On the role of normal acetylcholine metabolism in the formation and maintenance of the Drosophila nervous system

Alteration in cellular acetylcholine influences dauer formation in Caenorhabditis elegans

Altered acetylcholine (Ach) homeostasis is associated with loss of viability in flies, developmental defects in mice, and cognitive deficits in human. Here, we assessed the importance of Ach in Caenorhabditis elegans development, focusing on the role of Ach during dauer formation. We found that dauer formation was disturbed in choline acetyltransferase (cha-1) and acetylcholinesterase (ace) mutants defective in Ach biosynthesis and degradation, respectively. When examined the potential role of G-proteins in dauer formation, goa-1 and egl-30 mutant worms, expressing mutated versions of mammalian G_o and G_q homolog, respectively, showed some abnormalities in dauer formation. Using quantitative mass spectrometry, we also found that dauer larvae had lower Ach content than did reproductively grown larvae. In addition, a proteomic analysis of acetylcholinesterase mutant worms, which have excessive levels of Ach, showed differential expression of metabolic genes. Collectively, these results indicate that alterations in Ach release may influence dauer formation in C. elegans. [BMB Reports 2014; 47(2): 80-85]

Nonvesicular release of acetylcholine is required for axon targeting in the Drosophila visual system

We report evidence for a developmental role of acetylcholine in axon pathfinding in the Drosophila visual system. Acetylcholine was detected on photoreceptor axons during their navigation to target sites in the brain, a time well before the formation of functional synapses. The pattern of photoreceptor axon projections was severely disrupted when acetylcholine synthesis or metabolism was altered or eliminated, or when transgenic alpha-bungarotoxin, a nicotinic acetylcholine receptor antagonist, was expressed in the developing eye or brain. The requirement for acetylcholine signaling exists before photoreceptor neurons form synaptic connections and does not require the function of vesicular acetylcholine transporter protein. That this early effect of acetylcholine is mediated through nonvesicular release is further supported by the observation that transgenic expression of tetanus toxin, a blocker of neurotransmitter release via synaptic vesicles, did not cause similar photoreceptor axon projection defects. These observations support the notion that a form of acetylcholine secretion mediates the behavior of growth cones during axon pathfinding.

Altered electrical properties in Drosophila neurons developing without synaptic transmission

We examine the role of synaptic activity in the development of identified Drosophila embryonic motorneurons. Synaptic activity was blocked by both pan-neuronal expression of tetanus toxin light chain (TeTxLC) and by reduction of acetylcholine (ACh) using a temperature-sensitive allele of choline acetyltransferase (Cha(ts2)). In the absence of synaptic activity, aCC and RP2 motorneurons develop with an apparently normal morphology and retain their capacity to form synapses. However, blockade of synaptic transmission results in significant changes in the electrical phenotype of these neurons. Specifically, increases are seen in both voltage-gated inward Na(+) and voltage-gated outward K(+) currents. Voltage-gated Ca(2+) currents do not change. The changes in conductances appear to promote neuron excitability. In the absence of synaptic activity, the number of action potentials fired by a depolarizing ramp (-60 to +60 mV) is increased and, in addition, the amplitude of the initial action potential fired is also significantly larger. Silencing synaptic input to just aCC, without affecting inputs to other neurons, demonstrates that the capability to respond to changing levels of synaptic excitation is intrinsic to these neurons. The alteration to electrical properties are not permanent, being reversed by restoration of normal synaptic function. Whereas our data suggest that synaptic activity makes little or no contribution to the initial formation of embryonic neural circuits, the electrical development of neurons that constitute these circuits seems to depend on a process that requires synaptic activity.

Metamorphosis of tangential visual system neurons in Drosophila

To learn about construction of the adult nervous system, we studied the differentiation of imaginal neurons in the Drosophila visual system. OL2-A and OL3 are tangential neurons that display dFMRFa neuropeptide gene expression in adults but not in larvae. The two large OL2-A neurons are generated near the end of the embryonic period and already show morphological differentiation at the start of metamorphosis. The numerous small OL3 neurons are generated postembryonically and first detected later in metamorphosis. The onset of dFMRFa transcription coincides with that of neuropeptide accumulation in OL2-A neurons, but it precedes peptide accumulation in the OL3 neurons by days. Altering each of the five conserved sequences within the minimal 256-bp OL dFMRFa enhancer affected in vivo OL transcriptional activity in two cases: alteration of a TAAT element greatly diminished and alteration of a 9-bp tandem repeat completely abolished OL2-A/OL3 reporter activity. A 46-bp concatamer containing the TAAT element, tested separately, was not active in OL neurons. We propose a model of neuronal differentiation at metamorphosis that features developmental differences between classes of imaginal neurons.

