 1992;Hannan and Hall, 1993;Trimmer, 1995). Recently, the gene encoding Drosophila vesicular acetylcholine transporter protein has also been identified and shown to be organized along with ChAT into a cholinergic locus similar to the genomic organization seen in other species (Kitamoto et al, 1998). This wealth of genetic and molecular information on genes related to ACh metabolism has established Drosophila as an excellent model system to study the function and regulation of cholinergic neurotransmission in a comprehensive manner.…”

“…The gene for the vesicular acetylcholine transporter (VAChT) has recently been identified in Drosophila and specific antibodies have been generated (Kitamoto et al, 1998). It will be interesting in future studies to localize VAChT expression and compare its distribution to ChAT since both genes form a cholinergic locus and appear to be under common transcriptional regulation.…”

Comparative sequence analysis and tissue localization of members of the SLC6 family of transporters in adultDrosophila melanogaster

“…Alternatively, the subtle sequence differences could be significant for the timing or localization of candidate expression. This genetic region could form some sort of locus that possibly functions similarly to the cholinergic locus in Drosophila, where two sequences with different functions share the first exons (Kitamoto et al, 1998). This region could also represent an area of gene duplication, in which transporters with different substrate profiles are generated as postulated by Boudko et al (Boudko et al, 2005).…”

Eukaryotic operon-like transcription of functionally related genes in Drosophila

“…Transcripts encoding two unrelated proteins also could arise from one primary transcript by alternative splicing; an example is the Drosophila cholinergic locus (13). This mechanism predicts that the two mature mRNAs will share some 5Ј UTR sequences.…”