RESUMEN
During Drosophila aversive olfactory conditioning, aversive shock information needs to be transmitted to the mushroom bodies (MBs) to associate with odor information. We report that aversive information is transmitted by ensheathing glia (EG) that surround the MBs. Shock induces vesicular exocytosis of glutamate from EG. Blocking exocytosis impairs aversive learning, whereas activation of EG can replace aversive stimuli during conditioning. Glutamate released from EG binds to N-methyl-d-aspartate receptors in the MBs, but because of Mg2+ block, Ca2+ influx occurs only when flies are simultaneously exposed to an odor. Vesicular exocytosis from EG also induces shock-associated dopamine release, which plays a role in preventing formation of inappropriate associations. These results demonstrate that vesicular glutamate released from EG transmits negative valence information required for associative learning.
Asunto(s)
Reacción de Prevención , Condicionamiento Psicológico , Drosophila melanogaster , Neuroglía , Olfato , Animales , Reacción de Prevención/fisiología , Condicionamiento Psicológico/fisiología , Drosophila melanogaster/fisiología , Glutamatos , Cuerpos Pedunculados/fisiología , Neuroglía/fisiología , Odorantes , Olfato/fisiologíaRESUMEN
Survival in many animals requires the ability to associate certain cues with danger and others with safety. In a Drosophila melanogaster aversive olfactory conditioning paradigm, flies are exposed to two odours, one presented coincidentally with electrical shocks, and a second presented 45 s after shock cessation. When flies are later given a choice between these two odours, they avoid the shock-paired odour and prefer the unpaired odour. While many studies have examined how flies learn to avoid the shock-paired odour through formation of odour-fear associations, here we demonstrate that conditioning also causes flies to actively approach the second odour. In contrast to fear memories, which are longer lasting and requires activity of D1-like dopamine receptors only in the mushroom bodies, approach memory is short-lasting and requires activity of D1-like dopamine receptors in projection neurons originating from the antennal lobes, primary olfactory centers. Further, while recall of fear memories requires activity of the mushroom bodies, recall of approach memories does not. Our data suggest that olfactory approach memory is formed using different mechanisms in different brain locations compared to aversive and appetitive olfactory memories.
Asunto(s)
Dopamina , Drosophila , Animales , Condicionamiento Clásico/fisiología , Dopamina/fisiología , Drosophila/fisiología , Drosophila melanogaster/fisiología , Interneuronas , Cuerpos Pedunculados , Odorantes , Receptores Dopaminérgicos , Olfato/fisiologíaRESUMEN
Metabolic dysfunction is thought to contribute to the severity of psychiatric disorders; however, it has been unclear whether current highsimple sugar diets contribute to pathogenesis of these diseases. Here, we demonstrate that a high-sucrose diet during adolescence induces psychosis-related behavioral endophenotypes, including hyperactivity, poor working memory, impaired sensory gating, and disrupted interneuron function in mice deficient for glyoxalase-1 (GLO1), an enzyme involved in detoxification of sucrose metabolites. Furthermore, the high-sucrose diet induced microcapillary impairments and reduced brain glucose uptake in brains of Glo1-deficient mice. Aspirin protected against this angiopathy, enhancing brain glucose uptake and preventing abnormal behavioral phenotypes. Similar vascular damage to our model mice was found in the brains of randomly collected schizophrenia and bipolar disorder patients, suggesting that psychiatric disorders are associated with angiopathy in the brain caused by various environmental stresses, including metabolic stress.
