The east gene of Drosophila melanogaster is expressed in the developing embryonic nervous system and is required for normal olfactory and gustatory responses of the adult

EAST and Chromator control the destruction and remodeling of muscles during Drosophila metamorphosis

Metamorphosis involves the destruction of larval, the formation of adult and the transformation of larval into adult tissues. In this study, we demonstrate the role of the Drosophila nuclear proteins EAST and Chromator in tissue destruction and remodeling. To better understand the function of east, we performed a yeast two-hybrid screen and identified the euchromatin associated protein Chromator as a candidate interactor. To analyze the functional significance of our two-hybrid data, we generated a set of novel pupal lethal Chro alleles by P-element excision. The pupal lethal Chro mutants resemble lethal east alleles as homozygous mutants develop into pharates with normal looking body parts, but fail to eclose. The eclosion defect of the Chro alleles is rescued in an east heterozygous background, indicating antagonistic genetic interactions between the two genes. Live cell imaging was applied to study muscle development during metamorphosis. Consistent with the eclosion defects, mutant pharates of both genes show loss and abnormal differentiation of adult eclosion muscles. The two genes have opposite effects on the destruction of larval muscles in metamorphosis. While Chro mutants show incomplete histolysis, muscles degenerate prematurely in east mutants. Moreover east mutants affect the remodeling of abdominal larval muscles into adult eclosion muscles. During this process, loss of east interferes with the spatial coordination of thinning of the larval muscles. Overexpression of EAST-GFP can prevent the disintegration of polytene chromosomes during programmed cell death. We propose that Chro activates and east inhibits processes and genes involved in tissue destruction and remodeling.

The extrachromosomal East protein of Drosophila can associate with polytene chromosomes and regulate gene expression

The EAST protein of Drosophila is a component of an expandable extrachromosomal domain of the nucleus. To better understand its function, we studied the dynamics and localization of GFP-tagged EAST. In live larval salivary glands, EAST-GFP is highly mobile and localizes to the extrachromosomal nucleoplasm. When these cells are permeabilized, EAST-GFP rapidly associated with polytene chromosomes. The affinity to chromatin increases and mobility decreases with decreasing salt concentration. Deleting the C-terminal residues 1535 to 2301 of EAST strongly reduces the affinity to polytene chromosomes. The bulk of EAST-GFP co-localizes with heterochromatin and is absent from transcriptionally active chromosomal regions. The predominantly chromosomal localization of EAST-GFP can be detected in non-detergent treated salivary glands of pupae as they undergo apoptosis, however not in earlier stages of development. Consistent with this chromosomal pattern of localization, genetic evidence indicates a role for EAST in the repression of gene expression, since a lethal east mutation is allelic to the viable mutation suppressor of white-spotted. We propose that EAST acts as an ion sensor that modulates gene expression in response to changing intracellular ion concentrations.

Experimental studies of adult Drosophila chemosensory behaviour

Drosophila melanogaster is a powerful animal model to study the processes underlying behavioural responses to chemical cues. This paper provides a review of the important literature to present recent advances in our understanding of how gustatory and olfactory stimuli are perceived. An overview is given of the experimental procedures currently used to characterize the fly chemosensory behaviour. Since this species provides extremely useful genetic tools, a focus is made on those allowing to manipulate behaviour, and hence to understand its molecular and cellular bases. Such tools include single-gene mutants and the Gal4/UAS system. They can be combined with studies of the natural polymorphism of behavioural responses. Recent data obtained with these various approaches unravel some important aspects of taste and olfaction. These appear as rather complex processes, as revealed by results showing dose-dependence, plasticity and sexual dimorphism. Taken together, these results and the available tools open interesting perspectives for the years to come, in our attempts to make the link between genes and behaviour.

The Drosophila EAST protein associates with a nuclear remnant during mitosis and constrains chromosome mobility

Drosophila EAST protein associates with an interior nonchromosomal compartment of the interphase nucleus. Because overexpression of east can dramatically alter nuclear architecture we investigated a potential role for EAST in changing chromosome organization during the cell cycle. Following nuclear envelope breakdown, EAST remains enriched in the mitotic remnant of the interphase nucleus until the onset of anaphase. Loss of east expression affects the accuracy of division cycles. In female meiosis, east mutations lead to abnormal segregation of nonexchange chromosomes. During the syncytial nuclear cycles, increased frequency of mitotic errors leads to the depletion of surface nuclei. In the post-syncytial cell cycles, abnormal congression of chromosomes in prometaphase delays the onset of anaphase. Loss of east expression also results in abnormal chromosome morphology in male meiosis. We propose that EAST constitutes a component of a nucleoskeleton that helps to constrain the mobility of chromosomes in interphase, mitosis and meiosis.

The EAST protein of drosophila controls an expandable nuclear endoskeleton

The high degree of structural order inside the nucleus suggests the existence of an internal nucleoskeleton. Our studies on the east gene of Drosophila, using the larval salivary gland polytene nucleus as a model, demonstrate the involvement of an extrachromosomal nuclear structure in modulating nuclear architecture. EAST, a novel ubiquitous protein, the product of the east (enhanced adult sensory threshold) locus, is localized to an extrachromosomal domain of the nucleus. Nuclear levels of EAST are increased in response to heat shock. Increase in nuclear EAST, whether caused by heat shock or by transgenic overexpression, results in the expansion of the extrachromosomal domain labelled by EAST, with a concomitant increase in the spacing between chromosomes. Moreover, EAST functions to promote the preferential accumulation of the proteins CP60 and actin in extrachromosomal regions of the nucleus. We propose that EAST mediates the assembly of an expandable nuclear endoskeleton which, through alterations of its volume, can modulate the spatial arrangement of chromosomes.

