Search PubMed⌕ Search

Biomedical subjects

F H Collins

Publications and source records attributed to F H Collins.

At least 73 records · Page 4Linked to original sources
PubMed1995

Evolution of the rDNA spacer, ITS 2, in the ticks Ixodes scapularis and I. pacificus (Acari: Ixodidae).

Evolution of the rDNA spacer, ITS 2, is examined by comparing 17 DNA sequences of the ticks, Ixodes scapularis and I. pacificus. The distribution of fixed interspecific differences and the relative frequency of base changes vs. insertions/deletions (indels) matches the distribution and relative frequency for intraspecifically variable sites. This suggests that most intraspecific variation is not effectively selected against. The base composition of the ITS 2 transcript is G- and U-biased. But, 5-base regions enriched (> 80 per cent) for A or U occur more frequently than expected while G- and C-enriched regions occur less frequently than expected. Enriched sequences may be prone to replication slippage, accounting for the A/T bias in insertions. Slippage-mediated gains and losses of A/T-rich tandem repeats apparently account for most indels. Minimum-energy conformations of the two species' folded transcripts share major structural features. Structural inertia arises from intramolecular base pairing within stems that allows most mutations to be absorbed as new bulges off stems. Yet, there is evidence of selection to maintain the conformation. First, intraspecifically variable sites are concentrated at the ends of stems in loops and intersections, structures that do not contribute to intramolecular base pairing. Moreover, some indels that have become fixed in one species compensate for the presence of conformation-destabilizing indels. However, high rates of sequence evolution within stems and absence of compensatory base evolution contraindicates selective constraint. Degenerate dispersed and tandem copies of two subrepeats, each approximately 20 bases long, may account for much of the ITS 2 sequence. These are approximately inverses of each other and are, consequently, capable of significant intramolecular hydrogen bonding to produce folded transcripts of low energy. Evolution of the ITS 2 sequence may largely entail replication slippage-mediated gains and losses of these repeats or their composite subrepeats.

Animals↗
PubMed1995

Variation in ribosomal DNA internal transcribed spacers 1 among eastern populations of Ixodes scapularis (Acari: Ixodidae).

The base sequence of the internal transcribed spacer 1 (ITS 1) of ribosomal DNA of the tick Ixodes scapularis Say (= I. dammini Spielman, Clifford, Piesman & Corwin) was determined to assess genetic divergence between populations along the eastern (Atlantic) seaboard of the United States. Twenty sequences were obtained from localities down the eastern margin of the species's range: 10 from the southeast (Georgia and Florida), seven from the middle east (North Carolina, Maryland), and three from the northeast (Massachusetts, New Jersey, New York). Both the neighbor-joining and parsimony methods cluster most of the southeastern sequences together and most of the middle eastern sequences together but fail to cluster those from the northeast. In addition, an F ratio test revealed significant between-region sequence variation. Thus, there appears to be genetic structuring on at least a macrogeographic scale. Only 23% (SEM = 6.4%) of the sequence variation occurs between regions, with the vast majority of variation, 77% (SEM = 6.4%), being within region. These data, plus other published data, indicate that I. scapularis constitutes a single species. However, the pattern of variation is consistent with restricted gene flow between regions or, alternatively, with recent introgression between northern and southern types in the middle-eastern part of the species's range.

Animals↗
PubMed1995

Cloning and characterization of the white gene from Anopheles gambiae.

A 14 kb region of genomic DNA containing the X-linked Anopheles gambiae eye colour gene, white, was cloned and sequenced. Genomic clones containing distinct white+ alleles were polymorphic for the insertion of a small transposable element in intron 3, and differed at 1% of nucleotide positions compared. Sequence was also determined from a rare 2914 bp cDNA. Comparison of cDNA and genomic sequences established an intron-exon structure distinct from Drosophila white. Despite a common trend in Anopheles and Drosophila of weak codon bias given low levels of gene expression, codon usage by Anopheles gambiae white was strongly biased. Overall amino acid identity between the predicted mosquito and fruitfly proteins was 64%, but dropped to 14% at the amino terminus. To correlate phenotypically white-eyed strains of A. gambiae with structural lesions in white, five available strains were analysed by PCR and Southern blotting. Although these strains carried allelic mutations, independently generated by gamma radiation (three strains) or spontaneous events (two strains), no white lesions were detected. Significantly, another non-allelic X-linked mutation, causing an identical white-eyed phenotype, has been correlated with a structural defect in the cloned white gene (Benedict et al., 1995). Taken together, these observations suggest that the white-eyed mutants analysed in the present study carry mutations in a second eye colour gene and are most likely white+.

