Altered drug resistance and recovery from paralysis in Drosophila melanogaster with a deficient histamine-gated chloride channel

The recent identification and characterization of two genes, encoding histamine-gated chloride channel subunits from Drosophila melanogaster, has confirmed that histamine is a major neurotransmitter in the fruitfly. One of the cloned genes, hclA (synonyms: HisCl-alpha1; HisCl2), corresponds to ort (ora transientless), mutationsin which affect synaptic transmission in the Drosophila visual system. We identified a mutational change (a null mutation) in the genomic and RNA copies of hclA derived from mutants carrying the ort(1) allele. This correlates with new phenotypes observed in the mutant strain. We found hypersensitivity to the avermectin neurotoxins in both the ort(1) adult flies and third instar larvae compared to Oregon R wild-type animals. On the other hand, the mutation makes both male and female adult flies more resistant to treatment with diethyl ether, and the animals show substantially prolonged recovery from paralysis after diethylether anaesthesia, as well as from paralysis after mechanical shock, as revealed by the bang sensitivity test. Altogether, our data give direct evidence that in vivo a HCLA subunit-containing receptor has a distinct role in the neurotoxic action of the avermectins. They also provide new evidence for a function in the response to diethylether anaesthesia and, moreover, that HCLA function is not limited to the visual system.     

The rdgB gene of Drosophila: a link between vision and olfaction.

ota1 (ota = olfactory trap abnormal), an X-linked mutation of Drosophila isolated by virtue of abnormal olfactory behavior, is shown to be an allele of rdgB (retinal degeneration B), a gene required for normal visual system physiology. rdgB function is shown to be necessary for olfactory response of both adult flies and larvae, which have distinct olfactory systems. Electrophysiological recordings from the adult antenna indicate that rdgB is required for normal response in the peripheral olfactory system: some rdgB mutants show a delayed return to the resting potential following stimulation with ethyl acetate vapor. These results indicate that rdgB is required for both visual and olfactory physiology, and they suggest that visual and olfactory transduction may share at least one common molecular step in Drosophila.     

Drosophila CAKI/CMG protein, a homolog of human CASK, is essential for regulation of neurotransmitter vesicle release

Vertebrate CASK is a member of the membrane-associated guanylate kinase (MAGUK) family of proteins. CASK is present in the nervous system where it binds to neurexin, a transmembrane protein localized in the presynaptic membrane. The Drosophila homologue of CASK is CAKI or CAMGUK. CAKI is expressed in the nervous system of larvae and adult flies. In adult flies, the expression of caki is particularly evident in the visual brain regions. To elucidate the functional role of CASK, we employed a caki null mutant in the model organism Drosophila melanogaster. By means of electrophysiological methods, we analyzed, in adult flies, the spontaneous and evoked neurotransmitter release at the neuromuscular junction (NMJ) as well as the functional status of the giant fiber pathway and of the visual system. We found that in caki mutants, when synaptic activity is modified, the spontaneous neurotransmitter release of the indirect flight muscle NMJ was increased, the response of the giant fiber pathway to continuous stimulation was impaired, and electroretinographic responses to single and continuous repetitive stimuli were altered and optomotor behavior was abnormal. These results support the involvement of CAKI in neurotransmitter release and nervous system function.     

Role of oxidative stress in Drosophila aging

We review the role that oxidative damage plays in regulating the lifespan of the fruit fly, Drosophila melanogaster. Results from our laboratory show that the lifespan of Drosophila is inversely correlated to its metabolic rate. The consumption of oxygen by adult insects is related to the rate of damage induced by oxygen radicals, which are purported to be generated as by-products of respiration. Moreover, products of activated oxygen species such as hydrogen peroxide and lipofuscin are higher in animals kept under conditions of increased metabolic rate. In order to understand the in vivo relationship between oxidative damage and the production of the superoxide radical, we generated transgenic strains of Drosophila melanogaster that synthesize excess levels of enzymatically active superoxide dismutase. This was accomplished by P-element transformation of Drosophila melanogaster with the bovine cDNA for CuZn superoxide dismutase, an enzyme that catalyzes the dismutation of the superoxide radical to hydrogen peroxide and water. Adult flies that express the bovine SOD in addition to native Drosophila SOD are more resistant to oxidative stresses and have a slight but significant increase in their mean lifespan. Thus, resistance to oxidative stress and lifespan of Drosophila can be manipulated by molecular genetic intervention. In addition, we have examined the ability of adult flies to respond to various environmental stresses during senescence. Resistance to oxidative stress, such as that induced by heat shock, is drastically reduced in senescent flies. This loss of resistance is correlated with the increase in protein damage generated in old flies by thermal stress and by the insufficient protection from cellular defense systems which includes the heat shock proteins as well as the oxygen radical scavenging enzymes. Collectively, results from our laboratory demonstrate that oxidative damage plays a role in governing the lifespan of Drosophila during normal metabolism and under conditions of environmental stress.     