Functional complementation of the malvolio mutation in the taste pathway of Drosophila melanogaster by the human natural resistance-associated macrophage protein 1 (Nramp-1)

The malvolio (mvl) gene of Drosophila melanogaster encodes a protein with a high degree of homology to natural resistance-associated macrophage proteins (Nramps). This family of integral membrane proteins, many of which appear to function as cation transporters, is remarkably conserved in several phylogenetically distinct species. In Drosophila melanogaster, the protein Mvl is expressed in macrophages and in differentiated neurons; loss-of-function mutations lead to defects in gustatory behaviour. The human Nramp-1 protein was expressed in Drosophila melanogaster using the hsp70 promoter. Overexpression in normal animals does not lead to any alterations in their behaviour or physiology. In mutants, however, ubiquitous expression of human Nramp-1 can totally rescue the taste defect. This finding that Nramp-1 can complement the taste defect in mvl mutants provides a potent means of exploiting behavioural genetics to dissect the function of Nramp-1 and to identify other molecules involved with this transport system.

Mutations in masquerade, a novel serine-protease-like molecule, affect axonal guidance and taste behavior in Drosophila

The masquerade (mas) locus encodes an extracellular molecule with a striking similarity to serine proteases. The serine residue, which is essential for enzymatic activity, has been substituted by glycine, suggesting that MAS could serve to antagonize serine protease activity [Murugasu-Oei et al. (1995), Genes Dev. 9, 139-154]. We describe the expression pattern of mas mRNA and protein in the developing embryonic, larval and pupal nervous system and in the epidermis. Total loss of mas function is lethal and results in aberrations in the embryonic central and peripheral nervous systems, consistent with a role in axonal guidance. The possibility that the observed deficits in taste behavior, exhibited by animals with partial loss of mas function, are a result of defects in the adult brain are discussed.

Olfaction in Drosophila: from odor to behavior

Odors elicit a variety of behavioral responses from Drosophila via a relatively simple, but sensitive, olfactory system. An increasing number of mutants have been found to be defective in olfactory function. Genetic and molecular analyses of the Drosophila olfactory system have identified some of its molecular components, and have revealed some principles of its function and organization.

Scutoid mutation of Drosophila melanogaster specifically decreases olfactory responses to short-chain acetate esters and ketones

A molecular-genetic approach has been taken to identify genes involved in olfactory transduction in Drosophila melanogaster. Two independent lines of research led to the finding that the dominant Scutoid (Sco) mutation causes a diminished extracellular electroantennogram response to the odorants ethyl acetate (EtAC) and acetone (AC). Sco flies showed about 4- and 2.5-fold reduced responses to EtAC and AC, respectively, compared to Canton-S wild-type and sibling control flies lacking the Sco mutation when electroantennogram recordings were made from the proximal anterior third antennal segment. The responses to five other odors from three different chemical classes were unaltered. The maximum response to either EtAC or AC was decreased with no change in apparent affinity. Responses to short-chain (but not long-chain) acetate esters and ketones were dramatically affected at all antennal locations tested. Only in the proximal quadrants were responses to ethyl acetoacetate also reduced. Most Sco revertants tested had a normal olfactory response; duplications of the region including no-ocelli partially suppress the Sco bristle as well as olfactory phenotypes. Sco adults had an impaired behavioral response to EtAC but not to banana or propionate. There was no effect of the mutation on larval chemosensory behavior or extracellularly recorded adult compound eye and ocellar visual responses. These findings suggest the involvement of Sco in an olfactory pathway in adults which is specific for short-chain acetate esters and ketones.

Genetic determinants of sense organ identity in Drosophila: regulatory interactions between cut and poxn

Two genes involved in defining the type of sense organ have been identified in Drosophila. The gene cut differentiates the external sense organs (where it is expressed) from the chordotonal organs (where it is not); among the external sense organs poxn differentiates the poly-innervated organs (where it is expressed) from the mono-innervated organs (where it is not). Here we show that the expression of poxn in normal embryos does not depend on cut, and that poxn is capable of inducing the expression of cut. We have identified a small domain of the very large cut regulatory region as a likely target for activation by poxn.

Members of a family of Drosophila putative odorant-binding proteins are expressed in different subsets of olfactory hairs

A polymerase chain reaction-based method was used to generate a Drosophila melanogaster antennal cDNA library from which head cDNAs were subtracted. We identified five cDNAs that code for antennal proteins containing six cysteines in a conserved pattern shared with known moth antennal proteins, including pheromone-binding proteins. Another cDNA codes for a protein related to vertebrate brain proteins that bind hydrophobic ligands. In all, we describe seven antennal proteins which contain potential signal peptides, suggesting that, like pheromone-binding proteins, they may be secreted in the lumen of olfactory hairs. The expression patterns of these putative odorant-binding proteins define at least four different subsets of olfactory hairs and suggest that the Drosophila olfactory apparatus is functionally segregated.

The Drosophila homolog of the human transcription factor TEF-1, scalloped, is essential for normal taste behavior

The scalloped (sd) locus of Drosophila melanogaster encodes a protein with a novel DNA binding domain bearing a high degree of similarity to the human transcription factor TEF-1 (Campbell et al., 1992). We demonstrate that sd mutants show defects in response to a number of taste stimuli. Higher stimulus concentrations are required to elicit behavioral responses from mutant larvae and adult flies. The electrophysiological responses of the peripheral taste neurons in the labellum were found to be normal, suggesting that an inability to detect stimuli is not the cause of the mutant phenotype. The range of mutant responses of sd alleles to salt and sugar stimuli define a functional requirement for the gene in the nervous system and provide an assay for the genetic and molecular analysis of this role.