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R J Wyman

Publications and source records attributed to R J Wyman.

At least 19 recordsLinked to original sources
PubMed1996

Passover eliminates gap junctional communication between neurons of the giant fiber system in Drosophila. off.

The Passover-related gene family plays significant roles in cellular connectivity. Mutations in three family members from Drosophila and from Caenorhabditis elegans alter a few specific electrical synapses. The passage of cobalt between Drosophila neurons was used to assay the presence of gap junctional connections. The giant fiber in the wild type has specific gap junctional connections in the brain and in the thorax. In flies mutant for Passover, cobalt cannot pass into or out of the giant fiber in either the anterograde or the retrograde directions. A large number of other gap junctional connections remain unaffected. This demonstrates that the Passover gene is necessary for gap-junctional communication between the neurons of the Drosophila giant fiber system.

Alleles↗
PubMed1995

Molecular basis of intracistronic complementation in the Passover locus of Drosophila.

The only demonstrated mechanism for intracistronic genetic complementation requires physical interaction of protein subunits to create a functional molecule. We demonstrate another and perhaps quite general mechanism utilizing proteins with unique and shared domains. The Drosophila neural mutant Passover (Pas) disrupts specific synaptic connections. Alleles of a lethal complementation group exhibit a complex pattern of complementation with Pas alleles. Whereas all heterozygotes between these lethal alleles and Pas are viable, only some alleles complement the neural defect of Pas. Lethal and neural functions are separately encoded by two proteins that have distinct N-terminal domains and a common C-terminal portion. Neural-specific and lethal-specific mutations map to unique exons, while neural-lethal mutations map to shared exons. Combinations of lethal and neural alleles result in production of both proteins and demonstrate intracistronic complementation.

Alleles↗
PubMed1993

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.

Alleles↗
PubMed1993

Dendritic reduction in Passover, a Drosophila mutant with a defective giant fiber neuronal pathway.

The jump response to a light-off startle stimulus in Drosophila melanogaster occurs when the Giant Fiber (GF), a neuron descending from the brain to the thorax, drives the jump (tergotrochanteral) muscle motorneuron (TTMn). Nonjumping mutants have been isolated in which this response is disrupted. Flies bearing the X-chromosome mutation Passover (Pas) fail to jump in response to a light-off stimulus, and electrical stimulation of the GF in the brain no longer elicits the normal response in the TTM. We have used retrograde HRP labelling to examine the TTMn motorneuron in wild-type flies and in a variety of newly identified Pas alleles. In wild type the medial branch (MB) of the TTMn has an extensive region of apposition with the GF. In Pas alleles, there is a general reduction in anterior-posterior (A-P) extent of the medial branch but not of the posterior branch. Nevertheless, Pas alleles usually leave the TTMn close enough to the GF so that contact would not be precluded. In flies carrying a particular deficiency of Pas, Df(1) 16-3-22, including Pas/Df(1) 16-3-22 heterozygotes, there can be extensive growth of the medial-branch including a contralateral projection; these heterozygotes have more than the normal amount of overlap between the GF and the TTMn. This phenotype, originally ascribed to Pas mutants, is associated with Df(1) 16-3-22, but not with other deletions of the Pas gene. The driving of the TTMn by the GF is defective in mutant genotypes with extensive medial branches as well as in mutants where GF-TTMn contact is reduced. The fact that the TTMn grows into its normal synaptic region in mutant genotypes, but the GF pathway functions abnormally suggests that pathfinding by the TTMn is not impaired. It is more likely that the Pas mutation disrupts cell recognition, synaptogenesis, or synaptic function in the TTMn or its presynaptic partners.

Animals↗
PubMed1993

Reevaluation of electrophoresis in the Drosophila egg chamber.

To evaluate the hypothesis of electrophoretic transport of cytoplasmic components, the transfollicle potentials of Drosophila oocytes and nurse cells were measured using improved techniques. We found input resistances 20 to 1000 times higher than those in previous reports. Measurements were made in a large variety of conditions: in external potassium concentrations from 1 to 100 mM, over the concomitant membrane potential range -84 to -23 mV, from developmental stages 5 to 10, and with or without using hemolymph, anesthetics, or collagenase. In all of these circumstances, no voltage gradient was detectable with intracellular microelectrodes from nurse cells to oocyte or between nurse cells. No voltage gradient was detected with external suction electrodes. Our results do not support the electrophoretic theory.

