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D L Lewis

Publications and source records attributed to D L Lewis.

At least 19 recordsLinked to original sources
PubMed2000

Distinct roles of the homeotic genes Ubx and abd-A in beetle embryonic abdominal appendage development.

Insects are easily distinguishable by the absence of legs on the adult abdomen. Studies performed on the Dipteran, Drosophila melanogaster, indicate that this is because of the repressive effects of the homeotic genes Ultrabithorax (Ubx) and abdominal-A (abd-A) on the limb promoting gene Distal-less (Dll) during embryonic development. However, in many species appendage-like structures are present on abdominal segments in embryonic and juvenile stages. Here, by using classical genetics and double-stranded RNA-mediated gene silencing in the red flour beetle, Tribolium castaneum, a species that develops an appendage on the first abdominal segment, we investigate the roles of Ubx and Abd-A in abdominal limb development. We find that in Tribolium, Abd-A, but not Ubx, represses early expression of Dll in the embryonic abdomen. Ubx appears to modify the A1 appendage. This difference in the activities of Abd-A and Ubx is critical for proper development of this appendage. We suggest that an ancestral role of Abd-A in insect abdominal appendage development was in the repression of Dll initiation and that of Ubx was in modulation of abdominal appendage morphology.

Abdomen↗
PubMed1999

Ectopic gene expression and homeotic transformations in arthropods using recombinant Sindbis viruses.

BACKGROUND: The morphological diversity of arthropods makes them attractive subjects for studying the evolution of developmental mechanisms. Comparative analyses suggest that arthropod diversity has arisen largely as a result of changes in expression patterns of genes that control development. Direct analysis of how a particular gene functions in a given species during development is hindered by the lack of broadly applicable techniques for manipulating gene expression. RESULTS: We report that the Arbovirus Sindbis can be used to deliver high levels of gene expression in vivo in a number of non-host arthropod species without causing cytopathic effects in infected cells or impairing development. Using recombinant Sindbis virus, we investigated the function of the homeotic gene Ultrabithorax in the development of butterfly wings and beetle embryos. Ectopic Ultrabithorax expression in butterfly forewing imaginal discs was sufficient to cause the transformation of characteristic forewing properties in the adult, including scale morphology and pigmentation, to those of the hindwing. Expression of Ultrabithorax in beetle embryos outside of its endogenous expression domain affected normal development of the body wall cuticle and appendages. CONCLUSIONS: The homeotic genes have long been thought to play an important role in the diversification of arthropod appendages. Using recombinant Sindbis virus, we were able to investigate homeotic gene function in non-model arthropod species. We found that Ultrabithorax is sufficient to confer hindwing identity in butterflies and alter normal development of anterior structures in beetles. Recombinant Sindbis virus has broad potential as a tool for analyzing how the function of developmental genes has changed during the diversification of arthropods.

Animals↗
PubMed1999

The CB1 cannabinoid receptor can sequester G-proteins, making them unavailable to couple to other receptors.

We tested the hypothesis that human CB1 cannabinoid receptors (hCB1) can sequester G(i/o)-proteins from a common pool and prevent other receptors from signaling. Human CB1 cannabinoid receptors were expressed in superior cervical ganglion (SCG) neurons by microinjection of hCB1 cDNA. Expression of hCB1 cannabinoid receptors abolished the Ca(2+) current inhibition by endogenous pertussis toxin-sensitive G(i/o)-coupled receptors for norepinephrine (NE) and somatostatin (SOM) but not by endogenous pertussis toxin-insensitive G(s)-coupled receptors for vasoactive intestinal polypeptide. Signaling by NE was rescued by expression of Galpha(oB), Gbeta(1), and Ggamma(3). Expression of mGluR2 metabotropic glutamate receptors, another pertussis toxin-sensitive G-protein-coupled receptor, had no effect on the signaling by NE or SOM. Some hCB1 receptors were constitutively active because the cannabinoid receptor inverse agonist SR 141617A enhanced the Ca(2+) current. Some hCB1 receptors also appear to be precoupled to G(i/o)-proteins because the cannabinoid agonist WIN 55,212-2 decreased the Ca(2+) current at a time when no G-proteins were available to couple to alpha(2)-adrenergic and somatostatin receptors. In SCG neurons microinjected with a lower concentration of hCB1 cDNA, the effect of SR 141716A was reduced, and the response to NE and SOM was partially restored. Subsequent to the application of SR 141716A, the Ca(2+) current inhibition by NE and SOM was abolished. These results suggest that both the active and inactive states of the hCB1 receptor can sequester G(i/o)-proteins from a common pool. Cannabinoid receptors thus have the potential to prevent other G(i/o)-coupled receptors from transducing their biological signals.

