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R J Wyman

Publications and source records attributed to R J Wyman.

At least 19 recordsLinked to original sources
PubMed1999

Nested transcripts of gap junction gene have distinct expression patterns.

The shaking B locus (shakB, or Passover) codes for structural molecules of gap junctions in Drosophila. This report describes the complex set of transcripts from the shakB locus. A nested set of five transcripts is described. The transcripts share 3' exons, but each has its own 5' exon. The transcripts are arrayed as a series in the genomic DNA stretching over 60 kb. The 5' end of each successive transcript lies further proximal on the chromosome. Each new transcript shares all the 3' exons with the one preceding it, but adds one or two more 5' exons. The different transcripts are expressed in a wide variety of locations in the nervous system and in non-neural tissues. Some tissues express more than one transcript, and the expression pattern of each is developmentally regulated. Within the adult central nervous system (CNS), these transcripts have an expression pattern that is restricted to the giant fiber system (GFS). The GFS is a small set of neurons which mediates the visually induced escape jump. shakB is required for function of the GFS electrical synapses. The transcript previously defined as active in the giant fiber is not, in fact, expressed in that cell. Instead, we find that another transcript, shakB(N3), and perhaps shakB(N4) as well, is expressed in the GFS; this transcript is not expressed elsewhere in the adult CNS. Two other transcripts, shakB(N1) and shakB(N2), are expressed in the optic lamina but not elsewhere in the CNS. This expression pattern explains the neurophysiological and behavioral defects in escape exhibited in mutants of shakB.

Alternative Splicing↗
PubMed1999

Drosophila has several genes for gap junction proteins.

The Innexin gene family forms gap junctions in invertebrates. Many genes in this family have been identified in Caenorhabditis elegans, but only two in Drosophila. We have used PCR techniques to identify three new members of this family from Drosophila. These are designated pas-related proteins (prp) 6, 7, and 33. The putative proteins coded by these new genes show 25-35% identity and 39-66% similarity to other Drosophila innexins and share a similar hydrophobicity profile. The genes form two small clusters on the X-chromosome, with three of the genes sitting within 10kb of each other. The closeness in sequence and location suggests an evolutionary origin of these genes via local duplication. In situ hybridization shows expression in the CNS, gut and epidermis. Each gene has a distinct pattern of expression in different tissues at different developmental times. However, parts of the expression patterns overlap, especially for prp33 and ogre which may be expressed from the same transcriptional enhancers. This suggest that the Prp33 and Ogre proteins may join in forming heteromeric gap junction channels.

Amino Acid Sequence↗
PubMed1997

Patterns of connectivity in a Drosophila nerve.

We investigated the spatial patterns of synaptic profiles in en passant synapses between the premotor axon of a peripherally synapsing interneuron (PAPSI) and a set of individually identifiable motoneuron axons in Drosophila melanogaster. These synaptic profiles are distributed as the axons travel parallel to each other in a bundle; the synapses begin as the axons leave the thoracic ganglion and continue peripherally for 45-65 microm. We found that the number of synaptic profiles per micron length of the motoneuron axons was greatest close to the ganglion; the cumulative distribution of profiles could be fitted to curves of the form f(x) = alpha(1 - e(-beta x)), where x = the distance from the thoracic ganglion, and alpha and beta are constants. The distribution of synaptic profiles was also examined in a mutant strain, Passover (Pas), known to affect connectivity in a pathway that includes the PAPSI. The synaptic profiles between the PAPSI and the motoneuron axons appeared ultrastructurally unremarkable in Pas. Also, the total number of synaptic profiles between the PAPSI and the motoneuron axons did not differ between Pas and wild type flies. However, the distribution of synaptic profiles among the individual motoneuron axons did differ significantly from wild type flies, as did the area of contiguity between the motoneuron axons and the PAPSI, which was much greater in Pas than in wild type flies.

Animals↗
PubMed1997

Neurons of the Drosophila giant fiber system: I. Dorsal longitudinal motor neurons.

The giant fiber system (GFS) mediates the startle response of Drosophila. This response includes an activation of the dorsal longitudinal wing-depressor muscles (DLMs). However, the morphology of the motor neurons innervating these muscles has not been well studied. Even the location of the somata of these motor neurons has been a source of controversy. This paper identifies the somata and provides a morphological description of these motoneurons. The DLM is comprised of six muscle fibers, named a through f (dorsal to ventral). Each muscle fiber is singly innervated. Each of the four ventral muscle fibers is innervated by a separate motor neuron (DLMn c-f), but the two dorsal fibers share an axon (DLMn a/b). Motor neurons were back filled by introducing horseradish peroxidase (HRP) into individual muscle fibers. The cell body of DLMn a/b is extraordinarily large (32 microm) and lies dorsal and contralateral. In this hemiganglion, it does not have a fixed position; it can be found anywhere from the midline to the extreme lateral edge of the ganglion. The position is not genetically controlled: We find no strain differences, and, within a single individual, the right and left cells may take different positions. The neuritic arborization fills a shallow dorsal cap of the ganglion, with branches arrayed like a feather. The cell bodies of the four motor neurons c-f lie in an ipsilateral and ventral cluster. Each soma occupies a fixed corner of this quadrilaterally shaped cluster. The neurites ramify in the same dorsal region as DLMn a/b.

Animals↗
PubMed1997

Genetic basis of tolerance to O2 deprivation in Drosophila melanogaster.

The ability to tolerate a low-O2 environment varies widely among species in the animal kingdom. Some animals, such as Drosophila melanogaster, can tolerate anoxia for prolonged periods without apparent tissue injury. To determine the genetic basis of the cellular responses to low O2, we performed a genetic screen in Drosophila to identify loci that are responsible for anoxia resistance. Four X-linked, anoxia-sensitive mutants belonging to three complementation groups were isolated after screening more than 10,000 mutagenized flies. The identified recessive and dominant mutations showed marked delay in recovery from O2 deprivation. In addition, electrophysiologic studies demonstrated that polysynaptic transmission in the central nervous system of the mutant flies was abnormally long during recovery from anoxia. These studies show that anoxic tolerance can be genetically dissected.

Adaptation, Physiological↗
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↗