Animals↗
PubMed1993

Duplication of the escape-response neural pathway by mutation of the bithorax-complex.

Each Drosophila segment exhibits specific patterns of epidermal cells, muscles, and neurons. Mutations in the homeotic genes of the bithorax-complex cause transformations of these patterns. Whereas abundant information exists concerning homeotic transformation of epidermis, transformations of muscles and motor neurons have been largely unexplored. An important indication of neuromuscular transformation in a segment is the expression of novel behavioral and physiological functions within that segment. We have resolved some of the segmental identities of neuromuscular elements in the transformed metathorax of the bithorax-complex mutant, abx bx3 pbx/Df(3R) P2, and have established the presence of a duplicated neural pathway for the escape-jump response within that segment. Although we observed frequent homeotic transformation of neural elements and the tergotrochanteral ("jump") muscle in mutants, corresponding transformation of flight muscles was infrequent, indicating that the presence of a motor neuron was not always sufficient to induce or determine the development of its target muscle.

Animals↗
PubMed1990

A deficiency chromosome in Drosophila alters neuritic projections in an identified motoneuron.

The tergotrochanteral muscles (TTM) in the second thoracic segment of the fruitfly, Drosophila melanogaster, power the jump-escape response. The cell bodies of the motoneurons innervating these muscles, located in the thoracico-abdominal ganglion, have prominent posterior and medial neurites. While in wildtype flies of the Canton-S (C-S) and Oregon-R (O-R) strains, the medial neurite of a TTM motoneuron rarely crossed the midline (C-S: 0/17; O-R: 2/8), in heterozygous flies with a deficiency at the base of the X-chromosome, Df(1)16-3-22, the medial neurite frequently crossed the midline (Df(1)16-3-22/C-S: 7/12; Df(1)16-3-22/O-R: 18/22).

Animals↗
PubMed1990

Morphometric analysis of thoracic muscles in wildtype and in bithorax Drosophila.

The tergotrochanteral (TTM) "jump" muscles in the second (T2) and third (T3) thoracic segments of the fruit fly, Drosophila melanogaster, were analyzed morphologically and morphometrically in wildtype (Canton-S) and bithorax mutants (abx bx3 pbx/Df(3R)P2). In the transformed T3 segments of mutant flies, the TTMs were greatly increased in fiber number (330% of wildtype), length (141%), and volume (460%), thus manifesting both hyperplasia and hypertrophy. In contrast, TTMs in the "untransformed" T2 segments of mutant flies were both hypoplastic and hypotrophic, in that significant decreases in fiber number (93% of wildtype), length (90%), and volume (80%) were observed. Two relationships emerged from analysis of the morphometric data: 1) Although the fiber numbers and volumes of the transformed T3 TTMs in bithorax flies were greatly increased, the total combined volumes of the TTMs in T2 + T3 remained approximately the same in bithorax compared to wildtype flies. 2) The changes in TTM volumes in bithorax flies compared to those in wildtype were proportional to the relative changes in fiber numbers times the relative changes in muscle lengths. These observations suggest that the genes of the bithorax complex influence the number and the length of tubular muscles fibers of the TTMs, but do not significantly affect the mean cross-sectional areas of these fibers. Fibrillar muscle fibers, which are not found at all in T3 segments in wildtype flies, were observed in the transformed T3 segments of bithorax mutants in 11 of 18 cases (61%), but typically as wisps, not in complete muscles. We suggest that, in the T3 segment of the bithorax flies, the relative differences between the massive transformation of tubular TTMs vs. the minimal appearance of fibrillar muscles may be related, in part, to the relative availability of muscle precursors.

Animals↗
PubMed1990

Examination of paralysis in Drosophila temperature-sensitive paralytic mutations affecting sodium channels; a proposed mechanism of paralysis.