Fiber Number in the Mushroom Bodies of Adult Drosophila melanogaster depends on Age,Sex and Experience

The mushroom bodies are two characteristically shaped structures of the insect central brain. In Drosophila melanogaster they contain more fibers in females than in males. Within the first week of adult life the total number of fibers increases by about 15% and decreases again in flies older than 3-4 weeks. The number of mushroom body fibers is significantly reduced in flies kept under social isolation or deprived of their antennal input, but not in flies subjected to visual deprivation.     

FIBER NUMBER IN THE MUSHROOM BODIES OF ADULT DROSOPHILA MELANOGASTER DEPENDS ON AGE,SEX AND EXPERIENCE

The mushroom bodies are two characteristically shaped structures of the insect central brain. In Drosophila melanogaster they contain more fibers in females than in males. Within the first week of adult life the total number of fibers increases by about 15% and decreses again in flies older than 3–4 weeks. The number of mushroom body fibers is significantly reduced in flies kept under social isolation or deprived of their antennal input, but not in flies subjected to visual deprivation.     

Induction of epithelial tumors in Drosophila melanogaster heterozygous for the tumor suppressor gene wts

The imaginal disk cells of Drosophila have a cell cycle that is very similar to that of mammalian cells. Data concerning factors inducing tumors in these cells may directly relate to the risk of these factors for inducing cancer in humans. One of the genes involved in the regulation of cell cycle control is wts (warts), the Drosophila homolog of the mammalian tumor suppressor gene LATS1. The Drosophila wts mutations are recessive lethal. However, homozygous clones that arise in heterozygous flies in the imaginal disk cells lead to epithelial tumors, spectacular outgrowths visible on the cuticle of the adult. We have treated Drosophila larvae, heterozygous for wts, with the chemical mutagen MMS (methyl methanesulfonate) or with X-rays and measured the appearance of epithelial tumors in the eclosing adult flies. This test is a variation of the well-known Drosophila somatic mutation and recombination test (SMART), where mostly recessive markers have been used leading to visible phenotypes in the eyes and wings of the fly. We show that the sensitivity of this test is far greater than the comparable test system using the recessive eye marker white.     

Fiber number in the mushroom bodies of adult Drosophila melanogaster depends on age, sex and experience

The mushroom bodies are two characteristically shaped structures of the insect central brain. In Drosophila melanogaster they contain more fibers in females than in males. Within the first week of adult life the total number of fibers increases by about 15% and decreases again in flies older than 3-4 weeks. The number of mushroom body fibers is significantly reduced in flies kept under social isolation or deprived of their antennal input, but not in flies subjected to visual deprivation.     

Fiber number in the mushroom bodies of adult Drosophila melanogaster depends on age, sex and experience

The mushroom bodies are two characteristically shaped structures of the insect central brain. In Drosophila melanogaster they contain more fibers in females than in males. Within the first week of adult life the total number of fibers increases by about 15% and decreases again in flies older than 3-4 weeks. The number of mushroom body fibers is significantly reduced in flies kept under social isolation or deprived of their antennal input, but not in flies subjected to visual deprivation.     

Restoration of circadian behavioural rhythms in a period null Drosophila mutant (per01) by mammalian period homologues mPer1 and mPer2

BACKGROUND: Recent molecular studies suggest that mammals and Drosophila utilize similar components to generate circadian (approximately equal to 24 h) rhythms. The first identified circadian clock gene, the period (per) gene, is indispensable for behavioural rhythms in Drosophila and is represented in mammals by three orthologues, the relative roles of which are not known. In this study, we investigated the functional conservation of per by introducing the mouse mPer1 and mPer2 genes, driven by the Drosophila timeless (tim) promoter, into Drosophila melanogaster. RESULTS: Behavioural assays showed that both mPer constructs restored rhythms in per(01) flies that are otherwise arrhythmic due to a lack of endogenous per protein (PER). However, the rhythms restored by mPer2 were generally stronger and differed in periodicity from those restored by mPer1. In rhythmic transgenic flies, mPER proteins were expressed in lateral neurones and/or many cells in optic lobe. In addition, cell culture experiments indicated that the Drosophila PER partner, TIM, can form a complex with each of these two mammalian proteins. CONCLUSIONS: This study demonstrates that both mPer1 and mPer2 can function as clock components, and has implications for a functional analysis of the different per genes.     

Regulation of multimers via truncated isoforms: a novel mechanism to control nitric-oxide signaling

Nitric oxide (NO) is an essential regulator of Drosophila development and physiology. We describe a novel mode of regulation of NO synthase (NOS) function that uses endogenously produced truncated protein isoforms of Drosophila NOS (DNOS). These isoforms inhibit NOS enzymatic activity in vitro and in vivo, reflecting their ability to form complexes with the full-length DNOS protein (DNOS1). Truncated isoforms suppress the antiproliferative action of DNOS1 in the eye imaginal disc by impacting the retinoblastoma-dependent pathway, yielding hyperproliferative phenotypes in pupae and adult flies. Our results indicate that endogenous products of the dNOS locus act as dominant negative regulators of NOS activity during Drosophila development.     