Animals↗
PubMed1999

Influence of environmental changes on degradation of chiral pollutants in soils.

Numerous anthropogenic chemicals of environmental concern--including some phenoxy acid herbicides, organophosphorus insecticides, polychlorinated biphenyls, phthalates, freon substitutes and some DDT derivatives--are chiral. Their potential biological effects, such as toxicity, mutagenicity, carcinogenicity, and endocrine disrupter activity, are generally enantiomer-selective, and different enantiomers are preferentially degraded (transformed) by micro-organisms in various environments. Here we use field and laboratory experiments to demonstrate that environmental changes in soils can alter these preferences, and to suggest that the preferences shift owing to different groups of related microbial genotypes being activated by different environmental changes. In Brazilian soils, almost all pasture samples preferentially transformed the non-herbicidal enantiomer of dichlorprop ((RS)-2-(2,4-dichlorophenoxy)propionic acid), while most forest samples either transformed the herbicidal enantiomer more readily or as rapidly as the non-herbicidal enantiomer. Organic nutrient enrichments shifted enantioselectivity for methyl dichlorprop ((RS)-methyl 2-(2,4-dichlorophenoxy)propionic acid) strongly towards preferentially removing the non-herbicidal enantiomer in soils from Brazil and North America, potentially increasing phytotoxicity of its residues relative to that of the racemate. Assessments of the risks chemical pollutants pose to public health and the environment need to take into account the chiral selectivity of microbial transformation processes and their alteration by environmental changes, especially for pesticides as up to 25 per cent are chiral.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1999

Recruitment of a hedgehog regulatory circuit in butterfly eyespot evolution.

The origin of new morphological characters is a long-standing problem in evolutionary biology. Novelties arise through changes in development, but the nature of these changes is largely unknown. In butterflies, eyespots have evolved as new pattern elements that develop from special organizers called foci. Formation of these foci is associated with novel expression patterns of the Hedgehog signaling protein, its receptor Patched, the transcription factor Cubitus interruptus, and the engrailed target gene that break the conserved compartmental restrictions on this regulatory circuit in insect wings. Redeployment of preexisting regulatory circuits may be a general mechanism underlying the evolution of novelties.

Animals↗
PubMed1998

Expression pattern of a butterfly achaete-scute homolog reveals the homology of butterfly wing scales and insect sensory bristles.

BACKGROUND: Lepidopteran wing scales are the individual units of wing color patterns and were a key innovation during Lepidopteran evolution. On the basis of developmental and morphological evidence, it has been proposed that the sensory bristles of the insect peripheral nervous system and the wing scales of Lepidoptera are homologous structures. In order to determine if the developmental pathways leading to Drosophila sensory bristle and butterfly scale formation use similar genetic circuitry, we cloned, from the butterfly Precis coenia, a homolog of the Drosophila achaete-scute (AS-C) genes--which encode transcription factors that promote neural precursor formation--and examined its expression pattern during development. RESULTS: During embryonic and larval development, the expression pattern of the AS-C homolog, ASH1, forecasted neural precursor formation. ASH1 was expressed both in embryonic proneural clusters--within which an individual cell retained ASH1 expression, enlarged, segregated, and became a neural precursor--and in larval wing discs in putative sensory mother cells. ASH1 was also expressed in pupal wings, however, in evenly spaced rows of enlarged cells that had segregated from the underlying epidermis but, rather than give rise to neural structures, each cell contributed to an individual scale. CONCLUSIONS: ASH1 appears to perform multiple functions throughout butterfly development, apparently promoting the initial events of selection and formation of both neural and scale precursor cells. The similarity in the cellular and molecular processes of scale and neural precursor formation suggests that the spatial regulation of an AS-C gene was modified during Lepidopteran evolution to promote scale cell formation.

Amino Acid Sequence↗
PubMed1998

A comparison of threshold-based fitting strategies for nonlinear hearing aids.