RESUMEN
Dopaminergic neurons innervate extensive areas of the brain and release dopamine (DA) onto a wide range of target neurons. However, DA release is also precisely regulated. In Drosophila melanogaster brain explant preparations, DA is released specifically onto α3/α'3 compartments of mushroom body (MB) neurons that have been coincidentally activated by cholinergic and glutamatergic inputs. The mechanism for this precise release has been unclear. Here we found that coincidentally activated MB neurons generate carbon monoxide (CO), which functions as a retrograde signal evoking local DA release from presynaptic terminals. CO production depends on activity of heme oxygenase in postsynaptic MB neurons, and CO-evoked DA release requires Ca2+ efflux through ryanodine receptors in DA terminals. CO is only produced in MB areas receiving coincident activation, and removal of CO using scavengers blocks DA release. We propose that DA neurons use two distinct modes of transmission to produce global and local DA signaling.SIGNIFICANCE STATEMENT Dopamine (DA) is needed for various higher brain functions, including memory formation. However, DA neurons form extensive synaptic connections, while memory formation requires highly specific and localized DA release. Here we identify a mechanism through which DA release from presynaptic terminals is controlled by postsynaptic activity. Postsynaptic neurons activated by cholinergic and glutamatergic inputs generate carbon monoxide, which acts as a retrograde messenger inducing presynaptic DA release. Released DA is required for memory-associated plasticity. Our work identifies a novel mechanism that restricts DA release to the specific postsynaptic sites that require DA during memory formation.
Asunto(s)
Monóxido de Carbono/metabolismo , Dopamina/metabolismo , Neuronas Dopaminérgicas/metabolismo , Cuerpos Pedunculados/metabolismo , Terminales Presinápticos/metabolismo , Animales , Animales Modificados Genéticamente , Reacción de Prevención/fisiología , Drosophila melanogaster , Femenino , Masculino , Olfato/fisiología , Transmisión Sináptica/fisiologíaRESUMEN
In Drosophila, long-term memory (LTM) formation requires increases in glial gene expression. Klingon (Klg), a cell adhesion molecule expressed in both neurons and glia, induces expression of the glial transcription factor, Repo. However, glial signaling downstream of Repo has been unclear. Here we demonstrate that Repo increases expression of the glutamate transporter, EAAT1, and EAAT1 is required during consolidation of LTM. The expressions of Klg, Repo, and EAAT1 decrease upon aging, suggesting that age-related impairments in LTM are caused by dysfunction of the Klg-Repo-EAAT1 pathway. Supporting this idea, overexpression of Repo or EAAT1 rescues age-associated impairments in LTM. Pharmacological inhibition of glutamate activity during consolidation improves LTM in klg mutants and aged flies. Altogether, our results indicate that LTM formation requires glial-dependent inhibition of glutamate signaling during memory consolidation, and aging disrupts this process by inhibiting the Klg-Repo-EAAT1 pathway.
RESUMEN
In 2003, Martin Heisenberg et al. presented a model of how associative memories could be encoded and stored in the insect brain. This model was extremely influential in the Drosophila memory field, but did not incorporate several important mammalian concepts, including ideas of separate episodic and semantic types of memory and prediction error hypotheses. In addition, at that time, the concept of memory traces recurrently entering and exiting the mushroom bodies, brain areas where associative memories are formed and stored, was unknown. In this review, I present a simple updated model incorporating these ideas, which may be useful for future studies.
Asunto(s)
Drosophila/fisiología , Memoria Episódica , Modelos Neurológicos , Animales , Percepción OlfatoriaRESUMEN
Training-dependent increases in c-fos have been used to identify engram cells encoding long-term memories (LTMs). However, the interaction between transcription factors required for LTM, including CREB and c-Fos, and activating kinases such as phosphorylated ERK (pERK) in the establishment of memory engrams has been unclear. Formation of LTM of an aversive olfactory association in flies requires repeated training trials with rest intervals between trainings. Here, we find that prolonged rest interval-dependent increases in pERK induce transcriptional cycling between c-Fos and CREB in a subset of KCs in the mushroom bodies, where olfactory associations are made and stored. Preexisting CREB is required for initial c-fos induction, while c-Fos is required later to increase CREB expression. Blocking or activating c-fos-positive engram neurons inhibits memory recall or induces memory-associated behaviors. Our results suggest that c-Fos/CREB cycling defines LTM engram cells required for LTM.
