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Biomedical subjects

F H Collins

Publications and source records attributed to F H Collins.

123 records · Page 7Linked to original sources
PubMed1986

Genetic selection of a Plasmodium-refractory strain of the malaria vector Anopheles gambiae.

The anopheline mosquito is the target in most malaria control programs, primarily through the use of residual insecticides. A mosquito was studied that is refractory to most species of malaria through a genetically controlled mechanism. A strain of Anopheles gambiae, which was selected for complete refractoriness to the simian malaria parasite Plasmodium cynomolgi, also has varying degrees of refractoriness to most other malaria species examined, including the human parasites P. falciparum, P. ovale, and P. vivax for which this mosquito is the principal African vector. Furthermore, the refractoriness extends to other subhuman primate malarias, to rodent malaria, and to avian malaria. Refractoriness is manifested by encapsulation of the malaria ookinete after it completes its passage through the mosquito midgut, approximately 16 to 24 hours after ingestion of an infective blood meal. Fully encapsulated ookinetes show no abnormalities in parasite organelles, suggesting that refractoriness is due to an enhanced ability of the host to recognize the living parasite rather than to a passive encapsulation of a dead or dying parasite. Production of fully refractory and fully susceptible mosquito strains was achieved through a short series of selective breeding steps. This result indicates a relatively simple genetic basis for refractoriness. In addition to the value these strains may serve in general studies of insect immune mechanisms, this finding encourages consideration of genetic manipulation of natural vector populations as a malaria control strategy.

Animals↗
PubMed1984

Identification of malaria-infected mosquitoes by a two-site enzyme-linked immunosorbent assay.

A micro enzyme-linked immunosorbent assay (ELISA) for identifying malaria sporozoites in mosquitoes is described. Using an extract of dried infected mosquitoes as antigen, a two-site ELISA was sensitive enough to detect one infected mosquito in a pool of 20. The species specificity, sensitivity and ease of performance of this assay, as well as the stability of the reagent, should make it a useful epidemiological tool.

Animals↗
PubMed1984

First field trial of an immunoradiometric assay for the detection of malaria sporozoites in mosquitoes.

An immunoradiometric assay (IRMA) using a monoclonal antibody to the major surface protein of Plasmodium falciparum sporozoites was used to assess the P. falciparum sporozoite rate in a West African population of Anopheles gambiae (s.1.). Unlike current dissection techniques, the IRMA could detect sporozoite antigen in dried as well as fresh mosquitoes. In a controlled comparison, the sensitivity of the IRMA was comparable that of the dissection technique. Additionally, the IRMA was species specific and quantitative. Sensitivity of the assay was sufficient to detect sporozoite infections resulting from the development of a single oocyst.

Animals↗
PubMed1979

Assessing personality factors in essential hypertension with a brief self-report instrument.

A 16-item self-report instrument was designed and cross-validated, comparing essential hypertensives with normotensives. After item selection using two sets of standardization groups, scores obtained from three additional sets of hypertensive and normotensive groups were significantly different. The scores were not significantly related to variables such as age, sex, socioeconomic status, hypochondriasis, social desirability or target organ involvement. The instrument's factorial structure for hypertensives consisted of factors labeled anger arousal, resentment, anxiety, and attention seeking. Hypertensives reported higher levels of hostility and anxiety than normotensives. High and low scoring subgroups on the instrument were examined on the 16 PF, with hypertensive high scorers demonstrating a different profile than low scoring hypertensives. The existence of two psychological types of essential hypertensives was suggested.

Adult↗
PubMedDate not supplied

The reservoir of Plasmodium falciparum malaria in a holoendemic area of western Kenya.

The reservoir of infectious Plasmodium falciparum gametocytes in a population living in an area of holoendemic malaria in western Kenya was estimated by directly feeding mosquitoes on volunteers. Resulting mosquito infections were assessed both by midgut examination for oocysts and by enzyme-linked immunosorbent assay for P. falciparum circumsporozoite antigen. Calculations based on the age structure of the population and the resulting rates of mosquito infections indicated that children under 10 years of age were responsible for 72% of mosquito infections, individuals between 10 and 21 years of age contributed 12%, and those over 21 years of age accounted for 16%. No infection resulted in mosquitoes fed on infants less than 1 year of age.

Age Factors↗
PubMedDate not supplied

Characterization of the Hox cluster from the mosquito Anopheles gambiae (Diptera: Culicidae).

