Biomedical subjects

Ronald L Davis

Publications and source records attributed to Ronald L Davis.

At least 19 recordsLinked to original sources

PubMed2006

Beta 1-integrins are required for hippocampal AMPA receptor-dependent synaptic transmission, synaptic plasticity, and working memory.

Integrins comprise a large family of cell adhesion receptors that mediate diverse biological events through cell-cell and cell-extracellular matrix interactions. Recent studies have shown that several integrins are localized to synapses with suggested roles in synaptic plasticity and memory formation. We generated a postnatal forebrain and excitatory neuron-specific knock-out of beta1-integrin in the mouse. Electrophysiological studies demonstrated that these mutants have impaired synaptic transmission through AMPA receptors and diminished NMDA receptor-dependent long-term potentiation. Despite the impairment in hippocampal synaptic transmission, the mutants displayed normal hippocampal-dependent spatial and contextual memory but were impaired in a hippocampal-dependent, nonmatching-to-place working memory task. These phenotypes parallel those observed in animals carrying knock-outs of the GluR1 (glutamate receptor subunit 1) subunit of the AMPA receptor. These observations suggest a new function of beta1-integrins as regulators of synaptic glutamate receptor function and working memory.

Animals↗

PubMed2005

Drosophila DPM neurons form a delayed and branch-specific memory trace after olfactory classical conditioning.

Formation of normal olfactory memory requires the expression of the wild-type amnesiac gene in the dorsal paired medial (DPM) neurons. Imaging the activity in the processes of DPM neurons revealed that the neurons respond when the fly is stimulated with electric shock or with any odor that was tested. Pairing odor and electric-shock stimulation increases odor-evoked calcium signals and synaptic release from DPM neurons. These memory traces form in only one of the two branches of the DPM neuron process. Moreover, trace formation requires the expression of the wild-type amnesiac gene in the DPM neurons. The cellular memory traces first appear at 30 min after conditioning and persist for at least 1 hr, a time window during which DPM neuron synaptic transmission is required for normal memory. DPM neurons are therefore "odor generalists" and form a delayed, branch-specific, and amnesiac-dependent memory trace that may guide behavior after acquisition.

Animals↗

PubMed2005

A Drosophila nonvisual arrestin is required for the maintenance of olfactory sensitivity.

Nonvisual arrestins are a family of multifunctional adaptor molecules that regulate the activities of diverse families of receptors including G protein-coupled receptors, frizzled, and transforming growth factor-beta receptors. These activities indicate broad roles in both physiology and development for nonvisual arrestins. Drosophila melanogaster has a single nonvisual arrestin, kurtz, which is found at high levels within the adult olfactory receptor neurons (ORNs), suggesting a role for this gene in modulating olfactory sensitivity. Using heat-induced expression of a krz cDNA through development, we rescued krz(1) lethality. The resulting adults lacked detectable levels of krz in the olfactory system. The rescued krz(1) homozygotes have an incompletely penetrant antennal structural defect that was completely rescued by the neural expression of a krz cDNA. The krz(1) loss-of-function adults without visible antennal defects displayed diminished behavioral responsiveness to both aversive and attractive odors and also demonstrated reduced olfactory receptor potentials. Both the behavioral and electrophysiological phenotypes were rescued by the targeted expression of the krz cDNA within postdevelopmental ORNs. Thus, krz is required within the nervous system for antennal development and is required later in the ORNs for the maintenance of olfactory sensitivity in Drosophila. The reduced receptor potentials in krz(1) antenna indicate that nonvisual arrestins are required for the early odor-induced signaling events within the ORNs.

Animals↗

PubMed2005

Thirty years of olfactory learning and memory research in Drosophila melanogaster.

The last 30 years have witnessed tremendous progress in elucidating the basic mechanisms underlying a simple form of olfactory learning and memory in Drosophila. The application of the mutagenic approach to the study of olfactory learning and memory in Drosophila has yielded insights into the participation of a large number of genes in both the development of critical brain regions as well as in the physiology underlying the acquisition, storage, and retrieval of memory. Newer sophisticated molecular-genetic tools have further allowed for the specification and functional dissection of the neuronal circuitry involved in these processes at a systems level. With these advances in our understanding of the genes, neurons, and circuits involved in learning and memory, the field of Drosophila memory research is nearing a state of integration of the bottom up and top down approaches to understanding this form of behavioral plasticity.

