Representation of the glomerular olfactory map in the Drosophila brain

We explored how the odor map in the Drosophila antennal lobe is represented in higher olfactory centers, the mushroom body and lateral horn. Systematic single-cell tracing of projection neurons (PNs) that send dendrites to specific glomeruli in the antennal lobe revealed their stereotypical axon branching patterns and terminal fields in the lateral horn. PNs with similar axon terminal fields tend to receive input from neighboring glomeruli. The glomerular classes of individual PNs could be accurately predicted based solely on their axon projection patterns. The sum of these patterns defines an "axon map" in higher olfactory centers reflecting which olfactory receptors provide input. This map is characterized by spatial convergence and divergence of PN axons, allowing integration of olfactory information.     

A map of olfactory representation in the Drosophila mushroom body

Neural coding for olfactory sensory stimuli has been mapped near completion in the Drosophila first-order center, but little is known in the higher brain centers. Here, we report that the antenna lobe (AL) spatial map is transformed further in the calyx of the mushroom body (MB), an essential olfactory associated learning center, by stereotypic connections with projection neurons (PNs). We found that Kenyon cell (KC) dendrites are segregated into 17 complementary domains according to their neuroblast clonal origins and birth orders. Aligning the PN axonal map with the KC dendritic map and ultrastructural observation suggest a positional ordering such that inputs from the different AL glomeruli have distinct representations in the MB calyx, and these representations might synapse on functionally distinct KCs. Our data suggest that olfactory coding at the AL is decoded in the MB and then transferred via distinct lobes to separate higher brain centers.     

PDF cycling in the dorsal protocerebrum of the Drosophila brain is not necessary for circadian clock function

In Drosophila, the neuropeptide pigment-dispersing factor (PDF) is a likely circadian molecule, secreted by central pacemaker neurons (LNvs). PDF is expressed in both small and large LNvs (sLNvs and lLNvs), and there are striking circadian oscillations of PDF staining intensity in the small cell termini, which require a functional molecular clock. This cycling may be relevant to the proposed role of PDF as a synchronizer of the clock system or as an output signal connecting pacemaker cells to locomotor activity centers. In this study, the authors use a generic neuropeptide fusion protein (atrial natriuretic factor-green fluorescent protein [ANF-GFP]) and show that it can be expressed in the same neurons as PDF itself. Yet, ANF-GFP as well as PDF itself does not manifest any cyclical accumulation in sLNv termini in adult transgenic flies. Surprisingly, the absence of detectable PDF cycling is not accompanied by any detectable behavioral pheno-type, since these transgenic flies have normal morning and evening anticipation in a light-dark cycle (LD) and are fully rhythmic in constant darkness (DD). The molecular clock is also not compromised. The results suggest that robust PDF cycling in sLNv termini plays no more than a minor role in the Drosophila circadian system and is apparently not even necessary for clock output function.     

A map of taste neuron projections in the Drosophila CNS

We provide a map of the projections of taste neurons in the CNS of Drosophila. Using a collection of 67 GAL4 drivers representing the entire repertoire of Gr taste receptors, we systematically map the projections of neurons expressing these drivers in the thoracico-abdominal ganglion and the suboesophageal ganglion (SOG). We define 9 categories of projections in the thoracico-abdominal ganglia and 10 categories in the SOG. The projection patterns are modular, and can be interpreted as combinations of discrete pattern elements. The elements can be interpreted in terms of the taste organ from which the projections originate, the structures from which they originate, and the quality of taste information that they represent. The extensive diversity in projection patterns provides an anatomical basis for functional diversity in responses elicited by different taste stimuli.     

Towards a Drosophila genome map.

A physical map of the genome of Drosophila melanogaster has been created using 965 yeast artificial chromosome (YAC) clones assigned to locations in the cytogenetic map by in situ hybridization with the polytene salivary gland chromosomes. Clones with insert sizes averaging about 200 kb, totaling 1.7 genome equivalents, have been mapped. More than 80% of the euchromatic genome is included in the mapped clones, and 75% of the euchromatic genome is included in 161 cytological contigs ranging in size up to 2.5 Mb (average size 510 kb). On the other hand, YAC coverage of the one-third of the genome constituting the heterochromatin is incomplete, and clones containing long tracts of highly repetitive simple satellite DNA sequences have not been recovered.     