Localization of choline acetyltransferase-expressing neurons in Drosophila nervous system

A variety of approaches have been developed to localize neurons and neural elements in nervous system tissues that make and use acetylcholine (ACh) as a neurotransmitter. Choline acetyltransferase (ChAT) is the enzyme catalyzing the biosynthesis of ACh and is considered to be an excellent phenotypic marker for cholinergic neurons. We have surveyed the distribution of choline acetyltransferase (ChAT)-expressing neurons in the Drosophila nervous system detected by three different but complementary techniques. Immunocytochemistry, using anti-ChAT monoclonal antibodies results in identification of neuronal processes and a few types of cell somata that contain ChAT protein. In situ hybridization using cRNA probes to ChAT messenger RNA results in identification of cell bodies transcribing the ChAT gene. X-gal staining and/or beta-galactosidase immunocytochemistry of transformed animals carrying a fusion gene composed of the regulatory DNA from the ChAT gene controlling expression of a lacZ reporter has also been useful in identifying cholinergic neurons and neural elements. The combination of these three techniques has revealed that cholinergic neurons are widespread in both the peripheral and central nervous system of this model genetic organism at all but the earliest developmental stages. Expression of ChAT is detected in a variety of peripheral sensory neurons, and in the brain neurons associated with the visual and olfactory system, as well as in neurons with unknown functions in the cortices of brain and ganglia.

Transmitter-induced calcium signalling in cultured neurons of the insect brain

The insect brain offers a unique opportunity for cell biological investigation of calcium signalling in relatively homogeneous neuronal populations, such as the mushroom body neurons. This review summarizes fluorescence imaging experiments with the indicator dye fluo-3 to investigate the calcium responses to transmitter stimulation of honeybee mushroom body neurons in primary culture. Application of acetylcholine (ACh) or nicotine promoted a calcium influx into the cell body and neurites. The increase in intracellular calcium after ACh stimulation was blocked by alpha-bungarotoxin. These results support previous histochemical studies that suggested the expression of nicotinic cholinergic receptors on Kenyon cells. An increase in cytoplasmic calcium levels leads in specific neurons to the generation of nitric oxide (NO) by a Ca2+/calmodulin activated NO synthase. NO is thought to diffuse as a short-lived messenger molecule through the plasma membrane. Using a sensitive photometric assay it could be shown that dissociated cells from the locust brain release NO after stimulation by agents elevating cytoplasmic Ca2+ levels and by the excitatory neurotransmitter ACh. The experiments in dissociated culture therefore allow the demonstration of a Ca(2+)-dependent release during nerve cell depolarization, which is a basic requirement for identifying NO as a messenger molecule.

Replacement of the glycoinositol phospholipid anchor of Drosophila acetylcholinesterase with a transmembrane domain does not alter sorting in neurons and epithelia but results in behavioral defects

Drosophila has a single glycoinositol phospholipid (GPI)-anchored form of acetylcholinesterase (AChE) encoded by the Ace locus. To assess the role that GPI plays in the physiology, of AChE, we have replaced the wild-type GPI-AChE with a chimeric transmembrane form (TM-AChE) in the nervous system of the fly. Ace null alleles provided a genetic background completely lacking in endogenous GPI-AChE, and Ace minigene P transposon constructs were used to express both GPI- and TM-AChE forms in the tissues where AChE is normally expressed. Control experiments with the GPI-AChE minigene demonstrated a threshold between 9 and 12% of normal AChE activity for adult viability. Ace mutant flies were rescued by GPI-AChE minigene lines that expressed 12-40% of normal activity and were essentially unchanged from wild-type flies in behavior. TM-AChE minigene lines were able to rescue Ace null alleles, although with a slightly higher threshold than that for GPI-AChE. Although rescued flies expressing GPI-AChE at a level of 12% of normal activity were viable, flies expressing 13-16% of normal activity from the TM-AChE transgene died shortly after eclosion. Flies expressing TM-AChE at about 30% of normal levels were essentially unchanged from wild-type flies in gross behavior but had a reduced lifespan secondary to subtle coordination defects. These flies also showed reduced locomotor activity and performed poorly in a grooming assay. However, light level and electron microscopic immunocytochemistry showed no differences in the localization of GPI- and TM-AChE. Furthermore, endogenous and ectopic-induced expression of both AChEs in epithelial tissues of the adult and embryo, respectively, showed that they were sorted identically. Most epithelial cells sorted GPI- and TM-AChE to the apical surface, but cuticle-secreting epithelia sorted both proteins basolaterally. Our data suggest that rather than having a primary role in protein sorting, the GPI anchor or AChE plays some other more subtle cellular role in neuronal physiology.