We have used the identified cells of the Drosophila Giant Fiber System (GFS) to study the defects induced by the temperature-sensitive paralytic mutations no action potential (nap) and paralytic (para). These mutations paralyze at elevated temperatures, reported as due to a block of action potential propagation. We found, however, that the cells of the GFS still were able to respond to stimuli at 7-10 degrees C above the temperature causing mutant paralysis. Stimulus threshold and conduction time both decrease with increasing temperature in the mutants in a manner indistinguishable from wild-type. Since action potentials can propagate efficiently in the mutants at elevated temperatures, we looked for other neural defects that might be involved in producing paralysis. We did find reduced neuronal function at sites such as electrical synapses and axonal branch points where current may be limiting. These sites had weakened following frequency, occasional failures, and increased conduction times. We believe the non-temperature-dependent defects in nap and para uncover the normally temperature-sensitive traits latent within all neurons. Increasing temperature increases the rates of channel activation and inactivation. At higher temperatures, Na+ inactivation and K+ activation encroach upon the Na(+)-activation time, reducing inward sodium current. In addition to this normal temperature-dependent effect, the mutations decrease the number of sodium channels in neurons in a non-temperature-dependent manner. These two reductions in sodium current combine to prevent spiking threshold from being reached at current limited sites. The temperature at which a sufficient number of these sites block should be the temperature of paralysis.

Action Potentials↗
PubMed1990

The Passover locus in Drosophila melanogaster: complex complementation and different effects on the giant fiber neural pathway.

Drosophila melanogaster bearing the Passover mutation fail to jump in response to a light-off stimulus. Pas also disrupts some of the synapses between the neurons of the giant fiber system which mediate this escape behavior. We have mapped Pas to the 19E subdivision of the polytene X chromosome. Our genetic analyses reveal that deletions of either of two nonoverlapping regions fail to fully complement Pas. Heterozygotes of Pas with chromosomal deletions in the vicinity of polytene band 19E3 exhibit the full set of neuronal defects shown by Pas homozygotes. Alleles of the R-9-29 complementation group, which maps to band 19E3, exhibit a complex pattern of complementation with Pas. Heterozygotes combining the lethal R-9-29 alleles with Pas are all viable, some complement the neuronal defects of Pas, but most exhibit these defects. The viable shaking-B2 mutation also fails to complement Pas, the R-9-29 alleles or the 19E3 deficiencies. The R-9-29 locus may contain two functional domains, one required for viability the other for normal neuronal phenotype, trans-Heterozygotes bearing mutant alleles or a deficiency of the first region (19E3) together with deficiencies of the second region (19E5-6) also exhibit some of the neuronal defects shown by the Passover mutant. Deficiencies which delete the entire 19E3 to 19E6 interval do not produce this phenotype when heterozygous with a normal X chromosome. Thus normal function requires a cis-interaction between the two regions. These findings raise the possibility that the gene mutated by Pas is split or separated from a cis-activator by at least one other gene.

Alleles↗
PubMed1986

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.

Animals↗
PubMed1984

Duplicated neural structure in bithorax mutant Drosophila.

The bithorax complex (BX-C) of genes in Drosophila control the segmental identity of the thoracic and abdominal cuticle. In flies containing BX-C mutations causing meta- to mesothoracic transformation, the mesothoracic branching pattern of a well-studied identified neuron is faithfully duplicated in the metathoracic ganglion. Thus these mutations also cause the duplication of mesothoracic cues involved in this neuron's branching.

Abdomen↗
PubMed1984

Mutations altering synaptic connectivity between identified neurons in Drosophila.

By studying the effects of mutations on a simple circuit of identified neurons in Drosophila, we have found genes whose proper functioning is necessary to produce normal synaptic connections between the neurons. These neurons comprise the giant fiber (GF) system; the GFs are command neurons activated by a light-off stimulus and evoke a stereotyped pattern of activity in the thoracic muscles producing an escape jump. Each GF monosynaptically drives a motor neuron innervating the tergotrochanteral muscle (jump muscle, TTM). Each GF also disynaptically drives the motor neurons innervating the dorsal longitudinal flight muscle (DLM) via the peripherally synapsing interneuron (PSI) (King, D. G., and R. J. Wyman (1980) J. Neurocytol. 9: 753-770; M. A. Tanouye and R. J. Wyman (1980) J. Neurophysiol. 44: 405-421). A search was made for mutations affecting these identified synapses. Fifty thousand mutagenized flies were screened for nonjumping behavior to the light-off stimulus. Fifty-seven nonjumping mutant lines were established from individuals selected in the screen. Members of the lines were then tested for abnormal GF motor output to the TTM and DLM. From these lines, four X-linked mutations (representing three complementation groups) were isolated which affect the circuit. The mutations differentially disrupt specific synapses within the GF system. One mutation, bendless, disrupts synaptic transmission between the GF and the TTM motor neuron. Another, gfA, disrupts the synaptic connections of the PSI, and a third mutation, passover, disrupts transmission in both pathways.

