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L Garnier

Publications and source records attributed to L Garnier.

At least 19 recordsLinked to original sources
PubMed2005

Ant navigation en route to the goal: signature routes facilitate way-finding of Gigantiops destructor.

We investigated in laboratory conditions how foragers of the tropical ant Gigantiops destructor develop individually distinctive landmark routes. Way-finding along a familiar route involved the recognition of at least two locations, nest and feeding site, and the representation of spatial relations between these places. Familiar visual landmarks were important both at the beginning and at the end of the foraging journey. A motor routine guided the ants at the start of their foraging path towards the first landmarks, which they learnt to pass consistently on the same side, before taking the next direction. At the last stage of the route, landmark recognition allowed them to pinpoint their preferred feeding site without using distant cues or odometric information. By contrast, ants en route to the goal were not systematically guided by a stereotyped sequence of snapshots recalled at each corresponding stage of the route. Each ant slalomed in an idiosyncratic distinctive way around different midway landmarks from a foraging excursion to the next, which induced a variability of the path shapes in their intermediate parts. By reducing the number of landmark recognition-triggered responses, this economical visuomotor strategy may be helpful in the Amazonian forest where many prominent landmarks are alike.

Animals↗
PubMed2003

Roles of tert-butyl formate, tert-butyl alcohol and acetone in the regulation of methyl tert-butyl ether degradation by Mycobacterium austroafricanum IFP 2012.

Mycobacterium austroafricanum IFP 2012 is a Gram-positive strain able to grow on methyl tert-butyl ether (MTBE) as a sole carbon and energy source. The effect of two downstream metabolites of MTBE, tert-butyl formate (TBF) and tert-butyl alcohol (TBA) on MTBE degradation was investigated using resting cells. The addition of low concentrations of TBF decreased the MTBE degradation rate by about 30%. In contrast, the addition of TBA did not have a significant effect on MTBE degradation rate, even at high concentrations; and it was also shown that TBA degradation occurred only once MTBE was exhausted. At neutral pH, TBF hydrolysis involved mainly an esterase-type activity regulated by the presence of TBA. The TBF degradation rate was about four times lower than the MTBE degradation rate. Furthermore, acetone was identified as an intermediate during TBA degradation. An acetone mono-oxygenase activity, inhibited by methimazole but not by acetylene, was suggested. It was different from the MTBE/TBA mono-oxygenase and, thus, acetone did not appear to compete with MTBE and TBA for the same enzyme. These new results show that the metabolic regulation of the early steps of MTBE degradation by M. austroafricanum IFP 2012 is complex, involving inhibition and competition phenomena.

Biodegradation, Environmental↗
PubMed2000

Differential budding efficiencies of human T-cell leukemia virus type I (HTLV-I) Gag and Gag-Pro polyproteins from insect and mammalian cells.

In this study, we examined the ability of human T-cell leukemia virus type I (HTLV-I) Gag and Gag-Pro to assemble immature virus-like particles (VLPs) and bud from insect and mammalian cells. Transmission electron microscopy of insect cells infected with a recombinant baculovirus carrying the entire gag gene revealed that Pr53(Gag) is targeted to the plasma membrane, where it extensively accumulates and forms electron-dense evaginations. However, no particles could be detected either inside the cells or in the culture supernatants. With the Gag-Pro-expressing construct, we observed HTLV-I-specific cytoplasmic proteolysis of the Gag precursor, but again no particle released in the culture supernatants. Transmission electron microscopic analysis of insect cells expressing Gag-Pro polyprotein revealed large vacuoles in the cytoplasm and no budding particles at the plasma membrane. In contrast, human immunodeficiency virus type 1 Gag polyprotein expressed in insect cells is able to release VLPs. These data showed that unlike other retroviruses, Pr53(Gag) is unable to be released as immature VLPs from insect cells. To determine whether the block in particle budding and release is due to an intrinsic property of Pr53(Gag) or the absence of essential cellular factors in insect cells, we expressed Gag and Gag-Pro polyproteins in human 293 cells. The results indicate that Pr53(Gag) and p24 capsid are released within particles into the culture supernatants of human 293 cells. We found that the myristylation of the N-terminal glycine residue is essential for Gag release. Altogether, these results strongly suggest that the proper assembly of HTLV-I particles is dependent on mammalian host cell factors.

Animals↗
PubMed2000

Gene flow in a facultative apomictic poacea, the savanna grass Hyparrhenia diplandra.