A fine-structure gynandromorph fate map of the Drosophila head

A gynandromorph fate map of the head of D. melanogaster was produced using 28 landmarks derived from one imaginal disc. An examination of the meaning of fine-structure mapping discloses that the sturt value observed between one pair of landmarks within a disc may approximate the relative physical distance of their progenitor cells at blastoderm, but for another pair of landmarks (assuming no directed cell movements), the sturt value may simply reflect their close geographic location at the time the cells are specified for their particular differentiation, a time much later in development when most cell division within the disc has come to an end. The formation of early developmental compartments has little effect on fate-map distances. Our analysis of the data suggests there are approximately ten cells present at the blastoderm stage that are head progenitors. Each blastoderm cell is likely to be the progenitor of a particular array of landmarks, but there is overlap between arrays from different blastoderm cells.     

A microsatellite linkage map of Drosophila mojavensis

Background

Drosophila mojavensishas been a model system for genetic studies of ecological adaptation and speciation. However, despite its use for over half a century, no linkage map has been produced for this species or its close relatives.

Results

We have developed and mapped 90 microsatellites in D. mojavensis, and we present a detailed recombinational linkage map of 34 of these microsatellites. A slight excess of repetitive sequence was observed on the X-chromosome relative to the autosomes, and the linkage groups have a greater recombinational length than the homologous D. melanogaster chromosome arms. We also confirmed the conservation of Muller's elements in 23 sequences between D. melanogaster and D. mojavensis.

Conclusions

The microsatellite primer sequences and localizations are presented here and made available to the public. This map will facilitate future quantitative trait locus mapping studies of phenotypes involved in adaptation or reproductive isolation using this species.     

Misexpression screen for genes altering the olfactory map in Drosophila

Despite the identification of a number of guidance molecules, a comprehensive picture has yet to emerge to explain the precise anatomy of the olfactory map. From a misexpression screen of 1,515 P{GS} lines, we identified 23 genes that, when forcibly expressed in the olfactory receptor neurons, disrupted the stereotyped anatomy of the Drosophila antennal lobes. These genes, which have not been shown previously to control olfactory map development, encode novel proteins as well as proteins with known roles in axonal outgrowth and cytoskeletal remodeling. We analyzed Akap200, which encodes a Protein Kinase A-binding protein. Overexpression of Akap200 resulted in fusion of the glomeruli, while its loss resulted in misshapen and ectopic glomeruli. The requirement of Akap200 validates our screen as an effective approach for recovering genes controlling glomerular map patterning. Our finding of diverse classes of genes reveals the complexity of the mechanisms that underlie olfactory map development.     

Activity-independent prespecification of synaptic partners in the visual map of Drosophila

Specifying synaptic partners and regulating synaptic numbers are at least partly activity-dependent processes during visual map formation in all systems investigated to date . In Drosophila, six photoreceptors that view the same point in visual space have to be sorted into synaptic modules called cartridges in order to form a visuotopically correct map . Synapse numbers per photoreceptor terminal and cartridge are both precisely regulated . However, it is unknown whether an activity-dependent mechanism or a genetically encoded developmental program regulates synapse numbers. We performed a large-scale quantitative ultrastructural analysis of photoreceptor synapses in mutants affecting the generation of electrical potentials (norpA, trp;trpl), neurotransmitter release (hdc, syt), vesicle endocytosis (synj), the trafficking of specific guidance molecules during photoreceptor targeting (sec15), a specific guidance receptor required for visual map formation (Dlar), and 57 other novel synaptic mutants affecting 43 genes. Remarkably, in all these mutants, individual photoreceptors form the correct number of synapses per presynaptic terminal independently of cartridge composition. Hence, our data show that each photoreceptor forms a precise and constant number of afferent synapses independently of neuronal activity and partner accuracy. Our data suggest cell-autonomous control of synapse numbers as part of a developmental program of activity-independent steps that lead to a "hard-wired" visual map in the fly brain.     

