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.appetite ͉ feeding ͉ ingestion ͉ preference U nderstanding the physiology and regulation of appetite is an indispensable step in tackling biomedical problems such as obesity and feeding disorders. Invertebrate model systems have provided invaluable mechanistic insight into the genetic control of various biological and pathological processes, but have contributed relatively little to the understanding of the genetic underpinnings and neuronal circuitry of appetite regulation. This dearth is largely due to the limits of the available methodology. In both Caenorhabditis elegans and Drosophila melanogaster, feeding behavior is often inferred from qualitative parameters such as the amount of time spent on a given food source or the percentage of animals from a population seen eating or simply loitering on the medium at a given time (1-3). A more direct method, widely used in the nematode, is the pharyngeal pumping rate, which assumes a constant ingestion volume per pharyngeal contraction (4-6). In Drosophila, food can be labeled with nonabsorbable dyes (6, 7) or radioactive isotopes (8-12), but these techniques also have several limitations. Dyes progress rapidly through the digestive tract, precluding long-term measurements. Isotope labeling, on the other hand, permits longterm recordings but does not distinguish between ingestion and intestinal absorption, leading to permanent tissue incorporation. Most importantly, labeling methods require killing the flies for each measurement, making it impossible to continuously monitor the behavior of individual animals.We describe a method allowing unambiguous recording of food ingestion in individual or groups of flies on the scale of minutes to the entire lifespan. Monitoring ingestion at short, 10-min intervals permitted the delineation of single meals. By modulating nutrient composition, we show that the pa...

The TGF-␤ superfamily of growth and differentiation factors, including TGF-␤, Activins and bone morphogenetic proteins (BMPs) play critical roles in regulating the development of many organisms. These factors signal through a heteromeric complex of type I and II serine/threonine kinase receptors that phosphorylate members of the Smad family of transcription factors, thereby promoting their nuclear localization. Although components of TGF-␤/Activin signaling pathways are well defined in vertebrates, no such pathway has been clearly defined in invertebrates. In this study we describe the role of Baboon (Babo), a type I Activin receptor previously called Atr-I, in Drosophila development and characterize aspects of the Babo intracellular signal-transduction pathway. Genetic analysis of babo loss-of-function mutants and ectopic activation studies indicate that Babo signaling plays a role in regulating cell proliferation. In mammalian cells, activated Babo specifically stimulates Smad2-dependent pathways to induce TGF-␤/Activin-responsive promoters but not BMP-responsive elements. Furthermore, we identify a new Drosophila Smad, termed dSmad2, that is most closely related to vertebrate Smads 2 and 3. Activated Babo associates with dSmad2 but not Mad, phosphorylates the carboxy-terminal SSXS motif and induces heteromeric complex formation with Medea, the Drosophila Smad4 homolog. Our results define a novel Drosophila Activin/TGF-␤ pathway that is analogous to its vertebrate counterpart and show that this pathway functions to promote cellular growth with minimal effects on patterning.

We researched the lifespan of Drosophila under axenic conditions compared with customary procedure. The experiments revealed that the presence of bacteria during the first week of adult life can enhance lifespan, despite unchanged food intake. Later in life, the presence of bacteria can reduce lifespan. Certain long-lived mutants react in different ways, indicating an interplay between bacteria and longevity-enhancing genes.longevity ͉ aging ͉ axenic flies ͉ antibiotics