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Touch sensation is essential for behaviours ranging from environmental exploration to social interaction; however, the underlying mechanisms are largely unknown (1).In Drosophila larvae, two types of sensory neurons, class III [...]

Detailed chromosome maps with reliable homologies among chromosomes of different species are the first step to study the evolution of the genetic architecture in any set of species. Here, we present detailed photo maps of the polytene chromosomes of three closely related species of the tripunctata group (subgenus Drosophila): Drosophila mediopunctata, D. roehrae, and D. unipunctata. We identified Muller's elements in each species, using FISH, establishing reliable chromosome homologies among species and D. melanogaster. The simultaneous analysis of chromosome inversions revealed a distribution pattern for the inversion polymorphisms among Muller's elements in the three species. Element E is the most polymorphic, with many inversions in each species. Element C follows; while the least polymorphic elements are B and D. While interesting, it remains to be determined how general this pattern is among species of the tripunctata group. Despite previous studies showing that D. mediopunctata and D. unipunctata are phylogenetically closer to each other than to D. roehrae, D. unipunctata shows rare karyotypic changes. It has two chromosome fusions: an additional heterochromatic chromosome pair and a pericentric inversion in the X chromosome. This especial conformation suggests a fast chromosomal evolution that deserves further study. Key words: chromosomes, photo maps, Muller's elements, fluorescence in situ hybridization. Des cartes chromosomiques detaillees fournissant des informations fiables sur l'homologie entre les chromosomes de diverses especes constituent une premiere etape dans l'etude de revolution de l'architecture genomique chez n'importe quel groupe d'especes. Ici, les auteurs presentent des photographies detaillees des chromosomes polytenes de trois especes proches au sein du groupe tripunctata (sous-genre Drosophila): Drosophila mediopunctata, D. roehrae et D. unipunctata. Les auteurs identifient les elements de Muller au sein de chaque espece au moyen d'analyses FISH afin d'etablir clairement les relations d'homologie entre les chromosomes de ces especes et D. melanogaster. L'analyse simultanee des inversions chromosomiques a revele la distribution des polymorphismes d'inversion au sein des elements de Muller chez ces trois especes. L'element E est le plus polymorphe et presente de nombreuses inversions chez chaque espece. L'element C est le suivant, tandis que les elements B et D sont les moins polymorphes. Bien qu'interessant il reste a determiner dans quelle mesure ces observations sont generales au sein des especes du groupe tripunctata. En depit d'etudes anterieures ayant montre que les especes D. mediopunctata et D. unipunctata sont plus proches entre elles que du D. roehrae,leD. unipunctata presente des changements caryotypiques rares. Il presente deux fusions chromosomiques, une paire additionnelle de chromosomes heterochromatiques et une inversion pericentrique au sein du chromosome X. Cette conformation particuliere suggere une evolution chromosomique rapide qui merite des etudes additionnelles. [Traduit par la Redaction] Mots-cles: chromosomes, cartes photo, elements de Muller, hybridation in situ en fluorescence., Introduction The pioneering study by Metz (1914), which compared metaphase karyotypes in the genus Drosophila, combined with subsequent comparative genetic studies showed that the integrity of the arms of chromosomes [...]

The odour of acids has a distinct quality that is perceived as sharp, pungent and often irritating (1). How acidity is sensed and translated into an appropriate behavioural response is poorly understood. Here we describe a functionally segregated population of olfactory sensory neurons in the fruitfly, Drosophila melanogaster, that are highly selective for acidity. These olfactory sensory neurons express IR64a, a member of the recently identified ionotropic receptor (IR) family of putative olfactory receptors (2). In vivo calcium imaging showed that IR64a+ neurons projecting to the DC4 glomerulus in the antennal lobe are specifically activated by acids. Flies in which the function of IR64a+ neurons or the IR64a gene is disrupted had defects in acid-evoked physiological and behavioural responses, but their responses to non-acidic odorants remained unaffected. Furthermore, artificial stimulation of IR64a+ neurons elicited avoidance responses. Taken together, these results identify cellular and molecular substrates for acid detection in the Drosophila olfactory system and support a labelled-line mode of acidity coding at the periphery., Many aversive odorants activate combinations of olfactory sensory neurons (OSNs) (3,4), complicating the dissection of the circuits that translate odour recognition into behaviour. By contrast, carbon dioxide (C[O.sub.2]), an odorant [...]