The Hox genes have been found to encode transcription factors, which specify the morphological identity of structures along the anteroposterior axis of animals ranging from worms to mice. The canonical set of nine genes is organized in a cluster in the genome of several protostomes and deuterostomes. However, within insects, whereas the Hox genes are organized in a single cluster in the beetle Tribolium castaneum, they are split into two separate groups in the flies Drosophila melanogaster and Drosophila virilis. The significance of a split Hox cluster is unknown and has been observed in only one organism outside the Drosophila lineage: the nematode Caenorhabditis elegans. We have cloned a majority of the Hox genes from the mosquito Anopheles gambiae (Diptera: Culicidae) and compared their genomic organization with that of Tribolium and Drosophila to determine if a split Hox cluster is found in dipterans aside from the Drosophilidae. We find that the Hox genes in Anopheles, as in Tribolium, are organized in a single cluster that spans a genomic region of at least 700 kb. This finding suggests that, within the insect genome, the partition of the Hox cluster may have evolved exclusively within the Drosophila lineage. The genomic structures of the resident genes, however, appear to be largely conserved between A. gambiae and D. melanogaster.

Amino Acid Sequence↗
PubMedDate not supplied

The Rift Valley complex as a barrier to gene flow for Anopheles gambiae in Kenya.

Recent studies of Anopheles gambiae, the principal mosquito vector of malaria in Africa, suggested that the eastern Rift Valley and its surrounding areas act as a barrier to gene flow. To quantify the unique effect of these areas on gene flow, we measured genetic variation within and between populations from each side of the Rift. Low differentiation was measured between populations on each side of the Rift (mean FST < 0.008, mean RST < 0.002). However, high differentiation was measured across the Rift (mean FST = 0.104; mean RST = 0.032). Genetic diversity within populations was lower in eastern populations, suggesting that the effective population sizes (Ne) of these populations were lower than those of western populations. We partitioned the overall differentiation across the Rift into three factors: variation in Ne between populations contributed 7-20%; distance contributed 10-30%, and the remainder, corresponding to the unique effect of the Rift was 50-80%. The Rift's effect was highly significant based on FST. The greater sensitivity of FST in measuring differentiation indicated that drift and not mutation generated the differences between populations. Restricted gene exchange across several hundred kilometers on the face of intense human transportation implies that active mosquito dispersal is the major form of migration, and that migration is a multistep process, where step length is relatively short.

Animals↗
PubMedDate not supplied

Mosaic: a position-effect variegation eye-color mutant in the mosquito Anopheles gambiae.

The Mosaic (Mos) mutation, isolated in the F1 of 60Co-irradiated mosquitoes, confers variegated eye color to third and fourth instar larvae, pupae, and adults of the mosquito Anopheles gambiae. Mos is recessive in wild pink eye (p+) individuals, but is dominant and confers areas of wild-type pigment in mutant pink eye backgrounds. Mos is located 14.4 cM from pink eye on the X chromosome and is associated with a duplication of division 2B euchromatin that has been inserted into division 6 heterochromatin. Various combinations of Mos, pink eye alleles, and the autosomal mutation red eye were produced. In all cases, the darker pigmented regions of the eye in Mos individuals show the phenotypic interactions expected if the phenotype of those regions is due to expression of a p+ allele. Expression of Mos is suppressed by rearing larvae at 32 degrees C relative to 22 degrees C. All of these characteristics are consistent with Mos being a duplicated wild copy of the pink eye gene undergoing position-effect variegation.

Animals↗
PubMedDate not supplied

The Rift Valley complex as a barrier to gene flow for Anopheles gambiae in Kenya: the mtDNA perspective.

Descriptions of A. gambiae population structure based on microsatellite loci and mitochondrial DNA (mtDNA) were incongruent. High differentiation of populations was measured across the Rift Valley by microsatellites, but no differentiation was detected based on mtDNA. To resolve this conflict, we compared the old data to new mtDNA data using the same specimen previously genotyped in microsatellite loci. Analysis of a larger number of mtDNA sequences resulted in high and significant differentiation between populations across the Rift Valley. We developed a method to assess whether differentiation across the Rift Valley was generated by pure drift rather than mutation-drift, based on DNA sequence data. Applying this method to the mtDNA data suggested that pure drift was the primary force generating differentiation between the populations across the Rift, while mutation-drift generated differentiation across the continent. Given adequate sample size, mtDNA provided congruent results with microsatellite loci.

Animals↗
PubMedDate not supplied

Maintenance of chromosome arm integrity between two Anopheles mosquito subgenera.

