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Biomedical subjects

L Y Jan

Publications and source records attributed to L Y Jan.

At least 199 records · Page 11Linked to original sources
PubMed1988

A protein component of Drosophila polar granules is encoded by vasa and has extensive sequence similarity to ATP-dependent helicases.

Determinants of pole cells, which are precursors of the germ line, are provided maternally and are localized to the posterior pole of the Drosophila egg, as are polar granules. It has been hypothesized that certain RNA molecules associated with polar granules may be necessary for pole cell determination. Using a monoclonal antibody (Mab46F11) against polar granules, we have cloned the gene for one of their components. This gene turns out to be vasa, which is required maternally for the formation of polar granules and germ cells. This polar granule component shows significant sequence similarity to eIF-4A, a translation initiation factor that binds to mRNA, and to other helicases.

Adenosine Triphosphate↗
PubMed1988

Cloning of a probable potassium channel gene from mouse brain.

Potassium channels comprise a diverse class of ion channels important for neuronal excitability and plasticity. The recent cloning of the Shaker locus from Drosophila melanogaster has provided a starting point for molecular studies of potassium channels. Predicted Shaker proteins appear to be integral membrane proteins and have a sequence similar to the sequence of the S4 segment of the vertebrate sodium channel, where the S4 segment has been proposed to be the voltage sensor. Expression studies in frog oocytes confirm that Shaker encodes a component of a potassium channel (the A channel) that conducts a fast transient potassium current. Here we report the isolation of complementary DNA clones from the mouse brain, the nucleotide sequences of which predict a protein remarkably similar to the Shaker protein. The strong conservation of the predicted protein sequence in flies and mammals suggests that these mouse clones encode a potassium channel component and that the conserved amino acids may be essential to some aspect of potassium channel function.

Amino Acid Sequence↗
PubMed1988

Expression of functional potassium channels from Shaker cDNA in Xenopus oocytes.

The Shaker gene of Drosophila melanogaster encodes a potassium-selective ion channel, the 'A' channel, or one of its subunits. A single Shaker messenger RNA species suffices to direct the synthesis of functional A channels in Xenopus oocytes. Physiological characteristics of the A currents induced by two different mRNA species are compared.

Animals↗
PubMed1988

Four cDNA clones from the Shaker locus of Drosophila induce kinetically distinct A-type potassium currents in Xenopus oocytes.

The Shaker gene encodes the A-channel of larval and pupal muscle, or one or more of its subunits. Alternative splicing produces messages for several different proteins; two mRNA species have previously been shown to induce the expression of A-currents in Xenopus oocytes. Two additional mRNAs have now been tested and found to produce A-currents in oocytes. The four currents differ in kinetics of inactivation, indicating that the Shaker products may contribute to kinetic diversity in A-channels of the fly and that sequences in both the amino- and carboxy-terminal regions are important for inactivation.

Animals↗
PubMed1988

The maternal sex determination gene daughterless has zygotic activity necessary for the formation of peripheral neurons in Drosophila.

The daughterless (da) gene is known to have separate maternal and zygotic functions: Maternally supplied daughterless activity is required for proper sex determination and dosage compensation in female embryos, whereas loss of zygotically supplied da+ activity causes embryonic lethality in both male and female embryos. We have found that the zygotic da+ activity is necessary for neural development: The use of neuron-specific antibodies and beta-galactosidase-marked X chromosomes has revealed that in both male and female embryos deletions or strong mutations of the da gene remove all peripheral neurons and associated sensory structures without disrupting the epithelium from which they derive. Partial da+ function causes partial removal of peripheral neurons. Our results indicate that da+ is required for the formation of peripheral neurons and their associated sensory structures.

Animals↗
PubMed1988

Identification of a component of Drosophila polar granules.

Information necessary for the formation of pole cells, precursors of the germ line, is provided maternally and localized to the posterior pole of the Drosophila egg. The maternal origin and posterior localization of polar granules suggest that they may be associated with pole cell determinants. We have generated an antibody (Mab46F11) against polar granules. In oocytes and early embryos, the Mab46F11 antigen is sharply localized to the posterior embryonic pole. In pole cells, it becomes associated with nuclear bodies within, and nuage around, the nucleus. Immunoreactivity remains associated with cells of the germ line throughout the life cycle of both males and females. This antibody recognizes a 72-74 X 10(3) Mr protein and is useful both as a pole lineage marker and in biochemical studies of polar granules.