Asunto(s)
Proteína de Unión a Elemento de Respuesta al AMP Cíclico/metabolismo , Drosophila melanogaster/citología , Drosophila melanogaster/fisiología , Memoria a Largo Plazo/fisiología , Proteínas Proto-Oncogénicas c-fos/metabolismo , Transcripción Genética , Animales , Activación Enzimática , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Neuronas/metabolismo , FosforilaciónRESUMEN
During olfactory associative learning in Drosophila, odors activate specific subsets of intrinsic mushroom body (MB) neurons. Coincident exposure to either rewards or punishments is thought to activate extrinsic dopaminergic neurons, which modulate synaptic connections between odor-encoding MB neurons and MB output neurons to alter behaviors. However, here we identify two classes of intrinsic MB γ neurons based on cAMP response element (CRE)-dependent expression, γCRE-p and γCRE-n, which encode aversive and appetitive valences. γCRE-p and γCRE-n neurons act antagonistically to maintain neutral valences for neutral odors. Activation or inhibition of either cell type upsets this balance, toggling odor preferences to either positive or negative values. The mushroom body output neurons, MBON-γ5ß'2a/ß'2mp and MBON-γ2α'1, mediate the actions of γCRE-p and γCRE-n neurons. Our data indicate that MB neurons encode valence information, as well as odor information, and this information is integrated through a process involving MBONs to regulate learning and memory.
Asunto(s)
Drosophila melanogaster/fisiología , Memoria/fisiología , Olfato/fisiología , Animales , Apetito , Calcio/metabolismo , AMP Cíclico/metabolismo , Cuerpos Pedunculados/inervación , Cuerpos Pedunculados/metabolismo , Neuronas/citología , Neuronas/metabolismo , Elementos de Respuesta/genéticaRESUMEN
During olfactory appetitive learning, animals associate an odor, or conditioned stimulus (CS), with an unconditioned stimulus (US), often a sugar reward. This association induces feeding behavior, a conditioned response (CR), upon subsequent exposure to the CS. In this study, we developed a model of this behavior in isolated Drosophila brains. Artificial activation of neurons expressing the Gr5a sugar-responsive gustatory receptor (Gr5a GRNs) induces feeding behavior in starved flies. Consistent with this, we find that in dissected brains, activation of Gr5a GRNs induces Ca2+ transients in motor neurons, MN11 + 12, required for ingestion. Significantly, activation of Gr5a GRNs can substitute for presentation of sugar rewards during olfactory appetitive learning. Similarly, in dissected brains, coincident stimulation of Gr5a GRNs and the antennal lobe (AL), which processes olfactory information, results in increased Ca2+ influx into MN11 + 12 cells upon subsequent AL stimulation. Importantly, olfactory appetitive associations are not formed in satiated flies. Likewise, AL-evoked Ca2+ transients in MN11 + 12 are not produced in ex vivo brains from satiated flies. Our results suggest that a starved/satiated state is maintained in dissected brains, and that this ex vivo system will be useful for identification of neural networks involved in olfactory appetitive learning.
Asunto(s)
Conducta Apetitiva/fisiología , Proteínas de Drosophila/metabolismo , Receptores de Superficie Celular/metabolismo , Animales , Condicionamiento Clásico/fisiología , Drosophila/metabolismo , Conducta Alimentaria/psicología , Neuronas/metabolismo , Odorantes , Corteza Olfatoria , Vías Olfatorias/fisiología , Recompensa , Olfato , Gusto/fisiologíaRESUMEN
Simultaneous stimulation of the antennal lobes (ALs) and the ascending fibers of the ventral nerve cord (AFV), two sensory inputs to the mushroom bodies (MBs), induces long-term enhancement (LTE) of subsequent AL-evoked MB responses. LTE induction requires activation of at least three signaling pathways to the MBs, mediated by nicotinic acetylcholine receptors (nAChRs), NMDA receptors (NRs), and D1 dopamine receptors (D1Rs). Here, we demonstrate that inputs from the AL are transmitted to the MBs through nAChRs, and inputs from the AFV are transmitted by NRs. Dopamine signaling occurs downstream of both nAChR and NR activation, and requires simultaneous stimulation of both pathways. Dopamine release requires the activity of the rutabaga adenylyl cyclase in postsynaptic MB neurons, and release is restricted to MB neurons that receive coincident stimulation. Our results indicate that postsynaptic activity can gate presynaptic dopamine release to regulate plasticity.