Low-resolution chromosomal homology between Anopheles gambiae and A. albimanus was determined by polytene chromosome in situ cross hybridization of 17 recombinant DNA and PCR products hybridizing to 23 loci. Hybridization results reflect that the chromosomes have rearranged in the form of autosomal whole-arm translocations and numerous paracentric inversions and not by large detectable pericentric inversions or partial arm translocations. An. gambiae and An. albimanus chromosomes hence differ from each other by possessing alternative autosomal arm associations and rearranged internal structure of each arm, but the integrity of the whole arms has remained conserved. In addition, a photomap of the larval salivary gland polytene chromosomes of An. albimanus that we used to identify sites of hybridization in this species is presented that delineates further banding details than maps published in the past.

Animals↗
PubMedDate not supplied

Genetic traits of the mosquito Anopheles gambiae: red stripe, frizzled, and homochromy1.

The expression, inheritance, and linkage relationships of three genetic traits were studied in the malaria vector Anopheles gambiae. Red stripe (Rs) is a common phenotypic polymorphism in numerous A. gambiae populations, whereas frizzled (f) and homochromy1 (hom1) were isolated from (60)Co-irradiated mosquitoes. Red stripe appears as a diffuse stripe of pigment on the dorsum of larvae and pupae and is variable in expressivity and penetrance. Our data demonstrate that Red stripe results from a heterozygous collarless genotype (i.e., c+ c, chromosome 2) and is essentially sex-limited to females. frizzled is a sex-linked recessive semi-lethal identified by deformed lateral larval setae; its lethality manifests as low rates of adult emergence and brief adult survival. frizzled is located on the X chromosome between pink eye and Mosaic, 3 cM from Mosaic and approximately 12 cM from pink eye. Finally, the mutation homochromy1 (hom1) is on chromosome 2 and causes a recessive phenotype that prevents normal darkening of larvae when reared in a black container. Unlike mutants with this characteristic described thus far, the eye color of hom1 mutants is normal. We determined that hom1 is located between Dieldrin resistance and collarless, approximately 3 cM from the latter. We discuss the possibility of differences in male and female recombination values and the range of values that have been observed in test crosses for chromosome 2 markers.

Alleles↗
PubMedDate not supplied

Eye pigments in wild-type and eye-color mutant strains of the African malaria vector Anopheles gambiae.

Chromatographic analysis of pigments extracted from wild-type eyes of the mosquito Anopheles gambiae reveals the presence of the ommatin precursor 3-hydroxykynurenine, its transamination derivative xanthurenic acid, and a dark, red-brown pigment spot that probably is composed of two or more low mobility xanthommatins. No colored or fluorescent pteridines are evident. Mosquitoes homozygous for an autosomal recessive mutation at the red-eye (r) locus have a brick-red eye color in larvae, pupae, and young adults, in contrast to the almost black color of the wild eye. Mosquitoes homozygous for this mutant allele have levels of ommochrome precursors that are indistinguishable from the wild-type, but the low-mobility xanthommatin spot is ochre-brown in color rather than red-brown as in the wild-type. Mosquitoes with two different mutant alleles at the X-linked pink-eye locus (p, which confers a pink eye color, and pw, which confers a white eye phenotype in homozygotes or hemizygous males) have normal levels of ommochrome precursors but no detectable xanthommatins. Mosquitoes homozygous for both the r and p mutant alleles have apricot-colored eyes and show no detectable xanthommatins. Both the pink-eye and red-eye mutations appear to involve defects in the transport into or assembly of pigments in the membrane-bound pigment granules rather then defects in ommochrome synthesis.

Animals↗
PubMedDate not supplied

Ribosomal DNA-probes differentiate five cryptic species in the Anopheles gambiae complex.

This study describes the use of ribosomal DNA probes to identify the species of individual mosquitoes in the Anopheles gambiae complex, a group of six morphologically identical mosquito species among which are two of the principal vectors of malaria in Africa. The DNA probes are sequences of DNA derived from the ribosomal genes of An. gambiae. Each probe reveals a different sized restriction enzyme fragment specific to each of the five species in the complex that were examined in this study: An. gambiae, An. arabiensis, An. quadriannulatus, An. melas and An. merus. The probes detect highly repeated sequences of DNA, thus the method is sufficiently sensitive to be applied to a small portion of a mosquito. Furthermore, because the DNA can be extracted from desiccated or alcohol preserved specimens, the test is compatible with other mosquito assays performed on dried specimens such as blood meal and malaria sporozoite antigen ELISAs. Determination of the nucleotide sequences that underlie the species-specific restriction enzyme site differences detected by these probes will lead to the development of synthetic DNA probes that can be used to identify an individual mosquito to species on the basis of a simple dot-blot or squash-blot.

Animals↗