Veronica Rodrigues

malvolio, the Drosophila homologue of mouse NRAMP-1 (Bcg), is expressed in macrophages and in the nervous system and is required for normal taste behaviour.

We report the sequence, expression pattern and mutant phenotype of malvolio (mvl), the Drosophila homologue of mammalian natural resistance‐associated macrophage proteins (NRAMPs). In the mouse, this novel transporter is encoded by Bcg, a dominant gene that confers natural resistance to intracellular parasites. mvl was identified in a screen for mutants that affect taste behaviour. We show that loss‐of‐function as well as insertional mutants in mvl display defects in taste behaviour with no alterations in the physiology of the sensory neurons. Activity of the reporter enzyme beta‐galactosidase, that reflects the expression pattern of mvl, is seen in mature sensory neurons and in macrophages. The conceptual translation of the mvl cDNA shows a striking similarity (65% identity) with human NRAMP with almost complete identity in a conserved consensus motif found in a number of ATP‐coupled transporters. Based on its phenotype and expression pattern as well as its structural similarities to NRAMPs and a nitrate transporter in Aspergillus nidulans, we discuss a possible role for MVL in nitrite/nitrate transport and its implications.

Genetic analysis of chemosensory pathway

Some olfactory and gustatory mutants ofDrosophila melanogaster are described. Theolf mutants are insensitive to the repellent, benzaldehyde or the attractant ethyl acetate or simultaneously to both. Thegust mutants are unable to taste quinine or NaCl or sucrose. Electrophysiological tests show that one of the sugar non-tasters has an altered primary chemoreceptor response to sucrose.

atonal is a proneural gene for a subset of olfactory sense organs in Drosophila

Background: The antenna of the adult fruit fly, Drosophila melanogaster, is covered with three morphologically distinct types of olfactory sense organs. In addition, mechano‐ and hygro‐sensitive receptors are also present on its surface. While much has been learnt about the development of peripheral nervous system in Drosophila, the mechanisms underlying the development of olfactory sensilla are just beginning to be unraveled. The antennal sense organs have several properties that make them distinct from other sense organs. While each sensillum type is arranged in a well‐defined region of the antenna, the position of an individual sensillum is not fixed. The development of these sense organs appears to combine an initial step of cell recruitment, as in photoreceptors, followed by cell lineage mechanisms, as in the development of other external sense organs. The earliest step in development, the selection of a sensory organ precursor, involves the interaction of proneural and neurogenic genes. The proneural gene for the antennal sense organs has been elusive so far.

The Ataxin-2 protein is required for microRNA function and synapse-specific long-term olfactory habituation

Local control of mRNA translation has been proposed as a mechanism for regulating synapse-specific plasticity associated with long-term memory. We show here that glomerulus-selective plasticity of Drosophila multiglomerular local interneurons observed during long-term olfactory habituation (LTH) requires the Ataxin-2 protein (Atx2) to function in uniglomerular projection neurons (PNs) postsynaptic to local interneurons (LNs). PN-selective knockdown of Atx2 selectively blocks LTH to odorants to which the PN responds and in addition selectively blocks LTH-associated structural and functional plasticity in odorant-responsive glomeruli. Atx2 has been shown previously to bind DEAD box helicases of the Me31B family, proteins associated with Argonaute (Ago) and microRNA (miRNA) function. Robust transdominant interactions of atx2 with me31B and ago1 indicate that Atx2 functions with miRNA-pathway components for LTH and associated synaptic plasticity. Further direct experiments show that Atx2 is required for miRNA-mediated repression of several translational reporters in vivo. Together, these observations (i) show that Atx2 and miRNA components regulate synapse-specific long-term plasticity in vivo; (ii) identify Atx2 as a component of the miRNA pathway; and (iii) provide insight into the biological function of Atx2 that is of potential relevance to spinocerebellar ataxia and neurodegenerative disease.

Genetics of Olfactory Behavior in Drosophila Melanogaster

We have used a behavioral genetic approach to identify six X-linked loci which specify olfaction in Drosophila melanogaster. Mutations in five of these genes lead to partial anosmias affecting responses either to aldehydes (olfA, olfB, olfE and olfF) or to acetate esters (olfC). Only one of the mutants obtained in our screening (olfD) resulted in a insensitivity to several different odorants. olfA, olfE and olfC map close together in a small region of the chromosome between 7C and 7D. The alleles at the olfC locus fall into two phenotypic classes according to their responses to different acetate esters. The two groups of olfC alleles interact in-trans.