Degradation of stimulus selectivity of visual cortical cells in senescent rhesus monkeys

Human visual function declines with age. Much of this decline is probably mediated by changes in the central visual pathways. We compared the stimulus selectivity of cells in primary visual cortex (striate cortex or V1) in young adult and very old macaque monkeys using single-neuron in vivo electrophysiology. Our results provide evidence for a significant degradation of orientation and direction selectivity in senescent animals. The decreased selectivity of cells in old animals was accompanied by increased responsiveness to all orientations and directions as well as an increase in spontaneous activity. The decreased selectivities and increased excitability of cells in old animals are consistent with an age-related degeneration of intracortical inhibition. The neural changes described here could underlie declines in visual function during senescence.     

A family of rhomboid-like genes: Drosophila rhomboid-1 and roughoid/rhomboid-3 cooperate to activate EGF receptor signaling

As in mammals, the Drosophila EGF receptor controls many aspects of growth and development. The rate limiting component of Drosophila Egfr signaling is Rhomboid, a seven transmembrane domain protein, whose expression prefigures Egfr signaling. Little is known about the molecular mechanism of Rhomboid function but genetic evidence suggests that it controls the activation of the ligand Spitz, a TGFalpha-like factor. Spitz/Egfr signaling regulates cell determination in the eye but here there is no apparent function for Rhomboid, an observation that casts doubt on this prevailing model of Rhomboid function. We describe our identification of six new rhomboid-like genes in Drosophila, and a large family of related genes present in organisms as diverse as bacteria and mammals; a human rhomboid homolog has also recently been described. Drosophila rhomboid-3 corresponds to the roughoid mutation; it cooperates with rhomboid-1 to control Egfr signaling in the eye, thereby solving the puzzle of the apparent lack of Rhomboid-1 function there. Rhomboid-1 and Roughoid/Rhomboid-3 act in the signal-emitting not signal-receiving cell, supporting the idea that Spitz activation is regulated by Rhomboid-like molecules.     

Exposure to hypomagnetic field space for multiple generations causes amnesia in Drosophila melanogaster

This is the introduction of Drosophila into the study of learning and memory affected by removal of the geomagnetic field (GMF) for successive generations. Using the operant visual learning/memory paradigm at a flight simulator, the present study revealed that wild-type flies raised in a hypomagnetic field environment continuously for 10 successive generations were gradually impaired in visual conditioning learning and memory formation and finally the 10th generation flies became morphs of nonlearners and completely amnesiac. The control experiments show that the impairment could not be ascribed to any apparent sensorimotor problems in Drosophila. The reverse shift from hypomagnetic field (HMF) to natural GMF restored the GMF-free induced amnesia fully after six consecutive generations. Thus, our findings demonstrate conclusively that some serious, but reversible learning and memory impairment may occur for living organisms in a prolonged separation from GMF over many consecutive generations. And Drosophila has the potential to develop into a new model organism for the study of the neurobiology of magnetism for multiple generations.     

Mechanical and temperature stressor-induced seizure-and-paralysis behaviors in Drosophila bang-sensitive mutants

"Bang-sensitive" mutants of Drosophila display characteristic repertoires of distinct seizure-and-paralysis behaviors upon mechanical shock (Ganetzky & Wu, 1982, Genetics, 100, 597-614). The authors found that each of the bang-sensitive mutants described in this paper (bas, bss, eas, and tko) also displayed similar behavioral repertoires upon exposure to either high or low temperature. These repertoires are composed of interspersed periods of seizure and paralysis, and appear to have interesting parallels with vertebrate epileptiform behavior. Analysis of gynandromorph mosaics of these bang-sensitive mutant flies indicated that anatomical foci required for these two types of behaviors do not totally overlap, as they were separable among mosaic flies. Observations on mosaic and decapitated flies demonstrated an all-or-none expression of the seizure-and-paralysis behaviors, indicating global activity and long-range interactions in the nervous system. Therefore, the diverse collection of currently available Drosophila bang-sensitive mutants may serve as a rich source for mutational and cellular analysis to identify interacting molecular networks that are responsible for seizure phenotypes.     

Genome-wide HP1 binding in Drosophila: developmental plasticity and genomic targeting signals

Heterochromatin protein 1 (HP1) is a major component of heterochromatin. It was reported to bind to a large number of genes and to many, but not all, transposable elements (TEs). The genomic signals responsible for targeting of HP1 have remained elusive. Here, we use whole-genome and computational approaches to identify genomic features that are predictive of HP1 binding in Drosophila melanogaster. We show that genes in repeat-dense regions are more likely to be bound by HP1, particularly in pericentric chromosomal regions. We also demonstrate that TEs are only bound by HP1 if they are flanked by other repeats, suggesting a cooperative mechanism of binding. Genome-wide DamID mapping of HP1 in larvae and adult flies reveals that repeat-flanked genes typically bind HP1 throughout development, whereas repeat-free genes display developmentally dynamic HP1 association. Furthermore, computational analysis shows that HP1 preferentially binds to transcribed regions of long genes. Finally, we detect low but significant amounts of HP1 along the entire X chromosome in male, but not female, flies, suggesting a link between HP1 and the dosage compensation complex. These results provide insights into the mechanisms of HP1 targeting in the natural genomic context.