Seymour Benzer

Regulation of lifespan in Drosophila by modulation of genes in the TOR signaling pathway.

In many species, reducing nutrient intake without causing malnutrition extends lifespan. Like DR (dietary restriction), modulation of genes in the insulin-signaling pathway, known to alter nutrient sensing, has been shown to extend lifespan in various species. In Drosophila, the target of rapamycin (TOR) and the insulin pathways have emerged as major regulators of growth and size. Hence we examined the role of TOR pathway genes in regulating lifespan by using Drosophila. We show that inhibition of TOR signaling pathway by alteration of the expression of genes in this nutrient-sensing pathway, which is conserved from yeast to human, extends lifespan in a manner that may overlap with known effects of dietary restriction on longevity. In Drosophila, TSC1 and TSC2 (tuberous sclerosis complex genes 1 and 2) act together to inhibit TOR (target of rapamycin), which mediates a signaling pathway that couples amino acid availability to S6 kinase, translation initiation, and growth. We find that overexpression of dTsc1, dTsc2, or dominant-negative forms of dTOR or dS6K all cause lifespan extension. Modulation of expression in the fat is sufficient for the lifespan-extension effects. The lifespan extensions are dependent on nutritional condition, suggesting a possible link between the TOR pathway and dietary restriction.

Development of the Drosophila retina, a neurocrystalline lattice☆

Pattern formation in the Drosophila retina proceeds by the recruitment of cells, along a morphogenetic front, into a lattice. At the advancing front, marked by a dorso-ventral furrow in the eye imaginal disc, cells are organized into ommatidial precursors, each containing cells destined to become photoreceptors 2, 3, 4, 5, and 8. Behind the front, a mitotic wave produces photoreceptors 1, 6, and 7, plus the remaining cells needed to complete the ommatidia. During the third larval instar, the front sweeps anteriorly across the eye disc, leaving a highly ordered pattern in its wake. Preceding the dorso-ventral furrow is a groove that bisects the eye disc into dorsal and ventral halves and presumably plays a role in establishing the equatorial symmetry line. Cell lineage plays little role in pattern formation in the eye. Genetic mosaics show that the cells of each ommatidium are not derived from a single mother cell; the cells appear to be recruited at random at the morphogenetic front. Similarly, the mirror symmetry above and below the equator is not established by a clonal mechanism; a single clone can contribute cells to ommatidia on both sides of the equator.

painless, a Drosophila Gene Essential for Nociception

We describe a paradigm for nociception in Drosophila. In response to the touch of a probe heated above 38 degrees C, Drosophila larvae produce a stereotypical rolling behavior, unlike the response to an unheated probe. In a genetic screen for mutants defective in this noxious heat response, we identified the painless gene. Recordings from wild-type larval nerves identified neurons that initiated strong spiking above 38 degrees C, and this activity was absent in the painless mutant. The painless mRNA encodes a protein of the transient receptor potential ion channel family. Painless is required for both thermal and mechanical nociception, but not for sensing light touch. painless is expressed in peripheral neurons that extend multiple branched dendrites beneath the larval epidermis, similar to vertebrate pain receptors. An antibody to Painless binds to localized dendritic structures that we hypothesize are involved in nociceptive signaling.

The eyes absent gene : genetic control of cell survival and differentiation in the developing Drosophila eye

The eyes absent (eya) gene is required at an early stage in development of the D. melanogaster compound eye. In eya mutants, progenitor cells in the eye disc undergo programmed cell death anterior to the morphogenetic furrow, rather than proceeding into the pathway of retinal differentiation. A low level of cell death normally occurs at this stage, suggesting that eya activity influences the distribution of cells between differentiation and death. Molecular analysis identifies a nuclear protein expressed in progenitor cells prior to differentiation. Transformation with the cDNA prevents progenitor cell death and allows the events that generate the eye to proceed. eya activity is required for the survival of eye progenitor cells at a critical stage in morphogenesis.

A single population of olfactory sensory neurons mediates an innate avoidance behaviour in Drosophila

All animals exhibit innate behaviours in response to specific sensory stimuli that are likely to result from the activation of developmentally programmed neural circuits. Here we observe that Drosophila exhibit robust avoidance to odours released by stressed flies. Gas chromatography and mass spectrometry identifies one component of this ‘Drosophila stress odorant (dSO)’ as CO2. CO2 elicits avoidance behaviour, at levels as low as 0.1%. We used two-photon imaging with the Ca2+-sensitive fluorescent protein G-CaMP to map the primary sensory neurons governing avoidance to CO2. CO2 activates only a single glomerulus in the antennal lobe, the V glomerulus; moreover, this glomerulus is not activated by any of 26 other odorants tested. Inhibition of synaptic transmission in sensory neurons that innervate the V glomerulus, using a temperature-sensitive Shibire gene (Shits), blocks the avoidance response to CO2. Inhibition of synaptic release in the vast majority of other olfactory receptor neurons has no effect on this behaviour. These data demonstrate that the activation of a single population of sensory neurons innervating one glomerulus is responsible for an innate avoidance behaviour in Drosophila.