Regulation of choline acetyltransferase/lacZ fusion gene expression in putative cholinergic neurons of Drosophila melanogaster

We have analyzed the distribution of putative cholinergic neurons in whole-mount preparations of adult Drosophila melanogaster. Putative cholinergic neurons were visualized by X-gal staining of P-element transformed flies carrying a fusion gene consisting of 5' flanking DNA from the choline acetyltransferase (ChAT) gene and lacZ reporter gene. We have previously demonstrated that cryostat sections of transgenic flies carrying 7.4 kb of ChAT 5' flanking DNA show reporter gene expression in a pattern essentially similar to the known distribution of ChAT protein. Whole-mount staining of these same flies by X-gal should thus represent the overall distribution of ChAT-positive neurons. Extensive staining was observed in the cephalic, thoracic, and stomodeal ganglia, primary sensory neurons in antenna, maxillary palps, labial palps, leg, wing, and male genitalia. Primary sensory neurons associated with photoreceptors and tactile receptors were not stained. We also examined the effects of partial deletions of the 7.4 kb fragment on reporter gene expression. Deletion of the 7.4 kb fragment to 1.2 kb resulted in a dramatic reduction of X-gal staining in the peripheral nervous system (PNS). This indicates that important regulatory elements for ChAT expression in the PNS exist in the distal region of the 7.4 kb fragment. The distal parts of the 7.4 kb fragment, when fused to a basal heterologous promoter, can independently confer gene expression in subsets of putative cholinergic neurons. With these constructs, however, strong ectopic expression was also observed in several non-neuronal tissues.

Expression of the acetylcholinesterase transcript in the chordotonal neurons of Drosophila embryos

The transcript of the acetylcholinesterase gene (Ace) was detected in the central nervous system (CNS) and the lateral chordotonal neurons (lch3, lch5) of wild type Drosophila melanogaster embryos. Ace126, a representative mutation of the acetylcholinesterase gene, abolished expression in the lch3 and lch5 neurons and slightly reduced the number of lch5 cells in some abdominal segments. The number of lch5 neurons was also reduced in Ace hemizygous and transheterozygous mutant embryos. The correlation between the lack of Ace expression and the mild defect of lateral chordotonal neurons is discussed.

Expression of the ligand-binding nicotinic acetylcholine receptor subunit D alpha 2 in the Drosophila central nervous system

The D alpha 2 gene encodes a ligand-binding subunit of nicotinic acetylcholine receptors (nAChRs) from Drosophila melanogaster. We have studied the distribution of D alpha 2 transcripts and protein by in situ hybridization and immunohistochemistry, respectively, as well as the regulation of D alpha 2 gene expression in vivo using D alpha 2 promoter fragments fused to the Escherichia coli lacZ gene. Transcripts and protein from the D alpha 2 gene were detected exclusively in the central nervous system. Both in late embryos and adults D alpha 2-like immunoreactivity is widely but not uniformly distributed in the synaptic neuropil, suggesting that the D alpha 2 protein is a subunit of a synaptic nicotinic receptor. Its distribution resembles that of ALS and ARD proteins, two other nAChR subunits of the fly. Five different D alpha 2-lacZ fusion gene constructs were introduced into the Drosophila genome by P-element-mediated gene transfer to identity functional elements of the D alpha 2 promoter. All constructs produce a basic lacZ expression pattern that is compatible with the distribution of D alpha 2 transcripts and protein. A 880 bp upstream fragment harbors the cis elements for the expression of a weak but specific basic D alpha 2 pattern. The next 350 bp further upstream significantly enhance beta-galactosidase expression without influencing the pattern of expression. Between 1.7 and 7.3 kb upstream of the transcription start site one or more elements that are required for D alpha 2 expression in optic lobe tangential cells are located.