This review in two parts deals with the increasing number of processes known to be used by eukaryotic cells to protect gene expression from undesired genomic enhancer or chromatin effects, by means of the so-called insulators or barriers. The most advanced studies in this expanding field concern yeasts and Drosophila (this article) and the vertebrates (next article in this issue). Clearly, the cell makes use of every gene context to find the appropriate, economic, solution. Thus, besides the elements formerly identified and specifically dedicated to insulation, a number of unexpected elements are diverted from their usual function to structure the genome and enhancer action or to prevent heterochromatin spreading. They are, for instance, genes actively transcribed by RNA polymerase II or III, partial elements of these transcriptional machineries (stalled RNA polymerase II, normally required by genes that must respond quickly to stimuli, or TFIIIC bound at its B-box, normally required by RNA polymerase III for assembly of the transcription initiation complex at tRNA genes), or genomic sequences occupied by variants of standard histones, which, being rapidly and permanently replaced, impede heterochromatin formation. Key words: gene insulation, DNA looping, MAT locus, hox, gypsy, scs/scs', heat shock. Cette revue en deux parties, repertorie les moyens de plus en plus nombreux employes par la cellule eucaryote pour proteger l'expression d'un gene des effets genomiques indesirables, effets de regulation a distance ou effets chromatiniens, au moyen d'isolateurs ou de barrieres. Les etudes les plus poussees dans ce domaine en pleine expansion, concerne les levures et la mouche drosophile (cet article), ainsi que les vertebres (article suivant). Il apparait que la cellule fonctionne avec une economie de moyens pour trouver la solution la plus appropriee a un cas donne;. Ainsi a cote des elements anciennement identifies et specifiquement dediesa l'isolation, un certain nombre d'elements inattendus sont detournes de leur fonction usuelle de maniere a structurer le genome et l'action d'enhancers, ou pour interrompre la propagation d'heterochromatine. Les isolateurs recemment mis a jour, sont par exemple, des genes activement transcrits par l'ARN polymerase II comme l'ARN polymerase III, des elements isoles de leurs machineries transcriptionnelles (l'ARN polymerase II en pause normalement requise par les genes qui doivent repondre rapidement a des stimuli, ou le facteur TFIIIC sur sa boite B, normalement requis par l'ARN polymerase III pour l'assemblage du complexe d'initiation aux genes de transfert tARN), ou encore, des sequences genomiques occupees par des variantes d'histones standard, qui en etant remplacees de maniere permanente, empechent la formation de chromatine condensee. Mots-cles: isolateurs, action a distance, MAT, hox, gypsy, choc thermique., Introduction In eukaryotes, expression of a gene is generally restricted to specific tissues, to specific stages of development, or to specific environmental conditions. Some situations also require that a given [...]

Genes include cis-regulatory regions that contain transcriptional enhancers. Recent reports have shown that developmental genes often possess multiple discrete enhancer modules that drive transcription in similar spatio-temporal patterns (1-4): primary enhancers located near the basal promoter and secondary, or 'shadow', enhancers located at more remote positions. It has been proposed that the seemingly redundant activity of primary and secondary enhancers contributes to phenotypic robustness (1,5). We tested this hypothesis by generating a deficiency that removes two newly discovered enhancers of shavenbaby (svb, a transcript of the ovo locus), a gene encoding a transcription factor that directs development of Drosophila larval trichomes (6). At optimal temperatures for embryonic development, this deficiency causes minor defects in trichome patterning. In embryos that develop at both low and high extreme temperatures, however, absence of these secondary enhancers leads to extensive loss of trichomes. These temperature-dependent defects can be rescued by a transgene carrying a secondary enhancer driving transcription of the svb cDNA. Finally, removal of one copy of wingless, a gene required for normal trichome patterning (7), causes a similar loss of trichomes only in flies lacking the secondary enhancers. These results support the hypothesis that secondary enhancers contribute to phenotypic robustness in the face of environmental and genetic variability., The cis-regulatory region of the svb gene integrates inputs from multiple gene regulatory networks to generate a complex pattern of expression in the embryonic epidermis of insect species (6,8). SVB [...]

