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C Louis

Publications and source records attributed to C Louis.

At least 73 records · Page 4Linked to original sources
PubMed1994

Polymorphisms detected by random PCR distinguish between different chromosomal forms of Anopheles gambiae.

We have applied PCR amplification using random primers to distinguish between incipient species of the malaria vector Anopheles gambiae. Individuals belonging to three chromosomally characterized West African forms of this mosquito, which are important epidemiologically as they differ in vectorial capacity, were sampled both from laboratory stocks and from wild populations collected in three localities. The techniques used allowed for the unambiguous classification of the mosquitoes, providing a tool for rapid and efficient diagnosis, which previously relied on cytological examination of polytene chromosomes.

Africa, Western↗
PubMed1994

Interaction between the aphid transmission factor and virus particles is a part of the molecular mechanism of cauliflower mosaic virus aphid transmission.

Cauliflower mosaic virus (CaMV) aphid transmission factor (ATF or P18) is presumed to interact with both virus particles and vector mouthparts, thereby mediating virus aphid transmission. We developed a protein-protein binding assay and our results clearly show that virus particles bind strongly and specifically to P18 whether P18 was obtained from plants, a baculovirus expression system, or the pGEX-3X Escherichia coli expression system. We overproduced, using the pGEX-3X expression system, various fragments of P18 and thereby demonstrated that the C-terminal 31 amino acid residues are responsible for the interaction. Using PCR-based mutagenesis, 2 amino acid residues essential for interaction were identified. Point substitutions (amino acids 157 from Ile to Asn or 159 from Gly to Ser) were sufficient to abolish the interaction, whereas another mutation (amino acid 158 from Ile to Ser) had no effect on P18 virus binding. We evaluated whether there was a correlation between the ability of P18 to interact with CaMV particles and its biological activity. Aphid transmission assays were carried out and we demonstrated that the loss of the virus binding capacity had a dramatic effect on the ability of P18 to mediate aphid transmission. Thus, our results suggest that binding between P18 and virus particles is likely to be one of the molecular mechanisms involved in CaMV aphid transmission.

Animals↗
PubMed1994

Analysis of the Anopheles gambiae genome using RAPD markers.

RAPD analysis technique is used as a rapid and reliable tool for genome analysis in the malaria vector Anopheles gambiae. Using more than eighty different commercially available primers we identified more than sixty different DNA segments that were differentially amplified in different strains of An. gambiae s.s. and An. arabiensis. An estimate of the cytogenetic position of these markers is provided by their hybridization to divisional dot-blot filters. Potentially useful RAPD markers can be cytogenetically mapped with more precision by in situ hybridization and, as they segregate as dominant markers in a Mendelian fashion, they can also be genetically mapped relative to other genes or rearrangements. Finally, we identified markers for their potential use in the identification of different mosquito strains.

Animals↗
PubMed1994

DDI pacing: indications, expectations, and follow-up.

The DDI mode of pacing that permits noncompetitive atrioventricular sequential bradycardia support was chosen in 65 of 480 (14%) patients selected for dual chamber pacing between February 1985 and March 1990. All patients were implanted with Pacesetter 283 or 285 pulse generators and programmed to DDI. The indications for pacing were sick sinus syndrome (n = 52), combined sinus node dysfunction and AV block (n = 13). Forty-two of these patients had a history of paroxysmal atrial arrhythmias. All patients received passive fixation atrial and ventricular leads. Follow-up thereafter was performed predischarge, and at 6 weeks, 3 and 6 months after discharge. The duration of follow-up ranged from 1-61 months (mean 31 months). Fifty-four of 65 (83%) patients chosen for DDI remain programmed in the DDI mode. Three patients were reprogrammed to VVI and eight to DDD. During the course of follow-up, six patients presented with effective VVI pacing with consistent ventriculoatrial conduction that was appropriately sensed by the atrial circuit with atrial output inhibition. A further four patients presented with "functional undersensing" due to ventricular blanking period (VBP) characteristics in these pulse generators and in this mode. Functional undersensing was eliminated in all but one patient by reprogramming the VBP to 13 msec with no subsequent episodes of provoked crosstalk inhibition. Effective VVI pacing was observed in patients with AV block during times of sinus acceleration.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Attenuation of white gene expression in transgenic Drosophila melanogaster: possible role of a catalytic antisense RNA.

We have transformed Drosophila melanogaster with a DNA construct encoding a catalytic antisense RNA directed against the primary white gene RNA transcript. Total RNA isolated from transformed flies was shown to catalyze the specific cleavage of in vitro transcribed substrate RNA, indicating the expression of a functional ribozyme. Moreover, transgenic lines carrying homozygous copies of this construct depict a further clear-cut reduction in eye pigmentation when present in a genetic background that has a priori reduced levels of white gene expression.