Asunto(s)
Adenilil Ciclasas/metabolismo , Dopamina/metabolismo , Proteínas de Drosophila/metabolismo , Drosophila/fisiología , Cuerpos Pedunculados/fisiología , Plasticidad Neuronal , Sinapsis/metabolismo , Animales , Antenas de Artrópodos/fisiologíaRESUMEN
Accumulating evidence suggests that transcriptional regulation is required for maintenance of long-term memories (LTMs). Here we characterize global transcriptional and epigenetic changes that occur during LTM storage in the Drosophila mushroom bodies (MBs), structures important for memory. Although LTM formation requires the CREB transcription factor and its coactivator, CBP, subsequent early maintenance requires CREB and a different coactivator, CRTC. Late maintenance becomes CREB independent and instead requires the transcription factor Bx. Bx expression initially depends on CREB/CRTC activity, but later becomes CREB/CRTC independent. The timing of the CREB/CRTC early maintenance phase correlates with the time window for LTM extinction and we identify different subsets of CREB/CRTC target genes that are required for memory maintenance and extinction. Furthermore, we find that prolonging CREB/CRTC-dependent transcription extends the time window for LTM extinction. Our results demonstrate the dynamic nature of stored memory and its regulation by shifting transcription systems in the MBs.
Asunto(s)
Drosophila melanogaster/genética , Regulación de la Expresión Génica , Memoria a Largo Plazo , Cuerpos Pedunculados/metabolismo , Animales , Animales Modificados Genéticamente , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/genética , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Perfilación de la Expresión Génica/métodos , Ontología de Genes , Neuronas/metabolismo , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
BACKGROUND: Reduced insulin/insulin-like growth factor signaling (IIS) is a major cause of symmetrical intrauterine growth retardation (IUGR), an impairment in cell proliferation during prenatal development that results in global growth defects and mental retardation. In Drosophila, chico encodes the only insulin receptor substrate. Similar to other animal models of IUGR, chico mutants have defects in global growth and associative learning. However, the physiological and molecular bases of learning defects caused by chico mutations, and by symmetrical IUGR, are not clear. RESULTS: In this study, we found that chico mutations impair memory-associated synaptic plasticity in the mushroom bodies (MBs), neural centers for olfactory learning. Mutations in chico reduce expression of the rutabaga-type adenylyl cyclase (rut), leading to decreased cAMP synthesis in the MBs. Expressing a rut (+) transgene in the MBs restores memory-associated plasticity and olfactory associative learning in chico mutants, without affecting growth. Thus chico mutations disrupt olfactory learning, at least in part, by reducing cAMP signaling in the MBs. CONCLUSIONS: Our results suggest that some cognitive defects associated with reduced IIS may occur, independently of developmental defects, from acute reductions in cAMP signaling.
Asunto(s)
Adenilil Ciclasas/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/crecimiento & desarrollo , Drosophila melanogaster/metabolismo , Proteínas Sustrato del Receptor de Insulina/genética , Aprendizaje , Mutación/genética , Animales , Recuento de Células , AMP Cíclico/biosíntesis , Proteínas Sustrato del Receptor de Insulina/metabolismo , Cuerpos Pedunculados/metabolismo , TransgenesRESUMEN
Long-term memory (LTM) formation requires de novo gene expression in neurons, and subsequent structural and functional modification of synapses. However, the importance of gene expression in glia during this process has not been well studied. In this report, we characterize a cell adhesion molecule, Klingon (Klg), which is required for LTM formation in Drosophila. We found that Klg localizes to the juncture between neurons and glia, and expression in both cell types is required for LTM. We further found that expression of a glial gene, repo, is reduced in klg mutants and knockdown lines. repo expression is required for LTM, and expression increases upon LTM induction. In addition, increasing repo expression in glia is sufficient to restore LTM in klg knockdown lines. These data indicate that neuronal activity enhances Klg-mediated neuron-glia interactions, causing an increase in glial expression of repo. Repo is a homeodomain transcription factor, suggesting that further downstream glial gene expression is also required for LTM.