OBJECTIVE: In recent years, wide dynamic range compression (WDRC) has been used with increasing success. To optimize the fit with this type of hearing aid circuitry, subjective measures of loudness growth often are used. Unfortunately, these type of measures cannot be performed with infants, young children, and some elderly individuals. The primary purpose of this study was to compare the fitting recommendations of two recently described threshold-based procedures for fitting nonlinear hearing aids (DSL 4.0 and FIG6) to the use gain settings of satisfied adult hearing aid users for whom the fitting was based on subjective measures of loudness growth. Because it cannot be assumed that the use settings for adults will be appropriate for young children, a secondary goal was to quantify the audibility of speech at the use settings derived from loudness growth measures. DESIGN: Forty-nine adult hearing aid users with mild to severe sensorineural hearing loss participated in this study. For all subjects, loudness growth measures were used to optimize the fit of a 2-channel WDRC hearing aid. The use gain at 50 and 80 dB SPL was compared with the gain recommended by DSL, FIG6, and the manufacturer's threshold-based fitting algorithm. RESULTS: In general, both DSL and FIG6 prescribed more gain than actually was used by these hearing aid wearers. These discrepancies increased as a function of frequency, and differences in excess of 20 dB were observed in some cases. The manufacturer's algorithm provided a closer approximation to the use gain than either DSL or FIG6. Utilizing these use gain values, an Aided Audibility Index (AAI) was calculated for soft, average, and loud speech across four degrees of hearing loss, ranging from mild to severe (12 conditions). Transfer functions for continuous discourse and nonsense syllables were applied to yield estimated intelligibility scores. For the higher context speech materials, estimated intelligibility was > or = 85% for nine of the 12 conditions. For low-context speech materials, estimated intelligibility was > or = 85% for only three of the 12 conditions. CONCLUSIONS: Results suggest that the gain recommendations provided by both DSL and FIG6 exceeded the gain actually used by the adult hearing-impaired subjects in this study. Gain recommendations from the manufacturer's algorithm provided a closer approximation to the use gain values of these subjects. These findings suggest that, for adult hearing aid users who cannot perform loudness judgments reliably, the manufacturer's algorithm would be expected to provide a closer approximation to loudness-based use gain values than either DSL or FIG6. However, AAI calculations revealed that the gain recommendations from this algorithm produce adequate audibility of speech only if one assumes linguistic competence. When AAI values are transformed to predict the intelligibility of low-context speech materials, it appears that the degree of audibility may not be appropriate for prelingually hearing-impaired children with more than a moderate hearing loss.

Aged↗
PubMed1998

SR 141716A acts as an inverse agonist to increase neuronal voltage-dependent Ca2+ currents by reversal of tonic CB1 cannabinoid receptor activity.

The CB1 cannabinoid receptor antagonist SR 141716A abolished the inhibition of Ca2+ currents by the agonist WIN 55,212-2. However, SR 141716A alone increased Ca2+ currents, with an EC50 of 32 nM, in neurons that had been microinjected with CB1 cRNA. For an antagonist to elicit an effect, some receptors must be tonically active. Evidence for tonically active CB1 receptors was seen as enhanced tonic inhibition of Ca2+ currents. Preincubation with anandamide failed to enhance the effect of SR 141716A, indicating that anandamide did not cause receptor activity. Under Ca2+-free conditions designed to block the Ca2+-dependent formation of anandamide and sn-2-arachidonylglycerol, SR 141716A again increased the Ca2+ current. The Ca2+ current was tonically inhibited in neurons expressing the mutant K192A receptor, which has no affinity for anandamide, demonstrating that this receptor is also tonically active. SR 141716A had no effect on the Ca2+ current in these neurons, but SR 141716A could still antagonize the effect of WIN 55, 212-2. Thus, the K192 site is critical for the inverse agonist activity of SR 141716A. SR 141716A appeared to become a neutral antagonist at the K192A mutant receptor. Native cannabinoid receptors were studied in male rat major pelvic ganglion neurons, where it was found that WIN 55,212-2 inhibited and SR 141716A increased Ca2+ currents. Taken together, our results demonstrate that a population of native and cloned CB1 cannabinoid receptors can exist in a tonically active state that can be reversed by SR 141716A, which acts as an inverse agonist.

Animals↗
PubMed1997

The effects of gamma-oryzanol supplementation during resistance exercise training.

To determine the effectiveness of gamma-oryzanol supplementation, weight-trained males were randomly divided into supplemented (G-O) and control placebo (Con) groups. The G-O group ingested 500 mg.day-1 of gamma-oryzanol according to manufacturer's instructions. Test batteries were administered before (T1), after 4 weeks (T2), and after 9 weeks (T3) of a periodized resistance exercise program. Both groups demonstrated significant increases in 1 repetition maximum muscular strength (bench press and squat) and vertical jump power, with no differences between the groups. No differences between groups were observed for measures of circulating concentrations of hormones (testosterone, cortisol, estradiol, growth hormone, insulin, beta-endorphin), minerals (calcium, magnesium), binding protein (albumin), or blood lipids (total cholesterol, triglycerides, HDL-cholesterol). Resting cardiovascular variables decreased similarly for both groups. These data suggest that 9 weeks of 500 mg.day-1 of gamma-oryzanol supplementation does not influence performance or related physiological parameters in moderately weight-trained males.