Alleles↗
PubMed1993

Gene II product of an aphid-nontransmissible isolate of cauliflower mosaic virus expressed in a baculovirus system possesses aphid transmission factor activity.

A new baculovirus expression system was used to express the gene II which encodes the 18-kDa aphid transmission factor (ATF) protein of two isolates of cauliflower mosaic virus (CaMV), the aphid-transmissible (AT+) Cabb B-JI and the aphid-nontransmissible (AT-) CM1841 isolates. ATF activity was shown to be associated with the baculovirus expression product of CaMV gene II from both the AT+ and the AT- isolates. No differences could be detected in the stability of the P18s from AT+ and AT- isolates expressed in the baculovirus system. These results indicate that the AT- phenotype of CM1841 isolate might not be due to a defective P18 but to an insufficient concentration of it in infected plant tissue.

Animals↗
PubMed1993

Paracrystalline structure of cauliflower mosaic virus aphid transmission factor produced both in plants and in a heterologous system and relationship with a solubilized active form.

Cauliflower mosaic virus (CaMV) aphid transmission factor (ATF), produced in a baculovirus expression system, forms paracrystalline structures, as demonstrated by electron microscopic observations. Similar paracrystals were also found in CaMV-infected plants, using immunogold techniques, thus providing the first evidence of such a structure for the CaMV ATF (P18). We demonstrated that the paracrystals can be solubilized to provide an active form of the CaMV ATF which can also be reverted into the paracrystalline aggregated form. This suggests that the paracrystalline structures might act as a source of active CaMV ATF or be the form in which it is stored within the infected cells. A point mutation within the CaMV gene II (which encodes the ATF) leads to the loss of both the paracrystalline structures and the ATF activity. Hence, the paracrystalline structure seems to be a feature of the native (unmodified ) CaMV ATF.

Animals↗
PubMed1993

Opa-like repeats in the genome of the Medfly Ceratitis capitata.

The sequence determination of several genomic clones isolated from the Mediterranean fruitfly Ceratitis capitata identified the existence of opa-like repeats, often more than one being clustered in small chromosomal segments. These repeats have previously been shown to consist of stretches of tandemly reiterated glutamine-encoding residues, and they are found in multiple genes of several organisms. Most of the repeats described here are flanked or interrupted by stop codons in all reading frames and, thus, could not possibly be part of protein-coding sequences. Furthermore, these repeats, of which there are several hundred in the genome of the Medfly, can be used effectively for the determination of sequence polymorphisms, providing a convenient approach to obtain additional landmarks for the construction of genomic maps of this economically important insect.

Amino Acid Sequence↗
PubMed1993

[Unusual intrathoracic tumor in children: lipoma].

BACKGROUND: Intrathoracic lipomas are rare, often asymptomatic and, in this case, discovered by chance on X-ray. CASE REPORT: A 3 year-old girl was admitted because chest X-rays prescribed for a persistent cough showed a mass in the right axillary area. The CT scan showed a mass with density of -80 Hounsfield units, characteristic of adipose tissue. There was a slight rib change in contact with the mass, but radionuclide bone scan showed no area of increased uptake. A chest X-ray performed 3 years earlier had shown such a mass, but it was not recognized at that time. Surgery demonstrated that the mass was extrapleural in location and adhering to the rib which was partly excised. Histologic examination showed the presence of mature adipocytes, but no malignant cells. CONCLUSION: The fatty component of an intrathoracic tumor is easily recognized with CT scan. Erosion of bone in contact with it has been reported.

Age Factors↗
PubMed1992

Two non-gypsy rudimentary mutations and their suppression by mutations of suppressor of Hairy-wing in Drosophila.

Two spontaneous mutations of rudimentary, the gene encoding the first steps of de novo pyrimidine biosynthesis in Drosophila, are suppressed by mutant alleles of the suppressor of Hairy-wing locus. This interaction differs from typical su(Hw) suppression in that neither rudimentary allele is associated with an insertion of the gypsy retrotransposon. One allele, rsP1, appears to be a point mutation. Adult rsP1 homozygous females accumulate substantially less 7.3 kb rudimentary transcript than do wild-type females. The other allele, rsP2, is an insertion of an mdg3 retrotransposon in the sixth exon of rudimentary and in the opposite transcriptional orientation. This insertion divides the rudimentary locus into two separate, yet functional, transcription units by truncating transcription from the rudimentary promoter and promoting transcription of downstream rudimentary sequences. Phenotypic suppression of both rsP1 and rsP2 by mutant alleles of the suppressor of Hairy-wing locus correlates with enhanced levels of the rsP1 and rsP2 transcripts.

Alleles↗
PubMed1992

Surgical management of duplex ureteroceles.