Animals↗
PubMed1983

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.2. The fast transient potassium current (I(A)) is the first channel to appear in the developing muscle membrane. It can be studied in isolation between 60 and 70 hr of pupal development. The channels can be observed to carry both outward and inward currents depending on the external potassium concentration. I(A) is blocked by both tetraethylammonium ion (TEA) and 3- or 4-aminopyridine. The inactivation and recovery properties of I(A) are responsible for a facilitating effect on membrane excitability.3. The delayed outward current (I(K)) develops after maturation of the I(A) system. I(K) can be isolated from I(A) by use of a mutation that removes I(A) from the membrane current response and can be studied before the development of Ca(2+) channels. I(K) shows no inactivation. The channels are more sensitive to blockage by TEA than I(A) channels, but are not substantially blocked by 3- or 4-aminopyridine.4. The calcium current (I(Ca)) is the last of the major currents to develop and must be isolated pharmacologically with potassium-blocking agents. I(Ca) shows inactivation when Ca(2+) is present but not when Ba(2+) is the sole current carrier. When Ca(2+) is the current carrier, the addition of Na(+) or Li(+) retards the inactivation of the net inward current. When the membrane voltage is not clamped, Ba(2+) alone, or Ca(2+) with Na(+) (or Li(+)), produces a plateau response of extended duration.5. The synaptic current (I(J)) evoked by motoneurone stimulation is the fastest and largest of the current systems. It has a reversal potential of approximately -5 mV, indicating roughly equal permeabilities of Na(+) and K(+). During a nerve-driven muscle spike, I(J) is the major inward current, causing a very rapid depolarization away from resting potential. An exceptionally large synaptic current is necessary to rapidly discharge the high membrane capacitance (0.03 muF/cell) in these large (0.05 x 0.1 x 0.8 mm) isopotential cells.

Aminopyridines↗
PubMed1982

The mathematics of mosaic analysis. I: The relationship between sturts and distance.

In mosaic fate mapping the fraction of mosaics in which two structures are of different genotype is calculated. This frequency of separation has been called a "distance" and the units of this distance are called "sturts". The fundamental assumption of fate mapping is that the frequency of separation increases continuously with the actual distance between the anlage for these structures on the blastoderm. This paper shows that the frequency of separation does not increase beyond a certain value. --For the current theory to work as proposed, each mosaic animal must be half mutant and half normal. This is rarely the case in collections of mosaics. It has been thought that if some flies are less than half mutant and others more than half, these two types would introduce compensating errors in mapping distance. We show that this is not true and describe the nature of the errors introduced. It is probable that these errors are the main reason that mapping distances reported from different sets of mosaics have not been reproducible. This paper presents methods for the proper handling of data from mosaics with different amounts of mutant tissue.--We prove here that for mosaics with an arbitrary fraction of mutant tissue (m), the largest frequency of separation that can occur is 2m. We prove that sturts underestimate actual distance on the blastoderm by a factor of r/m, where r is the radius of the mutant patch, and that sturts give no information on distances greater than 2r. This, and not double crossing over, is the reason for the nonadditivity of sturts and the shrinking of large distances in sturt measures. Sturtoids overestimate distances by a factor of 1/(2r) and also give no information on distances over 2r. This paper gives formulae for correctly estimating distance when using a collection of mosaics with varying amounts of mutant tissue. We also describe the nature of the errors introduced by convoluted or elongate mosaic boundaries and by multiple mosaic patches.

Animals↗