Adaptation, Physiological↗

PubMed2005

Isolation of mRNA from specific tissues of Drosophila by mRNA tagging.

To study the function of specific cells or tissues using genomic tools like microarray analyses, it is highly desirable to obtain mRNA from a homogeneous source. However, this is particularly challenging for small organisms, like Caenorhabditis elegans and Drosophila melanogaster. We have optimized and applied a new technique, mRNA tagging, to isolate mRNA from specific tissues of D.melanogaster. A FLAG-tagged poly(A)-binding protein (PABP) is expressed in a specific tissue and mRNA from that tissue is thus tagged by the recombinant PABP and separated from mRNA in other tissues by co-immunoprecipitation with a FLAG-tag specific antibody. The fractionated mRNA is then amplified and used as probe in microarray experiments. As a test system, we employed the procedures to identify genes expressed in Drosophila photoreceptor cells. We found that most known photoreceptor cell-specific mRNAs were identified by mRNA tagging. Furthermore, at least 11 novel genes have been identified as enriched in photoreceptor cells. mRNA tagging is a powerful general method for profiling gene expression in specific tissues and for identifying tissue-specific genes.

Animals↗

PubMed2005

Remote control of fruit fly behavior.

Electrical stimulation of neurons in the central nervous system of awake, behaving animals offers the ultimate test to determine whether the activation of specific neurons is sufficient to elicit perception, motor activity, or other behaviors. In this issue of Cell, Lima and Miesenböck (Lima and Miesenböck, 2005) dump the stimulating electrode in favor of a new remote control system to excite specific neurons--light activation of transgenically supplied ion channels.

Action Potentials↗

PubMed2005

The dachshund gene is required for the proper guidance and branching of mushroom body axons in Drosophila melanogaster.

The dachshund gene encodes a transcription factor required for the proper development of Drosophila eyes, legs, and mushroom bodies. The mushroom bodies of dachshund mutants exhibit a marked reduction in the size of the vertical lobes and disorganization of the horizontal lobes. In mosaic animals, mutant axons fail to contribute significantly to the mushroom body alpha lobe. Here we show that this defect is due to the misrouting of alphabeta axons to the region normally occupied by alpha'beta' axons. This defect is pronounced for clones generated in larval stages but not clones generated after pupariation, indicating that dachshund function is particularly important around the time of puparium formation. In addition, mushroom body axons exhibit excessive branching in dachshund mutant clones. Thus, dachshund is required in mushroom body neurons for proper axon guidance and branching.

Animals↗

PubMed2005

Olfactory memory formation in Drosophila: from molecular to systems neuroscience.

The olfactory nervous system of insects and mammals exhibits many similarities, which suggests that the mechanisms for olfactory learning may be shared. Molecular genetic investigations of Drosophila learning have uncovered numerous genes whose gene products are essential for olfactory memory formation. Recent studies of the products of these genes have continued to expand the range of molecular processes known to underlie memory formation. Recent research has also broadened the neuroanatomical areas thought to mediate olfactory learning to include the antennal lobes in addition to a previously accepted and central role for the mushroom bodies. The roles for neurons extrinsic to the mushroom body neurons are becoming better defined. Finally, the genes identified to participate in Drosophila olfactory learning have conserved roles in mammalian organisms, highlighting the value of Drosophila for gene discovery.

Animals↗

PubMed2004

The role of cAMP response element-binding protein in Drosophila long-term memory.

In Drosophila, the transcription factor cAMP response element-binding protein 2 (dCREB2) has been reported to modulate the formation of long-term olfactory memory (LTM). Overexpression of a repressor isoform of CREB (dCREB2-b) under the control of a heat-shock promoter was reported to block LTM, whereas overexpression of an activator isoform (dCREB2-a) was reported to enhance LTM. A ratiometric model based on these results predicts that the balance of functional dCREB2-a and dCREB2-b provides a switch for memories to remain labile or to become enduring. We show here that the dCREB2-a transgene originally reported to enhance LTM carries a mutation that produces a translational reading-frame shift with the consequent formation of a stop codon at predicted amino acid position 79. Overexpression of this mutant dCREB2-a transgene or a corrected dCREB2-a transgene failed to show any enhancement of LTM. Overexpression of the dCREB2-b repressor transgene, in contrast, produced the anticipated block in LTM formation. We discuss the implications of these findings and propose an alternative model for the role of dCREB in Drosophila LTM.