Adult↗
PubMed1997

Inhibition of M-type K+ and N-type Ca2+ channels by the human gonadotropin-releasing-hormone receptor heterologously expressed in adult neurons.

Gonadotropin-releasing hormone (GnRH) controls all aspects of reproductive function. GnRH is secreted by hypothalamic neurons and exerts its effects on the endocrine system through pituitary gonadotropes, while its effects on sexual receptivity are mediated by the central nervous system. The electrophysiological responses of central neurons to GnRH have shown both excitatory and inhibitory responses, but little is known about the mechanisms by which GnRH can change neuronal excitability. The present study addresses the mechanisms whereby stimulation of the human GnRH receptor changes neuronal excitability by using a combination of electrophysiological and heterologous expression techniques. Microinjection of in vitro transcribed cRNA coding for the human GnRH receptor into enzymatically dissociated adult rat superior cervical ganglion neurons resulted in GnRH receptor expression. Activation of the GnRH receptor inhibited both M-type K+ and N-type Ca2+ channels. Inhibition of M-type K+ channels was insensitive to pertussis toxin pretreatment and blocked by intracellular GDPbetaS. Inhibition of Ca2+ channels was slow in onset, voltage independent and insensitive to pertussis toxin. Wash-out of GnRH resulted in an unusual transient reversal of tonic G-protein-mediated Ca2+ channel inhibition. Block of the N-type Ca2+ channel with omega-conotoxin GVIA decreased Ca2+ current inhibition from 43 to 15%, indicating that the N-type Ca2+ channel is an effector target. Ca2+ channel inhibition was completely abolished by including a Ca2+ chelator in the patch pipette. Cell-attached macropatch experiments indicated that Ca2+ channel inhibition is mediated by a diffusible second messenger. These results demonstrate that the human GnRH receptor can inhibit M-type K+ and N-type Ca2+ channels when heterologously expressed in adult rat neurons. Modulation of M-type K+ and N-type Ca2+ channels in central neurons which contain GnRH receptors is likely to contribute to the changes in neuronal excitability elicited by GnRH.

Animals↗
PubMed1997

The prevalence of chapped lips during an army hot weather exercise.

OBJECTIVES: To identify risk factors associated with chapped lips in soldiers during prolonged exposure to a hot, dry environment. METHODS: We examined 1,053 of 2,500 soldiers (42%) participating in a desert training exercise at Fort Irwin, California, in September 1983. We measured the prevalence of chapped lips during the third week of a 4-week training period. Our independent variables (complexion, sex, lip protectant use, age, and the prevalence of recurrent herpes labialis) were obtained by observation and interview. RESULTS: We found severe chapping in 150 (10%) and moderate chapping in 247 (23.5%) of the soldiers. Stepwise ordinal logistic regression was used to identify risk factors associated with chapped lips and to determine the prevalence odds ratios (OR). Risk factors with statistically significant associations with chapped lips were the presence of recurrent herpes labialis (OR = 2.88), very fair complexion (OR = 3.23), and fair complexion (OR = 1.58). CONCLUSIONS: Moderate to severe chapping occurred in approximately one-third of the soldiers. Lip protectants appeared to be relatively ineffective in the prevention and treatment of chapped lips but were associated with a lower prevalence of recurrent herpes labialis.

Adolescent↗
PubMed1996

Catalytic subunit of mitochondrial DNA polymerase from Drosophila embryos. Cloning, bacterial overexpression, and biochemical characterization.

A full-length cDNA of the catalytic subunit of mitochondrial DNA polymerase from Drosophila embryos has been obtained, and its nucleotide sequence was determined. The cDNA clone encodes a polypeptide with a deduced amino acid sequence of 1145 residues and a predicted molecular mass of 129.9 kDa. Amino-terminal sequence analysis of the mature catalytic subunit of the heterodimeric mitochondrial enzyme from Drosophila embryos identified the amino-terminal amino acid at position +10 in the deduced amino acid sequence, indicating a mitochondrial presequence peptide of only nine amino acids. Alignment of the catalytic subunit sequence with that of Escherichia coli DNA polymerase I Klenow fragment indicated a high degree of amino acid sequence conservation in each of the three DNA polymerase and three 3' --> 5' exonuclease domains identified by biochemical studies in the latter enzyme. Bacterial overexpression, purification, and biochemical analysis demonstrated both 5' --> 3' DNA polymerase and 3' --> 5' exonuclease in the recombinant polypeptide. This represents the first demonstration of 3' --> 5' exonuclease activity in the polymerase catalytic subunit of animal mitochondrial DNA polymerase.