We reviewed the cases of 95 children with duplex ureteroceles treated in this department over an 18-year period. There were 101 ureteroceles (6 bilateral). Diagnosis and treatment were analyzed. Special attention was paid to newborns screened in utero. We always strove to preserve functional renal tissue whenever possible. In keeping with this goal, three surgical techniques were used: (1) upper pole heminephrectomy; (2) ureterocele excision, bladder neck reconstruction, and ureter reimplantation with or without cutaneous ureterostomy of the upper pole ureter; and (3) endoscopic ureterocele incision. Follow-up studies using x-ray and radionuclide imaging demonstrated satisfactory renal function in 86.6% of patients. These findings support a conservative approach to ureteroceles using endoscopic ureterocele incision as the primary treatment. Lower urinary tract reconstruction may be associated in cases involving urinary tract infection, obstruction or incontinence. Upper pole heminephrectomy should be performed only after functional evaluation following ureterocele incision or cutaneous ureterostomy.

Adolescent↗
PubMed1992

The distribution of the fiber cell intrinsic membrane proteins MP20 and connexin46 in the bovine lens.

MP20 is an intrinsic membrane protein previously identified in mammalian lens fiber cells. To identify a possible role for this protein in the lens, the distribution of MP20 and connexin46 has now been examined. Western immunoblotting with an anti-peptide antibody generated to the C-terminal 8 amino acids of MP20 confirmed the presence of this protein in the lens of several different mammalian species. A monoclonal antibody 5H1 was prepared that, in Western blots of bovine lesn membranes, recognized the same component as an antibody to rat connexin46 (Cx46). The apparent molecular mass of this component decreased from 59 kDa to 55 kDa following treatment of lens membranes with alkaline phosphatase. A monoclonal antibody to connexin-related MP70 recognized a 70 kDa component in bovine lens membranes confirming the presence of these two different connexin proteins in bovine lens membranes. To localize MP20 and Cx46 in the bovine lens membrane, lens fiber cell bundles were immunofluorescently labeled with both the MP20 antibody, and the monoclonal antibody to Cx46. Cx46 was identified in large plaques on the broad faces of the lens fiber cells throughout the outer 1 mm of the lens cortex. MP20 colocalized with Cx46 only in a restricted area 0.5 mm to 1.0 mm into the lens. In other regions of the lens, MP20 appeared more diffusely distributed over the fiber cell surface, although apparently concentrated in the ball-and-socket regions at the corners of the narrow side of the inner cortical lens fiber cells. These inner cortical regions were devoid of Cx46. A difference in distribution of these two proteins was confirmed in studies of immunofluorescently labeled lens cryosections. Furthermore, immunogold electron microscopy of purified lens membranes identified MP20 in both junctional regions (with Cx46) and in single membranes. These results provide evidence for a role for MP20 in mammalian lens fiber cell junctional formation or organization.

Animals↗
PubMed1991

Masculinization of female isopods (Crustacea) correlated with non-Mendelian inheritance of cytoplasmic viruses.

When in genetic females external male characters differentiate, the phenomenon is called "male pseudohermaphroditism." This male differentiation occurs in terrestrial isopods (Crustacea, suborder Oniscoidea) and sometimes involves only some epithelial areas (gynandromorphous mosaics). It is not induced by male hormones or by abnormal ovary function. This intersexuality is transmitted maternally (by the intersex females) or paternally (by the brothers of intersex females) to between 30% and 60% of their offspring. Although it occurs at 20 degrees C, the male differentiation disappears when breeding takes place at 27 degrees C. Male characters differentiate in normal females--even in other Oniscoidea species (Porcellio dilatatus, Porcellio laevis, Armadillidium vulgare)--after injection of a 0.22-micron filtered tissue extract. Since an inhibitor of bacterial protein synthesis (gentamycin) does not inhibit this masculinizing effect, we infer that neither organelles nor bacteria are involved. Intersexuality is always correlated with the presence of cytoplasmic viral particles in both intersex-female and transmitter-male tissues. Striking similarities to the Drosophila S virus are noted. A reovirus-like Oniscoidea masculinizing virus, which probably acts only on the epithelial areas sensitive to the male hormones, is most likely the causative agent of this intersexuality. Here we report the conversion of secondary sexual characters putatively caused by a virus.

Journal Article↗
PubMed1991

Integrated maps of the Drosophila genome: progress and prospects.

A physical map of the Drosophila melanogaster genome is being assembled, consisting of ordered overlapping cosmid clones. The map is constructed in steps, separately for each chromosomal division. Gaps in this map are to be bridged with yeast artificial chromosome clones. Hybridization to previously cloned genes and extensive use of in situ hybridization to polytene chromosomes ensure that the cosmid map is firmly anchored to the wealth of available genetic and cytogenetic information. The intention is to make the physical map widely available as part of an overall, integrated genetic resource for the Drosophila research community.

Animals↗