Asunto(s)
Condicionamiento Clásico/fisiología , Proteínas de Drosophila/metabolismo , Regulación de la Expresión Génica/fisiología , Proteínas de Homeodominio/metabolismo , Memoria a Largo Plazo/fisiología , Neuroglía/metabolismo , Animales , Moléculas de Adhesión Celular/genética , Células Cultivadas , Sistema Nervioso Central/citología , Condicionamiento Clásico/efectos de los fármacos , Cicloheximida/farmacología , Drosophila , Proteínas de Drosophila/genética , Proteínas del Ojo/genética , Femenino , Antagonistas de Hormonas/farmacología , Masculino , Memoria a Largo Plazo/efectos de los fármacos , Ratones Transgénicos , Mifepristona/farmacología , Mutación/genética , Neuroglía/efectos de los fármacos , Neuronas/metabolismo , Inhibidores de la Síntesis de la Proteína/farmacología , Proteínas Proto-Oncogénicas c-myc/metabolismo , Interferencia de ARN/fisiologíaRESUMEN
Drosophila provides a powerful genetic model to analyze lipid metabolism. Drosophila has an adipose-like organ called the fat body, which plays a crucial role in energy homeostasis. Here, we conducted a fat body-specific misexpression screen to identify genes involved in lipid metabolism. We found that over-expression of a nuclear protein with nine C2 H2 type zinc-finger motifs and a PHD-finger, Misexpression suppressor of ras 4 (MESR4), reduces lipid accumulation in the fat body, whereas MESR4 knockdown increases it. We further show that MESR4 up-regulates the expression of major lipases, which may account for the reduction in lipid storage in the fat body and the release of free fatty acids (FFAs) in the body. These results suggest that MESR4 acts as an important upstream regulator of energy homeostasis.
Asunto(s)
Proteínas de Drosophila/metabolismo , Drosophila/metabolismo , Homeostasis , Lipasa/metabolismo , Metabolismo de los Lípidos , Proteínas Represoras/metabolismo , Animales , Proteínas de Drosophila/genética , Cuerpo Adiposo/metabolismo , Ácidos Grasos no Esterificados/metabolismo , Proteínas Represoras/genética , Regulación hacia ArribaRESUMEN
Several aging phenotypes, including age-related memory impairment (AMI), are thought to be caused by cumulative oxidative damage. In Drosophila, age-related impairments in 1 hr memory can be suppressed by reducing activity of protein kinase A (PKA). However, the mechanism for this effect has been unclear. Here we show that decreasing PKA suppresses AMI by reducing activity of pyruvate carboxylase (PC), a glial metabolic enzyme whose amounts increase upon aging. Increased PC activity causes AMI through a mechanism independent of oxidative damage. Instead, increased PC activity is associated with decreases in D-serine, a glia-derived neuromodulator that regulates NMDA receptor activity. D-serine feeding suppresses both AMI and memory impairment caused by glial overexpression of dPC, indicating that an oxidative stress-independent dysregulation of glial modulation of neuronal activity contributes to AMI in Drosophila.
Asunto(s)
Envejecimiento/fisiología , Proteínas de Drosophila/metabolismo , Trastornos de la Memoria/metabolismo , Memoria/fisiología , Neuroglía/metabolismo , Animales , Animales Modificados Genéticamente , Condicionamiento Clásico/fisiología , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Drosophila/metabolismo , Proteínas de Drosophila/genética , Trastornos de la Memoria/genética , Mutación , Piruvato Carboxilasa/genética , Piruvato Carboxilasa/metabolismo , Transducción de Señal/fisiologíaRESUMEN
Canonical aversive long-term memory (LTM) formation in Drosophila requires multiple spaced trainings, whereas appetitive LTM can be formed after a single training. Appetitive LTM requires fasting prior to training, which increases motivation for food intake. However, we found that fasting facilitated LTM formation in general; aversive LTM formation also occurred after single-cycle training when mild fasting was applied before training. Both fasting-dependent LTM (fLTM) and spaced training-dependent LTM (spLTM) required protein synthesis and cyclic adenosine monophosphate response element-binding protein (CREB) activity. However, spLTM required CREB activity in two neural populations--mushroom body and DAL neurons--whereas fLTM required CREB activity only in mushroom body neurons. fLTM uses the CREB coactivator CRTC, whereas spLTM uses the coactivator CBP. Thus, flies use distinct LTM machinery depending on their hunger state.