The genetics of the poacea Hyparrhenia diplandra was studied in four natural populations from an ecological station in West Africa, where it makes up 80% of grasses from wet savanna and constitutes a dense continuum of randomly distributed individuals. DNA content and cytogenetical observations suggest it is an allotetraploid. Using two highly variable microsatellites (heterozygosity H = 0.615-0.616), we show that this species is an apomict with rare sexual reproduction events that account for approximately 0.5% of seeds pollinated in the wild. Hexaploid individuals were also produced, corroborating the observation of aberrant genotypes in the wild. The spatial extent of asexual clones in the field was low in comparison with the predominance of apomixis, thus indicating a low dispersal of seeds from their parent. Heterozygosity and departure from Hardy-Weinberg predictions were similar in the four populations, revealing a high apparent selfing rate s = 0.599 among sexually produced seeds. This is an overestimate since we could not distinguish true selfing from reciprocal outcrosses between neighboring individuals from the same apomictic clone. Gene flow by pollen could be substantial, possibly explaining the absence of isolation by distance in the studied area.

Africa, Western↗
PubMed1999

Identification of retroviral late domains as determinants of particle size.

Retroviral Gag proteins, in the absence of any other viral products, induce budding and release of spherical, virus-like particles from the plasma membrane. Gag-produced particles, like those of authentic retrovirions, are not uniform in diameter but nevertheless fall within a fairly narrow distribution of sizes. For the human immunodeficiency virus type 1 (HIV-1) Gag protein, we recently reported that elements important for controlling particle size are contained within the C-terminal region of Gag, especially within the p6 sequence (L. Garnier, L. Ratner, B. Rovinski, S.-X. Cao, and J. W. Wills, J. Virol. 72:4667-4677, 1998). Deletions and substitutions throughout this sequence result in the release of very large particles. Because the size determinant could not be mapped to any one of the previously defined functions within p6, it seemed likely that its activity requires the overall proper folding of this region of Gag. This left open the possibility of the size determinant residing in a subdomain of p6, and in this study, we examined whether the late domain (the region of Gag that is critical for the virus-cell separation step) is involved in controlling particle size. We found that particles of normal size are produced when p6 is replaced with the totally unrelated late domain sequences from Rous sarcoma virus (contained in its p2b sequence) or equine infectious anemia virus (contained in p9). In addition, we found that the large particles released in the absence of p6 require the entire CA and adjacent spacer peptide sequences, whereas these internal sequences of HIV-1 Gag are not needed for budding (or proper size) when a late domain is present. Thus, it appears the requirements for budding are very different in the presence and absence of p6.

Animals↗
PubMed1998

Particle size determinants in the human immunodeficiency virus type 1 Gag protein.

The retroviral Gag protein plays the central role in the assembly process and can form membrane-enclosed, virus-like particles in the absence of any other viral products. These particles are similar to authentic virions in density and size. Three small domains of the human immunodeficiency virus type 1 (HIV-1) Gag protein have been previously identified as being important for budding. Regions that lie outside these domains can be deleted without any effect on particle release or density. However, the regions of Gag that control the size of HIV-1 particles are less well understood. In the case of Rous sarcoma virus (RSV), the size determinant maps to the CA (capsid) and adjacent spacer sequences within Gag, but systematic mapping of the HIV Gag protein has not been reported. To locate the size determinants of HIV-1, we analyzed a large collection of Gag mutants. To our surprise, all mutants with defects in the MA (matrix), CA, and the N-terminal part of NC (nucleocapsid) sequences produced dense particles of normal size, suggesting that oncoviruses (RSV) and lentiviruses (HIV-1) have different size-controlling elements. The most important region found to be critical for determining HIV-1 particle size is the p6 sequence. Particles lacking all or small parts of p6 were uniform in size distribution but very large as measured by rate zonal gradients. Further evidence for this novel function of p6 was obtained by placing this sequence at the C terminus of RSV CA mutants that produce heterogeneously sized particles. We found that the RSV-p6 chimeras produced normally sized particles. Thus, we present evidence that the entire p6 sequence plays a role in determining the size of a retroviral particle.

HIV Core Protein p24↗
PubMed1996

Involvement of the vagus nerve, substance P and cholecystokinin in the regulation of intestinal blood flow.