Immunohistochemical localization of a ligand-binding and a structural subunit of nicotinic acetylcholine receptors in the central nervous system of Drosophila melanogaster

The distribution of two subunits of nicotinic acetylcholine receptors in the developing and the differentiated central nervous system of Drosophila melanogaster was studied. With subunit-specific antibodies raised against the ligand-binding alpha-like subunit ALS and the putative non-ligand-binding subunit ARD, we find both ALS-like and ARD-like immunoreactivity widely distributed in most neuropiles of the optic lobes, the protocerebrum, the deutocerebrum and the thoracic ganglion of the adult fly. With a single exception, namely in the lamina of the visual system, the antigens recognized by the two types of antibodies are colocalized. This observation is consistent with previous immunoprecipitation data indicating that the ALS and ARD proteins are integral components of the same hetero-oligomeric receptor that binds the nicotinic antagonist alpha-bungarotoxin with high affinity. During embryonic development ARD-like immunoreactivity is first detectable in approximately 10 hour old embryos. Both subunits are consistently detected in the central nervous system of the late embryo, the three larval stages, and all prepupal and pupal stages. During metamorphosis the optic stalk is transiently immunoreactive with anti-ARD, but not with anti-ALS antiserum. Although in larvae and adults, immunoreactivity with both types of antibodies is most abundant in synaptic regions, in embryos and pupae strong staining of cortical cell body layers is observed, in particular with anti-ARD antisera. As these developmental periods coincide with strong accumulation of ARD transcripts, the cell body staining may reflect newly synthesized and assembled receptors, while the functional ARD- and ALS-containing receptor may be destined for synapses.

Developmental regulatory elements in the 5' flanking DNA of the Drosophila choline acetyltransferase gene

Choline acetyltransferase (ChAT, EC 2.3.1.6) catalyzes the production of the neurotransmitter acetylcholine, and is an essential factor for neurons to be cholinergic. We have analyzed regulation of the Drosophila ChAT gene during development by examining the β-galactosidase expression pattern in transformed lines carrying different lengths of 5' flanking DNA fused to a lacZ reporter gene. The largest fragment tested, 7.4 kb, resulted in the most extensive expression pattern in embryonic and larval nervous system and likely reflects all the cis-regulatory elements necessary for ChAT expression. We also found that 5' flanking DNA located between 3.3 kb and 1.2 kb is essential for the reporter gene expression in most of the segmentally arranged embryonic sensory neurons as well as other distinct cells in the CNS. The existence of negative regulatory elements was suggested by the observation that differentiating photoreceptor cells in eye imaginal discs showed the reporter gene expression in several 1.2 kb and 3.3 kb transformants but not in 7.4 kb transformants. Furthermore, we have fused the 5' flanking DNA fragments to a wild type ChAT cDNA and used these constructs to transform Drosophila with a Cha mutant background. Surprisingly, even though different amounts of 5' flanking DNA resulted in different spatial expression patterns, all of the positively expressing cDNA transformed lines were rescued from lethality. Our results suggest that developmental expression of the ChAT gene is regulated both positively and negatively by the combined action of several elements located in the 7.4 kb upstream region, and that the more distal 5' flanking DNA is not necessary for embryonic survival and development to adult flies.

Dual muscarinic and nicotinic action on a motor program in Drosophila

The effect of cholinergic agonists and antagonists on the central pattern generator of the pharyngeal muscles has been studied in third instar larvae of Drosophila. The pharyngeal muscles are a group of rhythmically active fibers involved in feeding. Bath application of the cholinergic agonists carbachol, muscarine, pilocarpine, and acetylcholine (ACh) to a semiintact preparation including the pharyngeal muscles and the central nervous system (CNS), initiated long-lasting endogenous-like bursting activity in the muscles. The muscarinic antagonists, atropine and scopolamine, blocked these responses as well as endogenous activity. Perfusion with nicotine elicited a short, tonic response that was marginally blocked by mecamylamine but not by curare, alpha-bungarotoxin, hexamethonium, or the muscarinic antagonists. This is the first time that a response to cholinergic drugs has been examined in Drosophila. The pharyngeal muscle preparation may prove to be a valuable system for studying mutations of cholinergic metabolism, receptors, and second messengers.