ATP-Binding Cassette Transporters↗
PubMed1995

Malaria: current and future prospects for control.

Malaria is the most important insect-transmitted human disease, but progress in its control has been slow, especially in Africa where approximately 90% of the infections occur. Several factors have contributed to the problem. Parasites and vectors have developed resistance to antimalarial drugs and insecticides; differences in the biology of major malaria vectors preclude the development of simple, universally applicable strategies for malaria control; and the cost of available malaria-control tools often exceeds the public health resources in the most malarious parts of the world. New tools are desperately needed. Current efforts include the testing of tools such as insecticide-impregnated bed nets that could become available in the near term, as well as long-term projects such as the development of malaria vaccines and mosquito-targeted genetic control strategies. The success or failure of any of these approaches will depend ultimately on understanding the natural patterns of malaria transmission in the field.

Animals↗
PubMed1994

Diversity of cytochrome P450 genes in the mosquito, Anopheles albimanus.

Degenerate oligonucleotide primers were designed for conserved regions of cytochrome P450 proteins of the CYP4 family and were used to amplify cDNA or genomic DNA from different strains of the New World malaria vector, Anopheles albimanus (Weidemann). The PCR products were cloned, sequenced and compared to each other and to members of the P450 family CYP4. Seventeen new P450 genes were identified in five CYP4 subfamilies. Five of the ten PCR products of genomic DNA were shown to contain a short (60-79 bp) intron at the same position as introns in the Drosophila CYP4D2 and CYP4E1 genes.

Amino Acid Sequence↗
PubMed1994

Molecular phylogeny of the Anopheles gambiae complex suggests genetic introgression between principal malaria vectors.

The six Afrotropical species of mosquitoes comprising the Anopheles gambiae complex include the most efficient vectors of malaria in the world as well as a nonvector species. The accepted interpretation of evolutionary relationships among these species is based on chromosomal inversions and suggests that the two principal vectors, A. gambiae and Anopheles arabiensis, are on distant branches of the phylogenetic tree. However, DNA sequence data indicate that these two species are sister taxa and suggest gene flow between them. These results have important implications for malaria control strategies involving the replacement of vector with nonvector populations.

Animals↗
PubMed1994

An Anopheles gambiae cDNA predicts a protein similar to a yeast Suil translation factor.

The nucleotide (nt) sequence of a cDNA cloned from the mosquito Anopheles gambiae was determined. The amino acid (aa) sequence of the deduced protein was 56% identical (60/108 aa) to the recently discovered translation initiation factor Suil of yeast, suggesting that the two proteins are homologs and have similar functions. Database searches also revealed strong similarity to other sequences, including the deduced gene products of cDNAs from organisms as diverse as nematodes, humans and plants. The functions of these putative proteins are unknown, but their homology to Suil suggests that they represent an important component of the eukaryotic translation initiation complex.

Amino Acid Sequence↗
PubMed1994

A cytoskeletal actin gene in the mosquito Anopheles gambiae.

Five actin genes have been identified in the mosquito Anopheles gambiae, and a constitutively expressed actin gene has been chosen for detailed analysis. We have physically mapped and sequenced this gene and six associated cDNAs, including translated coding regions, as well as the 5' and 3' flanking sequences. Analysis of stage-specific RNA shows this gene to be present in all stages of mosquito development and in an established A. gambiae cell line, thus indicating a cytoskeletal actin. In the sequence of the translated coding region and in pattern of expression, this gene is very similar to the cytoskeletal actin genes of Drosophila melanogaster, and in sequence, equally similar to the Artemia cytoskeletal actin gene 403 (99.2% identity among the three amino acid sequences). Sequencing of this A. gambiae actin gene (designated act1D for its location in chromosome division 1D) and selected cDNAs shows that it possesses three alternative leader sequences; thus the gene appears to have three alternative promoters. These promoters should ultimately prove useful in the production of transgenic constructs for constitutive expression.