Intestinal blood flow was recorded in anesthetized rats and cats using laser-Doppler flowmetry (LDF). This new technique provides continuous and accurate measurements of the intestinal blood flow, without affecting the blood circulation. Electrical stimulation (1 ms, 5-30 V, 5-50 Hz) applied either afferent or efferent vagal fibres elicited changes in the intestinal blood flow consisting mainly of increases. Similar results were obtained upon applying chemical stimulation to intestinal sensory endings using cholecystokinin (CCK) or substrance P (SP; 10-20 micrograms/kg intravenously given). Bilateral vagotomy and atropine treatment markedly reduced or suppressed these vascular effects. In addition experiments in which the activation of gastrointestinal afferents were activated by applying electrical stimulation to the abdominal vagal nerves yielded similar results. Finally, these effects were reduced after selectively severing vagal afferents. It is concluded that intestinal blood changes may be triggered by activation of the sensory endings from the digestive organs through the vagal nerves.

Afferent Pathways↗
PubMed1995

The intracellular domain of the rabbit prolactin receptor is able to promote the secretion of a passenger protein via an unusual secretory pathway in lepidopteran cells.

We have previously shown that the intracellular domain of the rabbit prolactin receptor (rbPRL-R), lacking typical signal sequences, was very efficiently secreted into the culture medium when expressed in the baculovirus-insect cell system. We have sought to take advantage of this characteristic for secreting cytoplasmic or nuclear proteins. We have constructed a series of recombinant viruses expressing a foreign gene product fused to the intracellular domain of rbPRL-R. Two passenger genes were used, one encoding a cytoplasmic protein (cyclin B) and the other a nuclear protein (cyclin A). The intracellular domain of rbPRL-R was able to promote the export of these two chimeric proteins with a very high efficiency. This new system should prove useful for secretion of proteins which do not require the post-translational modifications of the classical secretory pathway to be fully active.

Animals↗
PubMed1995

Incorporation of pseudorabies virus gD into human immunodeficiency virus type 1 Gag particles produced in baculovirus-infected cells.

The human immunodeficiency virus type 1 (HIV-1) Pr55gag precursors were previously shown to assemble and bud efficiently as noninfectious virus-like particles (VLPs) when expressed in baculovirus-infected insect cells. In this study, we examined the abilities of foreign antigens to be incorporated on the outer surface of HIV-1 Gag particles. We have used a dual recombinant baculovirus, expressing the HIV-1 Gag gene and gD gene under the control of the P10 and polyhedrin promoters, respectively, to obtain hybrid VLPs. Transmission electron microscopy of insect cells infected with the dual recombinant revealed very large aggregates of particles budding from the cell membrane. The release of VLPs into the culture medium was clearly different for a recombinant baculovirus producing solely HIV-1 Gag, for which particles were uniformly distributed all around the cell surface. Biochemical analysis of hybrid particles indicated that glycoprotein gD was packaged into HIV-1 Gag VLPs. Moreover, the carboxy-terminal p6 region of Gag polyprotein and the glycoprotein gD intracytoplasmic domain were not required for gD incorporation. The experiments described here clearly demonstrate that glycoprotein gD can be packaged with HIV-1 Gag particles and released from insect cells.

Animals↗
PubMed1994

Evidence for N-glycosylation and ubiquitination of the prolactin receptor expressed in a baculovirus-insect cell system.

The molecular mass of the rabbit prolactin receptor (rbPRLR) deduced from cDNA cloning is 66 kDa. However, the molecular mass of the full-length receptor expressed in the insect Sf9 cells was found to be 94 kDa. In order to explain this discrepancy, we analyzed the possible post-translational modifications of the PRLR. Sf9 cells were infected with recombinant baculoviruses in the presence of tunicamycin, an inhibitor of N-glycosylation. Results showed that an additional approximately 9 kDa of the extracellular domain could be attributed to the N-glycosylation and another additional approximately 20 kDa covalent modification occurred in the cytoplasmic part of the receptor. Western blot analysis, using anti-ubiquitin antibodies, revealed that the rbPRLR was ubiquitinated in its cytoplasmic domain.

Animals↗
PubMed1994

Quantitative studies of fly visual sustained neurons.

We present a quantitative study of a neural network model [1] proposed for the sustained neurons in the fly visual system. Electrophysiological recordings of sustained neurons [2] are digitized and transferred to a computer. A numerical ordinary differential equation solver is used to simulate the model. In order to obtain an initial set of parameters, we introduce approximations to the model and obtain fits to parts of the response characteristics. These initial parameter values are then refined by optimization routines. The model is compared to data in 4 different experimental paradigms and in general is in good agreement with data. We conclude that the simplified versions of temporal and spatial adaptation mechanisms of the model capture the essential features of the dynamics of sustained neurons and that the refinement of the model requires further experimental studies to elucidate the number of stages involved in temporal adaptation as well as the precise shape of the relationship between the membrane potentials and the spike frequency for the sustained neurons.