Animals↗
PubMed1987

The tko locus, site of a behavioral mutation in D. melanogaster, codes for a protein homologous to prokaryotic ribosomal protein S12.

The tko (technical knockout) mutation is one of a family of behavioral mutations that cause "bang sensitivity" in D. melanogaster. Using P-element-mediated transformation, we show that a 3.1 kb piece of genomic DNA complements tko. This fragment contains only one complete transcript, 0.68 kb in length. This transcript is abundantly expressed through all stages of the life cycle, and we have isolated cDNAs corresponding to this transcript. Their sequence implies a protein product composed of 140 amino acids, which exhibits considerable sequence similarity to ribosomal protein S12 from both Euglena gracilis chloroplasts and E. coli. We suggest that tko codes for a mitochondrial ribosomal protein and that the tko phenotype results from defective mitochondria.

Amino Acid Sequence↗
PubMed1987

Transformation of sensory organs by mutations of the cut locus of D. melanogaster.

The identities of two types of sensory organs in the body wall of Drosophila, namely the external sensory organs and the chordotonal organs, are under genetic control. Embryonic lethal mutations in the cut gene complex transform the external sensory organs into chordotonal organs. The neurons, as well as the support cells forming the external sensory structures, change their morphological and antigenic characteristics to those of chordotonal organs, providing genetic evidence that these two types of sensory organs are homologous. Similar transformations of external sensory organs are observed in adult mosaic flies. Analysis of mosaic larvae and flies suggests that the cut gene function is required either in or near external sensory organs in order for them to acquire their correct identity.

Animals↗
PubMed1987

Cloning of genomic and complementary DNA from Shaker, a putative potassium channel gene from Drosophila.

On the basis of electrophysiological analysis of Shaker mutants, the Shaker locus of Drosophila melanogaster has been proposed to encode a structural component of a voltage-dependent potassium channel, the A channel. Unlike sodium channels, acetylcholine receptors, and calcium channels, K+ channels have not been purified biochemically. To facilitate biochemical studies of a K+ channel, genomic DNA from the Shaker locus has been cloned. Rearrangements in five Shaker mutants have been mapped to a 60-kilobase segment of the genome. Four complementary DNA clones have been analyzed. These clones indicate that the Shaker gene contains multiple exons distributed over at least 65 kilobases of genomic DNA in the region where the mutations mapped. Furthermore, the gene may produce several classes of alternatively spliced transcripts. Two of the complementary DNA clones have been sequenced and their sequences support the hypothesis that Shaker encodes a component of a K+ channel.

Animals↗
PubMed1987

Sequence of a probable potassium channel component encoded at Shaker locus of Drosophila.

Potassium currents are crucial for the repolarization of electrically excitable membranes, a role that makes potassium channels a target for physiological modifications that alter synaptic efficacy. The Shaker locus of Drosophila is thought to encode a K+ channel. The sequence of two complementary DNA clones from the Shaker locus is reported here. The sequence predicts an integral membrane protein of 70,200 daltons containing seven potential membrane-spanning sequences. In addition, the predicted protein is homologous to the vertebrate sodium channel in a region previously proposed to be involved in the voltage-dependent activation of the Na+ channel. These results support the hypothesis that Shaker encodes a structural component of a voltage-dependent K+ channel and suggest a conserved mechanism for voltage activation.

Animals↗
PubMed1987

Identification and purification of an irreversible presynaptic neurotoxin from the venom of the spider Hololena curta.

A search for potent toxins that inhibit neuronal calcium channels in Drosophila melanogaster has resulted in the identification of a presynaptic neurotoxin from the venom of the hunting spider Hololena curta. Using Drosophila neuromuscular junction as an assay, presynaptic inhibitory activity was purified using gel filtration and reverse-phase HPLC. Data from gel electrophoresis indicate that the toxin is composed of two different subunits of Mr 7000 and 9000. At nanomolar concentrations the toxin produced a complete and long-lasting inhibition of synaptic transmission at the Drosophila larval neuromuscular junction without affecting the amplitudes of the spontaneously occurring miniature junction potentials. The block of transmission produced by the toxin was observed even during the direct depolarization of the motor nerve terminal. These physiological results indicate that the terminal is the site of action for the toxin. Indirect evidence using abnormally excitable Drosophila mutants suggests that the toxin is inhibiting transmitter release by altering the electrical properties of the nerve terminal rather than by interfering with nonelectrical events that may occur subsequent to calcium influx. All of the actions of the Hololena toxin can be explained by a specific and direct effect on presynaptic calcium channels in Drosophila motor neurons.