Proteome reference map of Drosophila melanogaster head

Drosophila melanogaster has been used as a genetic model organism to understand the fundamental molecular mechanisms in human biology including memory formation that has been reported involving protein synthesis and/or post-translational modification. In this study, we employed a proteomic platform based on fluorescent 2DE and MALDI-TOF MS to build a standard D. melanogaster head proteome map for proteome-proteome comparison. In order to facilitate the comparison, an interactive database has been constructed for systematically integrating and analyzing the proteomes from different conditions and further implicated to study human diseases related to D. melanogaster model. In summary, the fundamental head proteomic database and bioinformatic analysis will be useful for further elucidating the biological mechanisms such as memory formation and neurodegenerative diseases.     

A rapid method to map mutations in Drosophila

Background

Genetic screens in Drosophila have provided a wealth of information about a variety of cellular and developmental processes. It is now possible to screen for mutant phenotypes in virtually any cell at any stage of development by performing clonal screens using the flp/FRT system. The rate-limiting step in the analysis of these mutants is often the identification of the mutated gene, however, because traditional mapping strategies rely mainly on genetic and cytological markers that are not easily linked to the molecular map.

Results

Here we describe the development of a single-nucleotide polymorphism (SNP) map for chromosome arm 3R. The map contains 73 polymorphisms between the standard FRT chromosome, and a mapping chromosome that carries several visible markers (rucuca), at an average density of one SNP per 370 kilobases (kb). Using this collection, we show that mutants can be mapped to a 400 kb interval in a single meiotic mapping cross, with only a few hundred SNP detection reactions. Discovery of further SNPs in the region of interest allows the mutation to be mapped with the same recombinants to a region of about 50 kb.

Conclusion

The combined use of standard visible markers and molecular polymorphisms in a single mapping strategy greatly reduces both the time and cost of mapping mutations, because it requires at least four times fewer SNP detection reactions than a standard approach. The use of this map, or others developed along the same lines, will greatly facilitate the identification of the molecular lesions in mutants from clonal screens.     

A spatial map of olfactory receptor expression in the Drosophila antenna

Insects provide an attractive system for the study of olfactory sensory perception. We have identified a novel family of seven transmembrane domain proteins, encoded by 100 to 200 genes, that is likely to represent the family of Drosophila odorant receptors. Members of this gene family are expressed in topographically defined subpopulations of olfactory sensory neurons in either the antenna or the maxillary palp. Sensory neurons express different complements of receptor genes, such that individual neurons are functionally distinct. The isolation of candidate odorant receptor genes along with a genetic analysis of olfactory-driven behavior in insects may ultimately afford a system to understand the mechanistic link between odor recognition and behavior.     

Toward an energy function for the contact map representation of proteins

We analyzed several energy functions for predicting the native state of proteins from an energy minimization procedure. We derived the parameters of a given energy function by imposing the basic requirement that the energy of the native conformation of a protein is lower than that of any conformation chosen from a set of decoys. Our work is motivated by a recent result which proved that the simple pairwise contact approximation of the energy is insufficient to satisfy simultaneously such a basic requirement for all the proteins in a database. Here, we investigate the reasons of such negative results and show how to improve the predictive power of methods based on energy minimization. We generated decoys by gapless threading, and we derive energy parameters by perceptron learning. We first considered hydrophobic contributions to the energy, defined in several ways, and showed that the additional hydrophobic terms enlarge slightly the number of proteins that can be stabilized together. Next, we performed various modifications of the pairwise energy term. We introduced (1) a distinction between inter-residue contacts on the surface and in the core of a protein and (2) a simple distance-dependent pairwise interaction in which a two-tier definition of contact replaces the original (single-tier) one. Our results suggest that a detailed treatment of the pairwise potential is likely to be more relevant than the consideration of other forces.     

A photographic map of Drosophila hydei polytene chromosomes

A photographic map of polytene chromosomes of Drosophila hydei has been constructed after applying microdissection techniques.