Robert J. Wyman

Ion currents in Drosophila flight muscles

1. The dorsal longitudinal flight muscles of Drosophila melanogaster contain three voltage‐activated ion currents, two distinct potassium currents and a calcium current. The currents can be isolated from each other by exploiting the developmental properties of the system and genetic tools, as well as conventional pharmacology.

Behavioral and Electrophysiologic Responses of Drosophila melanogaster to Prolonged Periods of Anoxia.

Sensitivity to anoxia varies tremendously among phyla and species. Most mammals are exquisitely sensitive to low concentrations of inspired oxygen, while some fish, turtles and crustacea are very resistant. To determine the basis of anoxia tolerance, it would be useful to utilize a model system which can yield mechanistic answers. We studied the fruit fly, Drosophila melanogaster, to determine its anoxia resistance since this organism has been previously studied using a variety of approaches and has proven to be very useful in a number of areas of biology. Flies were exposed to anoxia for periods of 5-240 min, and, after 1-2 min in anoxia, Drosophila lost coordination, fell down, and became motionless. However, they tolerated a complete nitrogen atmosphere for up to 4 h following which they recovered. In addition, a nonlinear relation existed between time spent in anoxia and time to recovery. Extracellular recordings from flight muscles in response to giant fiber stimulation revealed complete recovery of muscle-evoked response, a response that was totally absent during anoxia. Mean O(2) consumption per gram of tissue was substantially reduced in low O(2) concentrations (20% of control). We conclude from these studies that: (1) Drosophila melanogaster is very resistant to anoxia and can be useful in the study of mechanisms of anoxia tolerance; and (2) the profound decline in metabolic rate during periods of low environmental O(2) levels contributes to the survival of Drosophila. Copyright 1997 Elsevier Science Ltd. All rights reserved

The Leucokinin Pathway and Its Neurons Regulate Meal Size in Drosophila

BACKGROUND Total food intake is a function of meal size and meal frequency, and adjustments to these parameters allow animals to maintain a stable energy balance in changing environmental conditions. The physiological mechanisms that regulate meal size have been studied in blowflies but have not been previously examined in Drosophila. RESULTS Here we show that mutations in the leucokinin neuropeptide (leuc) and leucokinin receptor (lkr) genes cause phenotypes in which Drosophila adults have an increase in meal size and a compensatory reduction in meal frequency. Because mutant flies take larger but fewer meals, their caloric intake is the same as that of wild-type flies. The expression patterns of the leuc and lkr genes identify small groups of brain neurons that regulate this behavior. Leuc-containing presynaptic terminals are found close to Lkr neurons in the brain and ventral ganglia, suggesting that they deliver Leuc peptide to these neurons. Lkr neurons innervate the foregut. Flies in which Leuc or Lkr neurons are ablated have defects identical to those of leucokinin pathway mutants. CONCLUSIONS Our data suggest that the increase in meal size in leuc and lkr mutants is due to a meal termination defect, perhaps arising from impaired communication of gut distension signals to the brain. Leucokinin and the leucokinin receptor are homologous to vertebrate tachykinin and its receptor, and injection of tachykinins reduces food consumption. Our results suggest that the roles of the tachykinin system in regulating food intake might be evolutionarily conserved between insects and vertebrates.

Passover: A gene required for synaptic connectivity in the giant fiber system of Drosophila

Passover (Pas) flies fail to jump in response to a light-off stimulus. The mutation disrupts specific synapses of the giant fibers (GFs), command neurons for this response. Pas was cloned from a P element-induced allele. The cDNA encodes a putative membrane protein of 361 amino acids. Null, hypomorphic, and dominant alleles were sequenced. In the adult central nervous system, and in the pupa during GF synapse formation, Pas is consistently expressed in the GF and in a large thoracic cell in the location of its postsynaptic targets. Pas establishes a new gene family. The Drosophila ogre protein, required for postembryonic neuroblast development, is 47% identical; the C. elegans Unc-7 protein, which when mutated alters the connectivity of a few neurons, is 33% identical.

Basigin (EMMPRIN/CD147) interacts with integrin to affect cellular architecture.