Action Potentials↗
PubMed1990

[Pyeloduodenal fistula. Apropos of a new case].

A pyelo duodenal fistula is rarely observed although anatomical relations between the high urinary tract and digestive tractus are closed. The authors report here a new observation of pyelo-duodenal fistula and make correlations with the 73 observations published in mondial literature. Spontaneous fistulas from urinary etiology are the most frequent. This urinary pathology is revealed by general and digestive signs. Duodenal fistula could usually be stiched up. Renal destruction require nephrectomy.

Aged↗
PubMed1986

Osmosensitive vagal receptors in the small intestine of the cat.

In anesthetized cats, the unitary activity of 66 sensory vagal neurones was recorded with extracellular glass microelectrodes implanted in the nodose ganglia. These neurones had non-medullated afferent fibres with conduction velocities between 0.8 and 1.2 m/s, as do most of the intestinal vagal fibres, and were silent or fired at low frequencies before any simulation. They were activated by perfusion of the small intestine (duodenum and first part of jejunum) with tap water and various solutions (glucose, NaCl and mannitol, in particular) having osmotic pressures ranged between 4 and 1100 mOsm. In general, hypotonic solutions and tap water induced the more marked responses, but differences were observed according to the solution used. Most of these neurones were also excited by other forms of stimulation including stroking of the mucosa and perfusion with warm (39-55 degrees C) and acid (HCl at pH 1) solutions. Therefore they must be considered to be polymodal receptors sensitive to osmotic pressure. The short latency of responses elicited by osmotic stimulations, the marked sensitivity to mucosal stroking and the disappearance of nervous activity after local anesthesia indicate that these receptors are located close to the epithelium. The role of these osmosensitive endings is discussed. Analysis of their general characteristics suggests that they may be involved in the inhibitory entero-gastric reflex modulating gastric emptying.

Action Potentials↗
PubMed1986

Further data on the inhibitory enterogastric reflex triggered by intestinal osmotic changes in cats.

The relationship between osmotic pressure in the intestinal lumen and gastric motor activity was studied in anesthetized cats. For this purpose the EMG was recorded in the antrum while the small intestine (duodenum and the first part of jejunum) was perfused with various solutions: tap water (5 mOsm), NaCl, mannitol and glucose having an osmotic pressure of 70, 138, 275, 550 or 1100 mOsm. Hypotonic and hypertonic solutions both induced a decrease in the gastric activity, i.e. an increase in period of electrical control activity. This effect was found to depend both on the osmolarity value (the osmotic pressures furthest removed from the isotonic value produced the greatest effect) and on the substance used (glucose, mannitol and NaCl, in decreasing order of efficiency). The isotonic solution of glucose and, to a lesser extent, of mannitol was also active, unlike the isotonic solution of NaCl. All these gastric changes were prevented by cervical bivagotomy. It was concluded that the vagal osmosensitive receptors located in the small intestine trigger this inhibitory enterogastric reflex which probably constitutes an important part in the regulation of gastric emptying.

Action Potentials↗
PubMed1983

Bulbo-spinal respiratory effects originating from the splanchnic afferents.

Phrenic nerve responses to non-hypertensive stimulation of the visceral afferents originating from the pancreatico-duodenal area and running along the greater splanchnic nerve were studied on cats anaesthetized with sodium thiopentone, paralysed with gallamine and vagotomized. In these intact animals, a biphasic response, short activation followed by a long inhibition, was recorded in the phrenic nerve. In animals then spinalized between C1 and C2 this splanchnico-phrenic reflex persisted. The latency of the first phase was unchanged, but its amplitude increased. In intact animals, the unitary activity of 16 inspiratory neurons and 10 expiratory neurons was recorded in the part of the medulla oblongata corresponding to the ventral respiratory group. Simultaneously the overall activity of the contralateral phrenic nerve was recorded. The stimulation of splanchnic afferents caused a long inhibition of the bulbar inspiratory neurons and an activation of the expiratory neurons. The latency of the bulbar inhibition was consistently less than the latency of the phrenic inhibition. The fact that this reflex effect persisted in spinal animals with an activation phase of the same latency proves that the bulbar centres and the phrenic motoneurons are independently connected to the splanchnic afferents. The possible functional significance of the reflex is discussed.

Animals↗