Acetylation within the globular core domain of histone H3 on lysine 56 (H3K56) has recently been shown to have a critical role in packaging DNA into chromatin following DNA replication and repair in budding yeast (1,2). However, the function or occurrence of this specific histone mark has not been studied in multicellular eukaryotes, mainly because the Rtt109 enzyme that is known to mediate acetylation of H3K56 (H3K56ac) is fungal-specific (3,4). Here we demonstrate that the histone acetyl transferase CBP (also known as Nejire) in flies and CBP and p300 (Ep300) in humans acetylate H3K56, whereas Drosophila Sir2 and human SIRT1 and SIRT2 deacetylate H3K56ac. The histone chaperones ASF1A in humans and Asf1 in Drosophila are required for acetylation of H3K56 in vivo, whereas the histone chaperone CAF-1 (chromatin assembly factor 1) in humans and Caf1 in Drosophila are required for the incorporation of histones bearing this mark into chromatin. We show that, in response to DNA damage, histones bearing acetylated K56 are assembled into chromatin in Drosophila and human cells, forming foci that colocalize with sites of DNA repair. Furthermore, acetylation of H3K56 is increased in multiple types of cancer, correlating with increased levels of ASF1A in these tumours. Our identification of multiple proteins regulating the levels of H3K56 acetylation in metazoans will allow future studies of this critical and unique histone modification that couples chromatin assembly to DNA synthesis, cell proliferation and cancer., H3K56 acetylation has a critical role in regulating chromatin assembly following DNA synthesis (1,2), chromatin disassembly during transcriptional activation (5) and cell survival (1) in yeast. Although H3K56ac clearly exists [...]

Hedgehog (Hh) signalling is essential for several aspects of embryogenesis (1,2). In Drosophila, Hh transduction is mediated by a cytoplasmic signalling complex (3-5) that includes the putative serine-threonine kinase Fused [...]

The segregation of axon and dendrite projections into distinct synaptic layers is a fundamental principle of nervous system organization and the structural basis for information processing in the brain (1). [...]

Byline: Hao Zheng (Department of Biology and Center for Research on Biological Clocks, Texas A&M University, College Station, TX, USA, Department of Biology and Biochemistry, University of Houston, Houston, TX, [...]

The Hedgehog (Hh) signaling pathway is intimately Linked to cell growth and differentiation, with normal roles in embryonic pattern formation and adult tissue homeostasis and pathological roles in tumor initiation and growth. Recent advances in our understanding of Hh response have resulted from the identification of new pathway components and new mechanisms of action for old pathway components. The most striking new finding is that signal transmission from membrane to cytoplasm proceeds through recruitment, by the seven-transmembrane protein Smoothened, of an atypical kinesin, which routes pathway activation by interaction with other components of a complex that includes the latent zinc finger transcription factor. Ci., The expression and activity of Hedgehog proteins (Hh) exemplify a common strategy for pattern generation in metazoan embryos, namely, the specification of multiple cell fates through localized production and secretion [...]

Author(s): Fayyaz S. Sutterwala [1]; Richard A. Flavell [2] The availability of powerful genetic tools to study the fruitfly Drosophila melanogaster , and the striking similarities of this insect's immune [...]

Reduced activity of the insulin/insulin-like growth factor signaling (IIS) pathway extends life-span in the worm, fly, and mouse and can also lower fecundity (1-3). How the evolutionarily conserved effects of [...]