Animals↗
PubMed1987

Gene dosage and complementation analysis of the Shaker locus in Drosophila.

Mutations of the Shaker (Sh) locus alter or eliminate a transient, voltage-sensitive potassium current, the "A" current, in flight muscle of Drosophila. We show that the amplitude of the A current is reduced when the dosage of Sh+ is lower than normal, but that A current amplitude does not increase as extra copies of Sh+ are added. We have also examined 14 Shaker mutants by voltage clamp and by intracellular recording at the larval neuromuscular junction. In 10 of these mutants there is no detectable fast component of the transient outward current. In each of these 10, however, a small, slowly inactivating, outward current is present. The 10 mutations null for the fast component of the transient, outward current are all partially dominant, giving 50-80% of the normal A current in Shnull/Sh+ heterozygotes. Because as little as 5% of the normal A current can be detected, complementation tests are feasible. The 10 null mutations are members of a single complementation group. The remaining 4 mutations have reduced A currents in pupal flight muscle. In all cases, crosses between these leaky mutants and null mutants give progeny with less A current than found in the leaky parental lines, as would be expected if the leaky and null mutations are in the same complementation group. For 1 of the mutations, ShrKO120, the mutant phenotype is much more severe in nerve than in muscle. That part of the Shaker locus required for the production of the A channel lies between the B55 and the V7 translocation breakpoints, in region 16F of the X chromosome.

Animals↗
PubMed1987

Neurotoxins from Plectreurys spider venom are potent presynaptic blockers in Drosophila.

Studies of presynaptic events in synaptic transmission may be facilitated through the use of specific ligands for functional components of the transmitter release mechanism and through the use of genetics. For this purpose, neurotoxins that affect neuromuscular transmission in Drosophila have been identified and purified from Plectreurys spider venom (PLTX). One class of toxins causes irreversible presynaptic block, probably by blocking calcium entry or by acting on other closely associated processes. These toxins have been highly purified and are peptides of about 7 kDa in molecular weight. They specifically block transmitter release at nanomolar concentrations and may be useful in further biochemical studies.

Animals↗
PubMed1986

Muscle connections between imaginal discs in Drosophila.

A comparison of the protein content of different imaginal discs of Drosophila revealed that among more than 600 protein species that can be detected, only three show differences in concentration among different types of discs. Two of them form a doublet that can be resolved only by using extended electrophoresis conditions. This doublet was also reported to have a nonhomogeneous distribution within some discs. Here we show that these two proteins are tropomyosin components, and that they are associated not with the discs themselves but with a new type of muscle that connects some of the discs together.

Antibodies, Monoclonal↗
PubMed1986

A substance P-like peptide in bullfrog autonomic nerve terminals: anatomy biochemistry and physiology.

Substance P immunoreactivity was localized to dense-cored vesicles in parasympathetic preganglionic nerve terminals in the bullfrog cardiac ganglion. Analysis with radioimmunoassay and high pressure liquid chromatography indicated that the immunoreactive substance was more similar to substance P than to substance K but was not identical to either. The bullfrog substance P was also shown to be different than kassinin, eledoisin, ranatensin, bombesin, neuromedin K and physalaemin. Although the peptide was present in most of the terminals in the ganglion and appeared to be releasable in a calcium-dependent manner, intracellular recordings from ganglion neurons during stimulation revealed no electrophysiological events that might be mediated by an endogenous peptide. In addition, the direct application of substance P to ganglion neurons generally produced no changes in membrane potential, membrane conductance, somal calcium spikes or nerve-evoked release of acetylcholine. High concentrations of substance P did cause an apparent increase in the rate of desensitization of the nicotinic receptors but there was little indication that this phenomenon would occur under physiological conditions. It is suggested that bullfrog substance P is released as a neurotransmitter but is involved in electrically silent events in the postsynaptic neurons or is acting on non-neuronal cells near the terminals. The possible implications of these results for peptidergic systems in general are discussed.

Animals↗