Reduced Odor Responses from Antennal Neurons of Gqα, Phospholipase Cβ, and rdgA Mutants in Drosophila Support a Role for a Phospholipid Intermediate in Insect Olfactory Transduction

Mechanisms by which G-protein-coupled odorant receptors transduce information in insects still need elucidation. We show that mutations in the Drosophila gene for Gqα (dgq) significantly reduce both the amplitude of the field potentials recorded from the whole antenna in responses to odorants as well as the frequency of evoked responses of individual sensory neurons. This requirement for Gqα is for adult function and not during antennal development. Conversely, brief expression of a dominant-active form of Gqα in adults leads to enhanced odor responses. To understand signaling downstream of Gqα in olfactory sensory neurons, genetic interactions of dgq were tested with mutants in genes known to affect phospholipid signaling. dgq mutant phenotypes were further enhanced by mutants in a PLCβ (phospholipase Cβ) gene, plc21C. Interestingly although, the olfactory phenotype of mutant alleles of diacylglycerol kinase (rdgA) was rescued by dgq mutant alleles. Our results suggest that Gqα-mediated olfactory transduction in Drosophila requires a phospholipid second messenger the levels of which are regulated by a cycle of phosphatidylinositol 1,4-bisphosphate breakdown and regeneration.

Plasticity of local GABAergic interneurons drives olfactory habituation

Despite its ubiquity and significance, behavioral habituation is poorly understood in terms of the underlying neural circuit mechanisms. Here, we present evidence that habituation arises from potentiation of inhibitory transmission within a circuit motif commonly repeated in the nervous system. In Drosophila, prior odorant exposure results in a selective reduction of response to this odorant. Both short-term (STH) and long-term (LTH) forms of olfactory habituation require function of the rutabaga-encoded adenylate cyclase in multiglomerular local interneurons (LNs) that mediate GABAergic inhibition in the antennal lobe; LTH additionally requires function of the cAMP response element-binding protein (CREB2) transcription factor in LNs. The odorant selectivity of STH and LTH is mirrored by requirement for NMDA receptors and GABAA receptors in odorant-selective, glomerulus-specific projection neurons(PNs). The need for the vesicular glutamate transporter in LNs indicates that a subset of these GABAergic neurons also releases glutamate. LTH is associated with a reduction of odorant-evoked calcium fluxes in PNs as well as growth of the respective odorant-responsive glomeruli. These cellular changes use similar mechanisms to those required for behavioral habituation. Taken together with the observation that enhancement of GABAergic transmission is sufficient to attenuate olfactory behavior, these data indicate that habituation arises from glomerulus-selective potentiation of inhibitory synapses in the antennal lobe. We suggest that similar circuit mechanisms may operate in other species and sensory systems.

A gustatory mutant of Drosophila defective in pyranose receptors

SummaryMutations in an X-linked gene, gust-A, block the responses of Drosophila melanogaster to a group of pyranose sugars. It is shown that the behavioural effects of this mutation are correlated with a loss of electrical responses in taste receptors. The mutation affects the chemoacceptors for pyranose sugars leaving the furanose acceptors intact.

Drosophila olfactory local interneurons and projection neurons derive from a common neuroblast lineage specified by the empty spiracles gene

BackgroundEncoding of olfactory information in insects occurs in the antennal lobe where the olfactory receptor neurons interact with projection neurons and local interneurons in a complex sensory processing circuitry. While several studies have addressed the developmental mechanisms involved in specification and connectivity of olfactory receptor neurons and projection neurons in Drosophila, the local interneurons are far less well understood.ResultsIn this study, we use genetic marking techniques combined with antibody labelling and neuroblast ablation to analyse lineage specific aspects of local interneuron development. We find that a large set of local interneurons labelled by the GAL4-LN1 (NP1227) and GAL4-LN2 (NP2426) lines arise from the lateral neuroblast, which has also been shown to generate uniglomerular projection neurons. Moreover, we find that a remarkable diversity of local interneuron cell types with different glomerular innervation patterns and neurotransmitter expression derives from this lineage. We analyse the birth order of these two distinct neuronal types by generating MARCM (mosaic analysis with a repressible cell marker) clones at different times during larval life. This analysis shows that local interneurons arise throughout the proliferative cycle of the lateral neuroblast beginning in the embryo, while uniglomerular projection neurons arise later during the second larval instar. The lateral neuroblast requires the function of the cephalic gap gene empty spiracles for the development of olfactory interneurons. In empty spiracles null mutant clones, most of the local interneurons and lateral projection neurons are lacking. These findings reveal similarities in the development of local interneurons and projection neurons in the olfactory system of Drosophila.ConclusionWe find that the lateral neuroblast of the deutocerebrum gives rise to a large and remarkably diverse set of local interneurons as well as to projection neurons in the antennal lobe. Moreover, we show that specific combinations of these two neuron types are produced in specific time windows in this neuroblast lineage. The development of both these cell types in this lineage requires the function of the empty spiracles gene.

Olfactory Behavior of Drosophila Melanogaster

The olfactory system of Drosophila is readily amenable to genetic dissection. The response to smell involves interaction between a chemical stimulant and the receptor surface, transduction, neural excitation, transmission across synapses and integration by the central nervous system finally leading to motor activity. By an appropriate choice of mutants, attention can be focussed on any one of this series of complex processes. In this paper I will describe the properties of olfactory mutations on the X-chromosome and compare the behavior of mutants with normal flies.