Initial cholinergic differentiation in embryonic chick retina is responsive to insulin and cell-cell interactions

Previous work [Kyriakis et al., Proc. Natl. Acad. Sci. U.S.A., 84 (1987) 7463-7467] had shown that insulin, when added during a window of binding from embryonic days 9-11, stimulates the normal developmental increase in choline acetyltransferase (ChAT) activity (a marker for cholinergic differentiation) in cultured embryonic chick retinal neurons. Here, we investigated the effect of insulin and IGF 1 on embryonic chick retinal neurons at the stage of development (embryonic day 6) when ChAT activity is first expressed. We investigated insulin peptide effects in retinal tissue developing in vitro as well as in cultures of retinal cells. We show that insulin also stimulated the initial embryonic increase in ChAT activity but had no stimulatory effect on glutamic acid decarboxylase activity (a marker for GABAergic differentiation), an enzyme whose activity also increases developmentally in the same retinal neurons. In fact, insulin inhibited the expression of GAD activity in the retina. The insulin-mediated increase in ChAT activity was independent of normal cell-cell interactions but could not replace them. Insulin also stimulated choline uptake but only after a two day delay, suggesting that the normal program for cholinergic differentiation in the chick retina was induced by insulin. IGF 1 did not have any effect on either cholinergic or GABAergic differentiation. We conclude that cholinergic differentiation in chick embryo retinal neurons is dependent on both insulin- and cell contact-mediated signals.

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 (greater than or equal to 70% identity), one of which encompasses a putative co-factor-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.

Sequence of choline acetyltransferase temperature-sensitive mutants determined by the polymerase chain reaction

Two temperature-sensitive alleles of Drosophila melanogaster, Cha(ts1) and Cha(ts2), have been previously identified and are thought to be point mutations in the structural gene for the neurotransmitter biosynthetic enzyme choline acetyltransferase. In order to clarify the molecular nature of these alleles and characterize the presumed amino acid substitutions, we have used the polymerase chain reaction to amplify choline acetyltransferase messenger ribonucleic acid fragments from both mutant genotypes. Amplified mutant complementary deoxyribonucleic acid was cloned and used to construct chimeric complementary deoxyribonucleic acid clones containing approximately two-thirds of the wild-type sequence which would code for N-terminal amino acids and one-third of the mutant sequence coding for the C-terminal amino acids. After in vitro translation of complementary ribonucleic acid produced from the chimeric complementary deoxyribonucleic acid clones, choline acetyltransferase activity was determined and shown to be thermolabile. Sequence analyses of these clones showed that one amino acid substitution due to single base substitution is crucial in each chimeric choline acetyltransferase complementary deoxyribonucleic acid to generate a thermolabile choline acetyltransferase product. The point mutations of the structural gene for choline acetyltransferase are thus confirmed and shown to regulate the thermolability of the enzyme produced by Cha(ts1) and Cha(ts2).

A mutation that causes muscle defects also affects catecholamine metabolism in Drosophila

Biochemical analyses, employing HPLC and electrochemical detection, have shown that the mutation adl-1, which causes muscle defects, also induces a temperature-sensitive defect in catecholamine metabolism. The pool sizes of N-acetyldopamine (NADA) and N-beta-alanyldopamine (NBAD) in mutant adults incubated at 29 degrees attain only a fraction, dependent on the length of incubation, of those in mutants incubated at 22 degrees or in controls. The differences are more striking in relevant hemizygotes. Notably, dopamine is unaffected. Concomitant examination of behavior revealed a correlation between decreases in NADA and NBAD and decreases in locomotor function. That these observations suggest a requirement for catecholamine metabolism in muscle function is discussed.

Localization of Drosophila neurons that contain choline acetyltransferase messenger RNA: an in situ hybridization study

In situ hybridization with radiolabeled complementary RNA (cRNA) probes was used to determine the location of the messenger RNA (mRNA) encoding choline acetyltransferase (ChAT) in Drosophila nervous system. Areas in the cell-rich cortical regions of the cerebrum and optic lobes hybridized with substantial concentrations of the probe. This contrasted with the cell-sparse neuropil areas where no significant concentrations of probe were observed. Although most of the cortical regions were substantially labeled, there were regions within all of the areas where labeling was sparse or nonexistent. For example in the lamina, even though the monopolar cell layer appeared to be heavily labeled, there were some neuronal profiles that were not associated with the probe. Moreover, the epithelial glia that form an arch of cell profiles subjacent to the monopolar cells were not labeled, nor were amacrine neurons in the apex of the lamina near the external optic chiasma. The highest concentration of probe (approximately 140 grains/400 microns2) was observed in the laminar monopolar cell region and the cerebral cortical rind. The next most heavily labeled region (approximately 90 grains/400 microns2) occurred over cortical cells of the medulla-lobula. In the peripheral nervous system, label over the antennal sensory neurons amounted to about 75 grains/400 microns2, and the retinular cell layer of the compound eye exhibited about 60 grains/400 microns2. The control probe did not hybridize in significant quantities in either cellular or noncellular regions. This study presents evidence that large numbers of Drosophila cortical and primary sensory neurons contain the messenger RNA necessary for the production of ChAT, the acetylcholine-synthesizing enzyme. Further, our findings provide baseline information for use in ontogenetic studies of cholinergic neurons in Drosophila, and they also provide normative data for studying the effects of mutant alleles at the Cha or Ace loci upon the transcription of ChAT messenger RNA.