Asunto(s)
Proteínas de Drosophila/metabolismo , Drosophila/fisiología , Ayuno , Memoria a Largo Plazo , Factores de Transcripción/metabolismo , Animales , Proteína de Unión a CREB/metabolismo , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/metabolismo , Cicloheximida/farmacología , Proteínas de Drosophila/biosíntesis , Memoria a Largo Plazo/efectos de los fármacos , Cuerpos Pedunculados/fisiología , Neuronas/fisiología , Inhibidores de la Síntesis de la Proteína/farmacologíaRESUMEN
In Drosophila, the mushroom body (MB) is a critical brain structure for olfactory associative learning. During aversive conditioning, the MBs are thought to associate odour signals, conveyed by projection neurons (PNs) from the antennal lobe (AL), with shock signals conveyed through ascending fibres of the ventral nerve cord (AFV). Although synaptic transmission between AL and MB might play a crucial role for olfactory associative learning, its physiological properties have not been examined directly. Using a cultured Drosophila brain expressing a Ca(2+) indicator in the MBs, we investigated synaptic transmission and plasticity at the AL-MB synapse. Following stimulation with a glass micro-electrode, AL-induced Ca(2+) responses in the MBs were mediated through Drosophila nicotinic acetylcholine receptors (dnAChRs), while AFV-induced Ca(2+) responses were mediated through Drosophila NMDA receptors (dNRs). AL-MB synaptic transmission was enhanced more than 2 h after the simultaneous 'associative-stimulation' of AL and AFV, and such long-term enhancement (LTE) was specifically formed at the AL-MB synapses but not at the AFV-MB synapses. AL-MB LTE was not induced by intense stimulation of the AL alone, and the LTE decays within 60 min after subsequent repetitive AL stimulation. These phenotypes of associativity, input specificity and persistence of AL-MB LTE are highly reminiscent of olfactory memory. Furthermore, similar to olfactory aversive memory, AL-MB LTE formation required activation of the Drosophila D1 dopamine receptor, DopR, along with dnAChR and dNR during associative stimulations. These physiological and genetic analogies indicate that AL-MB LTE might be a relevant cellular model for olfactory memory.
Asunto(s)
Antenas de Artrópodos/fisiología , Cuerpos Pedunculados/fisiología , Transmisión Sináptica/fisiología , Animales , Conducta Animal , Encéfalo/fisiología , Calcio/fisiología , Drosophila , Estimulación Eléctrica , Femenino , Masculino , Olfato/fisiologíaRESUMEN
NMDA receptor (NMDAR) channels allow Ca(2+) influx only during correlated activation of both pre- and postsynaptic cells; a Mg(2+) block mechanism suppresses NMDAR activity when the postsynaptic cell is inactive. Although the importance of NMDARs in associative learning and long-term memory (LTM) formation has been demonstrated, the role of Mg(2+) block in these processes remains unclear. Using transgenic flies expressing NMDARs defective for Mg(2+) block, we found that Mg(2+) block mutants are defective for LTM formation but not associative learning. We demonstrate that LTM-dependent increases in expression of synaptic genes, including homer, staufen, and activin, are abolished in flies expressing Mg(2+) block defective NMDARs. Furthermore, we show that genetic and pharmacological reduction of Mg(2+) block significantly increases expression of a CREB repressor isoform. Our results suggest that Mg(2+) block of NMDARs functions to suppress basal expression of a CREB repressor, thus permitting CREB-dependent gene expression upon LTM induction.