Amino Acid Sequence↗

PubMed2004

Olfactory learning.

The olfactory nervous systems of insects and mammals exhibit many similarities, suggesting that the mechanisms for olfactory learning may be shared. Neural correlates of olfactory memory are distributed among many neurons within the olfactory nervous system. Perceptual olfactory learning may be mediated by alterations in the odorant receptive fields of second and/or third order olfactory neurons, and by increases in the coherency of activity among ensembles of second order neurons. Operant olfactory conditioning is associated with an increase in the coherent population activity of these neurons. Olfactory classical conditioning increases the odor responsiveness and synaptic activity of second and perhaps third order neurons. Operant and classical conditioning both produce an increased responsiveness to conditioned odors in neurons of the basolateral amygdala. Molecular genetic studies of olfactory learning in Drosophila have revealed numerous molecules that function within the third order olfactory neurons for normal olfactory learning.

Action Potentials↗

PubMed2004

Altered representation of the spatial code for odors after olfactory classical conditioning; memory trace formation by synaptic recruitment.

In the olfactory bulb of vertebrates or the homologous antennal lobe of insects, odor quality is represented by stereotyped patterns of neuronal activity that are reproducible within and between individuals. Using optical imaging to monitor synaptic activity in the Drosophila antennal lobe, we show here that classical conditioning rapidly alters the neural code representing the learned odor by recruiting new synapses into that code. Pairing of an odor-conditioned stimulus with an electric shock-unconditioned stimulus causes new projection neuron synapses to respond to the odor along with those normally activated prior to conditioning. Different odors recruit different groups of projection neurons into the spatial code. The change in odor representation after conditioning appears to be intrinsic to projection neurons. The rapid recruitment by conditioning of new synapses into the representation of sensory information may be a general mechanism underlying many forms of short-term memory.

Animals↗

PubMed2004

Spatiotemporal gene expression targeting with the TARGET and gene-switch systems in Drosophila.

Targeted gene expression has become a standard technique for the study of biological questions in Drosophila. Until recently, transgene expression could be targeted in the dimension of either time or space, but not both. Several new systems have recently been developed to direct transgene expression simultaneously in both time and space. We describe here two such systems that we developed in our laboratory. The first system provides a general method for temporal and regional gene expression targeting (TARGET) with the conventional GAL4-upstream activator sequence (UAS) system and a temperature-sensitive GAL80 molecule, which represses GAL4 transcriptional activity at permissive temperatures. The second system, termed Gene-Switch, is based on a GAL4-progesterone receptor chimera that is hormone-inducible. We have used both systems for simultaneous spatial and temporal rescue of memory dysfunction in the rutabaga (rut) memory mutant of Drosophila. In this protocol, we provide guidelines for the use of these two novel systems, which should have general utility in studying Drosophila biology and in using the fly as a model for human disease.

5' Flanking Region↗

PubMed2004

Gene expression systems in Drosophila: a synthesis of time and space.

Until recently, ectopic gene expression in Drosophila was largely accomplished through the use of the heat-shock promoter, which provides the experimenter with temporal control over transgene induction, or the GAL4-UAS system, which provides the experimenter with spatial control over transgene expression. But significant advances have now been made in combining the attributes of temporal and spatial control over gene expression into a single system. In this article, we review the progress on the development and implementation of several gene expression systems that offer control in time and space. These include systems employing the yeast FLP recombinase gene and FRT sites (FLP and/or FRT), tetracycline-responsive transcription factors (Tet-On and Tet-Off), steroid hormone responsive transcription factors (GeneSwitch and ER-GAL4) and temperature-sensitive repressors of the classical GAL4-UAS system (TARGET).

Animals↗

PubMed2003

Pharmacogenetic rescue in time and space of the rutabaga memory impairment by using Gene-Switch.