Immunocytochemical study of a temperature-sensitive choline acetyltransferase mutant of Drosophila melanogaster

Using a monoclonal antibody to choline acetyltransferase (ChAT), we have identified immunoreactive synaptic terminals in the neuropil regions of the cephalic ganglion of Drosophila melanogaster. This study demonstrates the distribution of antibody-labeled structures within the optic lobe, and then investigates the immunoreactivity altered by mutation in two temperature-sensitive ChAT alleles, chats-1 and chats-2. The general structure of the optic lobe was first observed by means of the silver impregnation technique. Then the presence of ChAT immunoreactivity was determined by the application of antibody [1G4] conjugated with HRP to frozen sections, followed by the 3,3'-diamino-benzidine tetratinct layers, which correspond to the three synaptic layers of the laminarneurons, in the medulla. Also, staining appeared in four distinct layers in the lobula. In addition, weaker staining was observed in the lamina, which corresponds to the retinula cell terminals. Somal layers were not stained. In Canton-S (wild-type), the three medullar layers stain distinctly at both 19 degrees C and 30 degrees C. In chats-1 at 19 degrees C, the stain appeared in the same layers as that of Canton-S, but with somewhat lower density. In chats-2 at 19 degrees C, the density of the stain was even lower. The densities of the stain in these mutants were further decreased after exposing the flies to 30 degrees C. The decreases were dependent on the length of exposure to the higher temperature. The decrease in stain of the specimens obtained after 24 hours exposure to 30 degrees C was clearly recognizable in both chats-1 and chats-2.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of acetylcholinesterase during visual system development in Drosophila

As in other insects acetylcholine (ACh) and acetylcholinesterase (AChE) function in synaptic transmission in the central nervous system of Drosophila. Studies on flies mutant for AChE indicate that in addition to its synaptic function of inactivating acetylcholine, this neural enzyme is required for normal development of the nervous system (J.C. Hall, S.N. Alahiotis, D.A. Strumpf, and K. White, 1980, Genetics 96, 939-965; R.J. Greenspan, J.A. Finn, and J.C. Hall, 1980, J. Comp. Neurol. 189, 741-774). In order to understand what role AChE may play in neural development, it is necessary to know, in detail, where and when the enzyme appears. The use of monoclonal antibodies to localize AChE in the developing visual system of wild type Drosophila has yielded the novel observation that AChE appears in photoreceptor (retinula) cells 4-6 hr after they differentiate and 3 to 4 days before they are functional. Three days later the staining in the cell body of these cells is reduced. Because retinula cells have no functional connections at the time when AChE is first detected, AChE can not be performing its standard synaptic function. Subsequent to the reduction of AChE in the retinula cells, midway through the pupal stage, the enzyme accumulates rapidly in the neuropils of the optic lobes of the brain. Thus, there is a biphasic accumulation of AChE in the developing visual system with the enzyme initially being expressed in the retinula cells and accumulating later in the optic lobes.

Neuronal acetylcholine receptors in Drosophila: mature and immature transcripts of the ard gene in the developing central nervous system

The ARD protein is a Drosophila homolog of vertebrate nicotinic acetylcholine receptor (AChR) polypeptides. Here, an analysis of transcripts of the corresponding ard gene is presented. In situ hybridization experiments revealed ard gene expression in nervous tissue only. During development, ard transcripts are prevalent in late embryos, pupae, and newly eclosed flies. Both the spatial and the temporal pattern of ard gene expression is consistent with the ARD protein being part of a neuronal AChR that is produced in large amounts during major periods of neuronal differentiation. In situ hybridization with an intron-specific probe indicated codistribution of immature and mature ard RNAs in pupae and adult flies. In addition to the mature 3.2 kb RNA species, two large immature transcripts are found in newly eclosed flies but not in embryos, suggesting a developmentally regulated processing of ard RNA.