Neuronal development in the drosophila retina: Monoclonal antibodies as molecular probes

The compound eye of D. melanogaster is a reiterative pattern of facets, each containing eight photoreceptor cells in a precise arrangement. This pattern is established in the eye imaginal disc during the third larval instar. A wave of morphogenesis sweeps from posterior to anterior across the disc, leaving in its wake organized clusters of photoreceptor cells. We have used monoclonal antibodies to highlight pattern elements that are not readily observable by other techniques. Monoclonal antibodies can be used to identify the molecules associated with particular patterns, providing links between observable structures and the genes. As an example, we present the purification and N-terminal sequence of a glycoprotein antigen specific to photoreceptor cells and their axons.

Prandiology of Drosophila and the CAFE assay

Studies of feeding behavior in genetically tractable invertebrate model systems have been limited by the lack of proper methodology. We introduce the Capillary Feeder (CAFE), a method allowing precise, real-time measurement of ingestion by individual or grouped fruit flies on the scale of minutes to days. Using this technique, we conducted the first quantitative analysis of prandial behavior in Drosophila melanogaster. Our results allow the dissection of feeding into discrete bouts of ingestion, defining two separate parameters, meal volume and frequency, that can be uncoupled and thus are likely to be independently regulated. In addition, our long-term measurements show that flies can ingest as much as 1.7× their body mass over 24 h. Besides the study of appetite, the CAFE can be used to monitor oral drug delivery. As an illustration, we used the CAFE to test the effects of dietary supplementation with two compounds, paraquat and ethanol, on food ingestion and preference. Paraquat, a prooxidant widely used in stress tests, had a strong anorexigenic effect. In contrast, in a feeding preference assay, ethanol-laced food, but not ethanol by itself, acted as an attractant.

Life extension in Drosophila by feeding a drug

We report that feeding Drosophila throughout adulthood with 4-phenylbutyrate (PBA) can significantly increase lifespan, without diminution of locomotor vigor, resistance to stress, or reproductive ability. Treatment for a limited period, either early or late in adult life, is also effective. Flies fed PBA show a global increase in histone acetylation as well as a dramatically altered pattern of gene expression, including induction or repression of numerous genes. The delay in aging may result from the altered physiological state.

Rotation of photoreceptor clusters in the developing drosophila eye requires the nemo gene

The Drosophila eye consists of a reiterative hexagonal array of photoreceptor cell clusters, the ommatidia. During normal morphogenesis, the clusters in the dorsal or ventral halves of the disc rotate 90 degrees in opposite directions, forming mirror images across a dorsoventral equator. In the mutant nemo (nmo), there is an initial turning of approximately 45 degrees, but further rotation is blocked. Genetic mosaic analysis indicates that the nmo gene acts upon each cluster as a whole; normal nmo function in one or more photoreceptor cells appears to be sufficient to induce full rotation. The nmo gene sequence encodes a serine/threonine protein kinase homolog, suggesting that the kinase is required to initiate the second step of rotation. In another mutant, roulette, excessive rotation through varying angles occurs in many ommatidia. This defect is suppressed by nmo, indicating that nmo acts upstream in a rotation-regulating pathway.

Allocrine Modulation of Feeding Behavior by the Sex Peptide of Drosophila

Mating elicits a dramatic reprogramming of female behavior in numerous insect species. In Drosophila, this postmating response (PMR) comprises increased egg-laying rate and reduced sexual receptivity and is controlled by the products of the male accessory glands, a family of approximately 80 small peptides transferred in the male seminal fluid . Here, we show that copulation strongly stimulates female food intake. Remarkably, this change is abolished if the males lack a single, small seminal protein, the Sex Peptide (SP). Ectopic expression of SP in virgin females mimics the effect of mating on feeding behavior, demonstrating that SP is the main agent controlling this behavioral paradigm. Our observations identify enhanced feeding behavior as a novel component of the Drosophila PMR and suggest that SP represents a molecular link between energy acquisition and reproductive investment.