Asunto(s)
Proteína de Unión a CREB/metabolismo , Condicionamiento Psicológico/efectos de los fármacos , Magnesio/farmacología , Neuronas/efectos de los fármacos , Receptores de N-Metil-D-Aspartato/metabolismo , Activinas/genética , Activinas/metabolismo , Análisis de Varianza , Animales , Animales Modificados Genéticamente , Proteína de Unión a CREB/genética , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , Células Cultivadas , Sistema Nervioso Central/citología , Condicionamiento Psicológico/fisiología , Relación Dosis-Respuesta a Droga , Drosophila , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Estimulación Eléctrica , Agonistas de Aminoácidos Excitadores/farmacología , Proteínas de Andamiaje Homer , Potenciación a Largo Plazo/efectos de los fármacos , Potenciación a Largo Plazo/genética , Quinasas de Proteína Quinasa Activadas por Mitógenos/genética , Quinasas de Proteína Quinasa Activadas por Mitógenos/metabolismo , Mutagénesis/fisiología , N-Metilaspartato/farmacología , Neuronas/fisiología , Nicotina/farmacología , Agonistas Nicotínicos/farmacología , Odorantes , Vías Olfatorias/efectos de los fármacos , Vías Olfatorias/fisiología , Técnicas de Placa-Clamp , Pupa , Proteínas de Unión al ARN/genética , Proteínas de Unión al ARN/metabolismo , Receptores de N-Metil-D-Aspartato/genéticaRESUMEN
CHICO, the Drosophila homolog of vertebrate insulin receptor substrate (IRS), mediates insulin/insulin-like growth factor signaling (IIS), and reductions in chico severely disrupt cell growth and proliferation. We found extensive expression of chico in various Drosophila brain regions including the mushroom bodies (MBs), critical neural structures for olfactory learning. chico null mutants have significantly reduced brain sizes and perform poorly in an olfactory associative learning task, although their sensitivity to the odors and electric shocks used in this learning paradigm are normal. When initial memory is normalized by training for different amounts of time (short-duration training protocols), memory retention and retrieval in chico flies are indistinguishable from that of wild-type flies, demonstrating that chico mutants are defective specifically for memory formation. Inducing expression of a chico(+) transgene in neurons throughout development restores normal learning in a chico background, while inducing chico(+) specifically at the adult stage does not, suggesting that chico is required for development of a brain region required for forming olfactory associations. Significantly, expressing chico(+) in the MBs restores the number of MB neurons to wild-type amounts and also rescues chico learning defects. Our results suggest that chico-dependent growth of the MBs is essential for development of learning ability.
Asunto(s)
Aprendizaje por Asociación/fisiología , Proteínas de Drosophila/genética , Proteínas Sustrato del Receptor de Insulina/genética , Péptidos y Proteínas de Señalización Intracelular/genética , Mutación/genética , Odorantes , Animales , Drosophila , Proteínas de Drosophila/biosíntesis , Proteínas Sustrato del Receptor de Insulina/biosíntesis , Péptidos y Proteínas de Señalización Intracelular/biosíntesis , Receptor de Insulina/genética , Receptor de Insulina/metabolismo , Especificidad por Sustrato/genéticaRESUMEN
Sleep is a fundamental biological process for all animals. However, the molecular mechanisms that regulate sleep are still poorly understood. Here we report that sleep-like behavior in Drosophila is severely impaired by mutations in sarah (sra), a member of the Regulator of Calcineurin (RCAN) family of genes. Sleep reduction in sra mutants is highly correlated with decreases in Sra protein levels. Pan-neural expression of sra rescues this behavioral phenotype, indicating that neuronal sra function is required for normal sleep. Since Sra regulates calcineurin (CN), we generated and examined the behavior of knock-out mutants for all Drosophila CN genes: CanA-14F, Pp2B-14D, and CanA1 (catalytic subunits), and CanB and CanB2 (regulatory subunits). While all mutants show at least minor changes in sleep, CanA-14F(KO) and CanB(KO) have striking reductions, suggesting that these are the major CN subunits regulating sleep. In addition, neuronal expression of constitutively active forms of CN catalytic subunits also significantly reduces sleep, demonstrating that both increases and decreases in CN activity inhibit sleep. sra sleep defects are suppressed by CN mutations, indicating that sra and CN affect sleep through a common mechanism. Our results demonstrate that CN and its regulation by Sra are required for normal sleep in Drosophila and identify a critical role of Ca(2+)/calmodulin-dependent signaling in sleep regulation.