The GAL4-based Gene-Switch system has been engineered to regulate transgene expression in Drosophila in both time and space. We constructed a Gene-Switch transgene in which Gene-Switch expression is restricted spatially by a defined mushroom body enhancer. This system allows Gene-Switch to be active only in the mushroom bodies and only on administration of the pharmacological Gene-Switch ligand RU486. This line was used to drive the expression of a rutabaga cDNA in otherwise rutabaga mutant flies. Induction of the rutabaga cDNA in the mushroom bodies only during adulthood, or during adulthood along with the larval and pupal developmental stages, corrects the olfactory memory impairment found in rutabaga mutants. Induction of the cDNA only during the larval and pupal stages was inconsequential to performance in olfactory memory tasks. These data indicate that normal rutabaga function must be expressed in adulthood for normal memory and conclusively delimit the time and space expression requirements for correcting the rutabaga memory impairment. Such combined pharmacogenetic regulation of transgene expression now allows this time and space dissection to be made for other behavioral mutants.

Adenylyl Cyclases↗

PubMed2003

Spatiotemporal rescue of memory dysfunction in Drosophila.

We have developed a method for temporal and regional gene expression targeting (TARGET) in Drosophila and show the simultaneous spatial and temporal rescue of a memory defect. The transient expression of the rutabaga-encoded adenylyl cyclase in the mushroom bodies of the adult brain was necessary and sufficient to rescue the rutabaga memory deficit, which rules out a developmental brain defect in the etiology of this deficit and demonstrates an acute role for rutabaga in memory formation in these neurons. The TARGET system offers general utility in simultaneously addressing issues of when and where gene products are required.

Adenylyl Cyclases↗

PubMed2003

Octopamine receptor OAMB is required for ovulation in Drosophila melanogaster.

Octopamine is a major monoamine in invertebrates and affects many physiological processes ranging from energy metabolism to complex behaviors. Octopamine binds to receptors located on various cell types and activates distinct signal transduction pathways to produce these diverse effects. We previously identified one of the Drosophila octopamine receptors named OAMB that produces increases in cAMP and intracellular Ca2+ upon ligand binding. It is expressed at high levels in the brain. To explore OAMB's physiological roles, we generated deletions in the OAMB locus. The resultant oamb mutants were viable without gross anatomical defects. The oamb females displayed normal courtship and copulation; however, they were impaired in ovulation with many mature eggs retained in their ovaries. RT-PCR, in situ hybridization, and expression of a reporter gene revealed that OAMB was also expressed in the thoracicoabdominal ganglion, the female reproductive system, and mature eggs in the ovary. Moreover, analysis of various alleles pinpointed the requirement for OAMB in the body, but not in the brain, for female fecundity. The novel expression pattern of OAMB and its genetic resource described in this study will help advance our understanding on how the neuromodulatory or endocrine system controls reproductive physiology and behavior.

Animals↗

PubMed2003

Integrin requirement for hippocampal synaptic plasticity and spatial memory.

The establishment of memory requires coordinated signaling between presynaptic and postsynaptic terminals in the CNS. The integrins make up a large family of cell adhesion receptors that are known to mediate bidirectional signaling between cells or between cells and their external environment. We show here that many different integrins, including alpha3 and alpha5, are expressed broadly in the adult mouse brain and are associated with synapses. Mice with genetically reduced expression of alpha3 integrin fail to maintain long-term potentiation (LTP) generated in hippocampal CA1 neurons. Mice with reduced expression of the alpha3 and alpha5 integrins exhibit a defect in paired-pulse facilitation. Mice with reduced expression of alpha3, alpha5, and alpha8 are defective in hippocampal LTP and spatial memory in the water maze but have normal fear conditioning. These results demonstrate that several different integrins are involved in physiological plasticity and provide the first evidence of their requirement for behavioral plasticity in vertebrates.

Animals↗

PubMed2003

An adjustable-threshold algorithm for the identification of objects in three-dimensional images.

MOTIVATION: To develop a highly accurate, practical and fast automated segmentation algorithm for three-dimensional images containing biological objects. To test the algorithm on images of the Drosophila brain, and identify, count and determine the locations of neurons in the images. RESULTS: A new adjustable-threshold algorithm was developed to efficiently segment fluorescently labeled objects contained within three-dimensional images obtained from laser scanning confocal microscopy, or two-photon microscopy. The result of the test segmentation with Drosophila brain images showed that the algorithm is extremely accurate and provided detailed information about the locations of neurons in the Drosophila brain. Centroids of each object (nucleus of each neuron) were also recorded into an algebraic matrix that describes the locations of the neurons. AVAILABILITY: Interested parties should send their request for the NeuronMapper(TM) program with the segmentation algorithm to artemp@bcm.tmc.edu.

Algorithms↗