Actins↗
PubMed1994

A cDNA encoding an ADP/ATP carrier from the mosquito Anopheles gambiae.

Two cDNAs are described from Anopheles gambiae that correspond to the ADP/ATP carrier or translocase. The clones are identical except for minor differences in the 5' non-coding region and in the lengths of the poly-A tails. They code for mRNAs of 1261 and 1263 bp and contain one open reading frame of 906 bp. A probe made from the 1263 bp cDNA hybridized to bands of approximately 1260 and 1700 bp on developmental Northern blots. The putative 300 amino acid peptide sequence shows from 53.4-78.5% identity to AAC peptide sequences from a range of organisms from Zea mays to human. Both clones mapped to region 26a on the left arm of chromosome 2 in An. gambiae.

Amino Acid Sequence↗
PubMed1994

A technique for nucleic acid in situ hybridization to polytene chromosomes of mosquitoes in the Anopheles gambiae complex.

A sensitive, simple, and reproducible in situ hybridization technique for the detection and precise localization of specific nucleic acid sequences on chromosomes of members of the Anopheles gambiae complex is described. Modifications of the in situ hybridization technique are described that allow simultaneous hybridization of several probes with the chromosomes on a single slide and the multiple use of a single chromosome preparation for several different probes hybridized successively on the same slide. Examples are shown that illustrate the utility of the technique for localization of both single copy and repeated sequences in both polytenized euchromatin and centromeric heterochromatin.

Animals↗
PubMed1993

Investigation of the validity of species status of Ixodes dammini (Acari: Ixodidae) using rDNA.

The two internal transcribed spacers (ITS1 and ITS2) of rDNA of three members of the Ixodes ricinus "complex" (Acari: Ixodidae) were sequenced. Sequence variation was assessed for the North American species I. scapularis, I. dammini, and I. pacificus at three levels: within individual/population, between individuals of different geographic origin within a species, and between species. Both spacers are highly variable, particularly with regard to small deletions and additions which may arise via replication slippage. Homogenization of rDNA multigene arrays for particular sequence variants appears to occur at a relatively rapid rate, since I. pacificus sequences differ from the others at numerous invariant sites, facilitating the use of these sequences to assess sibling species relationships. Based on maximum parsimony and two distance methods (unweighted pair-group with arithmetic means and neighbor-joining), sequence variation in ITS1 and ITS2 suggests that I. scapularis and I. dammini are not distinct species and that even individuals from geographically isolated locations are very similar. Individuals from geographically separated populations of I. pacificus appear to be relatively less closely related to each other but distinct from those of I. scapularis/dammini. In I. scapularis/dammini, diversity within and between individuals from geographic populations contributed equally to total sequence diversity.

Animals↗
PubMed1993

A detailed genetic map for the X chromosome of the malaria vector, Anopheles gambiae.

Anopheles gambiae, the primary vector of human malaria in Africa, is responsible for approximately a million deaths per year, mostly of children. Despite its significance in disease transmission, this mosquito has not been studied extensively by genetic or molecular techniques. To facilitate studies on this vector, a genetic map has been developed that covers the X chromosome at an average resolution of 2 centimorgans. This map has been integrated with the chromosome banding pattern and used to localize a recessive, sex-linked mutation (white eye) to within 1 centimorgan of flanking markers.

Alleles↗
PubMed1993

[Comparison of PCR and cytogenetic methods for the identification of mosquito species of the Anopheles gambiae complex in Senegal].

The classical cytological technique and a new PCR technique were compared for the identification of mosquito species of the Anopheles gambiae complex. Fifty seven specimens, caught in three different bioclimatic senegalese regions, were tested. Thirty two An. gambiae and 25 An. arabiensis were determined by both methods. All the results were similar. The advantages of each method are discussed.

Animals↗