Basigin, an IgG family glycoprotein found on the surface of human metastatic tumors, stimulates fibroblasts to secrete matrix metalloproteases that remodel the extracellular matrix. Using Drosophila melanogaster we identify intracellular, matrix metalloprotease-independent, roles for basigin. Specifically, we found that basigin, interacting with integrin, is required for normal cell architecture in some cell types. Basigin promotes cytoskeletal rearrangements and the formation of lamellipodia in cultured insect cells. Loss of basigin from photoreceptors leads to misplaced nuclei, rough ER and mitochondria, as well as to swollen axon terminals. These changes in intracellular structure suggest cytoskeletal disruptions. These defects can be rescued by either fly or mouse basigin. Basigin and integrin colocalize to cultured cells and to the visual system. Basigin-mediated changes in the architecture of cultured cells require integrin binding activity. Basigin and integrin interact genetically to affect cell structure in the animal, possibly by forming complexes at cell contacts that help organize internal cell structure.

Obesity-Blocking Neurons in Drosophila

In mammals, fat store levels are communicated by leptin and insulin signaling to brain centers that regulate food intake and metabolism. By using transgenic manipulation of neural activity, we report the isolation of two distinct neuronal populations in flies that perform a similar function, the c673a-Gal4 and fruitless-Gal4 neurons. When either of these neuronal groups is silenced, fat store levels increase. This change is mediated through an increase in food intake and altered metabolism in c673a-Gal4-silenced flies, while silencing fruitless-Gal4 neurons alters only metabolism. Hyperactivation of either neuronal group causes depletion of fat stores by increasing metabolic rate and decreasing fatty acid synthesis. Altering the activities of these neurons causes changes in expression of genes known to regulate fat utilization. Our results show that the fly brain measures fat store levels and can induce changes in food intake and metabolism to maintain them within normal limits.

The morphology of the cervical giant fiber neuron ofDrosophila

The morphology of the cervical giant fiber (CGF) neuron of Drosophila melanogaster was studied by intracellular injection of Lucifer yellow dye. The CGF neuron is the command cell in a motor circuit causing visually driven escape behavior: a single action potential in a CGF axon produces patterned activity in jump and flight muscles. The present study identified the CGF cell body, a large soma located in the posterior part of the lower ipsilateral protocerebrum. The main process runs anteriorly from the cell body, extends three branches, and turns posteromedially while descending through the brain. The CGF axon courses through the cervical connective and ends within the mesothoracic neuromere of the thoracic ganglion. Thus, the CGF neuron is an interneuron, not a motoneuron as previously believed. We have been isolating mutants that affect CGF neuron-mediated behavior. Comparison of CGF neuron morphology in wildtype strains with that in these mutants will allow identification of genes that affect the development, structure, and connections of the CGF neuron.

The Drosophila Giant Fiber System

Normal functioning of the nervous system depends on the formation of vast numbers of specific connections between neurons. During development, each of the thousands, millions, or billions of cells in a nervous system connects with a specific set of target cells. We currently have no knowledge of the molecular basis of this specificity. The long-term goal of our work is to identify genes that are directly involved in neural connectivity and then to use this knowledge to identify the gene products necessary for proper connectivity. It will be a major advance in neuroscience if the class (or classes) of molecules involved in nerve-cell recognition and connection can be identified.

Development of an indirect flight muscle in a muscle-specific mutant of Drosophila melanogaster☆

Stripe (sr) is a highly specific mutant affecting only one of the indirect flight muscles, the dorsal longitudinal muscle (DLM). In the homozygous condition the DLM is reduced in size. In the hemizygous condition (sr/Df(3)sr) no DLM is present in the adult, though all other thoracic muscles are present. In the early stages of pupation, DLM development in sr/Df(3)sr is no different from that in wild type. Adult myocytes collect around target larval muscles and fuse to form myotubes; myofilaments are synthesized. Subsequently (35-hr pupa) the DLM commences to degenerate, forming random clumps of vacuolated muscle tissue. Adjacent muscles are unaffected and develop normally. In the adult a neuroma-like mass of nerve tissue is maintained where the DLM would normally be located. In this mass many abnormal synapses (hemisynapses) are seen: presynaptic specializations occur in the absence of any postsynaptic structure. Small remnants (less than 16-microns diameter) of muscle tissue are sometimes found in the neuroma-like mass. Such remnants resemble slow muscle, not the normal fast type of DLM. These data suggest a possible muscle origin from primary and secondary myotubes. The DLM motor axons are present in the neuroma-like mass, persisting even with the virtual degeneration of their end target. Thus, motoneurons and presynaptic specializations can survive independently of postsynaptic targets.

A reappraisal of reflex stepping in the cat

1. In re‐evaluating Sherringtons experiment in which deafferented muscles in decerebrated cats ‘stepped’, we recorded from L5 ventral roots, a chief supplier of the major extensors of the hind legs, during stimulation of the common peroneal nerves. The extensor muscles had been denervated by appropriate dorsal root sections; the cats had been paralysed with a neuromuscular blocking agent.