Amino Acid Sequence↗
PubMed1996

Rat brain cannabinoid receptor modulates N-type Ca2+ channels in a neuronal expression system.

Modulation of neuronal ion channels by the cloned rat brain CB1 cannabinoid receptor was investigated with the use of a heterologous neuronal expression system. Transient expression of the rat brain CB1 cannabinoid receptor was accomplished through microinjection of in vitro transcribed cRNA into the cytoplasm of enzymatically dissociated adult rat superior cervical ganglion neurons. The cannabimimetic aminoalkylindole WIN 55,212-2 inhibited whole-cell Ca2+ currents in neurons injected 16-25 hr previously with rat brain CB1 cannabinoid receptor cRNA. Inhibition of the Ca2+ current was voltage and concentration dependent, with a maximal inhibition of 73% and an IC50 value of 47 nM. The synthetic cannabinoid analogue CP55,940 also inhibited Ca2+ currents, with a maximal inhibition of 38% and an IC50 value of 7 nM. Ca2+ current inhibition was blocked by inclusion of guanosine-5'-O-(2-thiodiphosphate) in the intracellular patch pipette solution or by pretreatment with pertussis toxin. Pretreatment with the N-type Ca2+ channel antagonist omega-conotoxin GVIA reduced the inhibition by 100 nM WIN 55,212-2 from 44% to 6%, indicating that N-type Ca2+ channels are a target of cannabinoid action. On washout of WIN 55,212-2, the Ca2+ current amplitude "overrecovered" in 47% of the neurons tested. Anandamide, the endogenous cannabimimetic compound, had an inconsistent effect on the voltage-dependent Ca2+ currents in the majority of neurons microinjected with cannabinoid receptor cRNA. Ca2+ channels were a specific effector target of the cannabinoid receptor, as two different K+ currents, the M current and the A current, were not modulated by the cannabimimetic WIN 55,212-2.

Animals↗
PubMed1995

L- and N-type Ca2+ channels in adult rat carotid body chemoreceptor type I cells.

1. Whole-cell voltage-dependent Ca2+ currents recorded from chemoreceptor type I cells of the adult rat carotid body had maximum amplitudes of -94 pA in 10 mM Ca2+ and were half-inactivated at a holding potential of -38 mV. Somatostatin and dopamine inhibited whole-cell Ca2+ current in type I cells. 2. The dihydropyridine agonist (+)202-791 increased the Ca2+ current amplitude by 106% at a step potential of -18 mV. The dihydropyridine antagonist nimodipine decreased the Ca2+ current amplitude by 40% from a holding potential of -80 mV, and by 74% from a holding potential of -60 mV. The nimodipine-sensitive current had a maximum amplitude at a membrane potential of -12 mV. omega-Conotoxin GVIA (omega-CgTX GVIA) blocked the whole-cell Ca2+ current by 40%. The omega-CgTX GVIA-sensitive current had a maximum amplitude at a membrane potential of +2 mV. 3. In summary, type I cells of the adult rat carotid body have dihydropyridine-sensitive L-type and omega-conotoxin GVIA-sensitive N-type voltage-dependent Ca2+ channels. These channels may play a role in the voltage-gated entry of Ca2+ necessary for stimulus-secretion coupling in response to changes in arterial PO2, PCO2 and pH. Inhibition of the Ca2+ currents by somatostatin and dopamine may alter the chemotransduction signal in type I cells.

Animals↗
PubMed1995

Heterologous expression of metabotropic glutamate receptors in adult rat sympathetic neurons: subtype-specific coupling to ion channels.

A novel heterologous expression system was used to examine the coupling of metabotropic glutamate receptors (mGluRs) to neuronal voltage-gated ion channels. Cytoplasmic injection of mGluR2 cRNA into adult rat sympathetic neurons resulted in the expression of receptors that negatively coupled to N-type Ca2+ channels through a pertussis toxin-sensitive pathway. Injection of mGluR1 alpha cRNA resulted in the expression of receptors that inhibited M-type K+ channels via a pertussis toxin-insensitive pathway. Coupling was restricted to specific transduction elements and effectors, since mGluR2 did not inhibit M channels and mGluR1 alpha had minimal effects on Ca2+ channels. These findings demonstrate that heterologously expressed, and thus unambiguously identified, mGluR subtypes modulate specific neuronal ion channels through discrete signal transduction pathways.

Animals↗