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S J Kemp

Publications and source records attributed to S J Kemp.

At least 19 recordsLinked to original sources
PubMed2003

Genetic identification of two sibling species of Lutzomyia longipalpis (Diptera: Psychodidae) that produce distinct male sex pheromones in Sobral, Ceará State, Brazil.

Lutzomyia longipalpis, the main sandfly vector for New World visceral leishmaniasis is a complex of an as yet undefined number of sibling species. At present, there is no consensus on the status (single species vs. species complex) of Brazilian populations. We applied five microsatellite loci to test the hypothesis that L. longipalpis occurs as two sympatric cryptic species in Sobral, Ceará State, Brazil as predicted by male sex pheromone chemotypes described previously for field specimens from this site [S-9-methyl-germacrene-B (9MGB) and a cembrene compound]. Abdominal spot morphology corresponds with pheromone type at this locality (9MGB in '1 spot' males and cembrene in '2 spot' males). Genotype data from 190 wild-caught L. longipalpis specimens collected in October 1999 and April 2001 were used to estimate genetic differentiation between the two sex pheromone populations and sampling dates. No significant (P > 0.05) genetic differences were found between the 1999 and 2001 9MGB samples (theta = 0.018; RST = -0.005), and genetic differentiation was low between the cembrene collections (theta = 0.037, P < 0.05; RST = -0.043, P > 0.05). By contrast, highly divergent allelic frequencies (largely at two microsatellite loci) corresponded to significant (P > 0.05) genetic differentiation (theta = 0.221; RST = 0.215) for all comparisons between samples with different pheromones. When pheromone samples were pooled across sample date, genetic differentiation was high (theta = 0.229; P < 0.001; Nem = 0.84). The allele frequency distribution at each of the five microsatellite loci was similar for males and females from the two collection years. Two of these loci showed highly divergent allele frequencies in the two sex pheromone populations. This was reflected in the highly significant genetic differentiation obtained from the male genotypes, between populations producing different pheromones (theta = 0.229-0.268; P < 0.0001 for the 2001 and theta = 0.254-0.558; P < 0.0001 for the 1999 collections, respectively). Similar results were obtained when the females, assigned to a pheromone type, were included in the analysis. Both a Bayesian analysis of the data set and a population assignment test provided strong evidence for two distinct populations corresponding to pheromone type. Given its genotype, the probability of assigning a 9MGB male to the original 9MGB population was 100% once the two years' collections were pooled. For cembrene-producing '2 spot' males this probability although still high, was lower than for 9MGB males, at 86%. This microsatellite data together with previously reported reproductive isolation between the two Sobral populations confirm that premating barriers are important in speciation of L. longipalpis.

Animals↗
PubMed2002

Host specificity of Trypanosoma (Herpetosoma) species: evidence that bank voles (Clethrionomys glareolus) carry only one T. (H.) evotomys 18S rRNA genotype but wood mice (Apodemus sylvaticus) carry at least two polyphyletic parasites.

The strongest evidence for host specificity of mammalian trypanosomes comes from parasites of the subgenus Trypanosoma (Herpetosoma). Laboratory studies have shown that T. (Herpetosoma) species will not infect an alternative host. However, this has not been demonstrated in wild populations. We screened 560 bank voles (Clethrionomys glareolus) and 148 wood mice (Apodemus sylvaticus) for trypanosomes by PCR amplification of the 18S rRNA gene. In total, 109 (19%) bank voles and 12 (8%) wood mice were infected. A HaeIII restriction site was discovered that could be used to discriminate between T. (H.) evotomys of the bank vole and T. (H.) grosi of the wood mouse. All the parasites in the bank voles were identified as T. (Herpetosoma) evotomys by RFLP-PCR. Out of the 12 wood mouse infections 10 were due to T. grosi. Two of the wood mice were infected with parasites with a novel genotype that was most similar to those of T. evotomys and T. microti of voles. Fifty-six fleas collected from the rodents were also screened for trypanosomes; 9 were infected with T. evotomys and 1 with T. grosi. One of the fleas infected with T. evotomys was collected from a wood mouse.

Animals↗
PubMed2002

Towards a standard battery of microsatellite markers for the analysis of the Leishmania donovani complex.

The investigation of microsatellite markers has recently superseded that of isoenzymes for many population-biology applications. Microsatellites have the advantages of being dominant, neutral, highly polymorphic and easily scored by high-throughput methods. However, it is necessary to develop a new panel of markers for each group of organisms of interest. Previously, only about 5% of the markers that amplify Leishmania major microsatellite loci were also found to amplify L. donovani loci. A panel of 20 microsatellite markers that are polymorphic in L. donovani and L. infantum has now been developed, using a rapid-enrichment method that will be suitable for developing libraries of markers for other trypanosomatid species. This is the first panel of polymorphic microsatellite markers, to be isolated de novo from any species of Leishmania, that is large enough for population-biology applications.

Alleles↗
PubMed2001

Copper toxicosis in the Bedlington terrier: a diagnostic dilemma.

Diagnosis of copper toxicosis (CT) in Bedlington terriers by the quantitative and qualitative assessment of copper (Cu) in, and pathology of, biopsies has been largely superseded by a DNA-based assay which uses a microsatellite marker (C04107) linked to the CT disease allele. A retrospective study was conducted comprising 154 liver biopsies from Bedlington terriers with 22 matched DNA markers to compare the two methods in the diagnosis of CT. For the biopsy method, three categories (phenotypes) were identified based on analytical and morphological criteria: 'unaffected' in 83 samples (54 per cent), where Cu was much less than 400 microg/g, and there was an absence of visual Cu or liver damage; 'intermediate' in 18 samples (12 per cent), where Cu was less than 400 microg/g, and there was limited histochemical Cu and no/equivocal damage; and 'affected' in 53 samples (34 per cent), where Cu was greater than 400 microg/g, there was histochemical Cu and liver damage was poorly related to Cu content. In the DNA assay, which was used alone on unrelated individuals, the microsatellite marker failed to identify the CT status of any of the groups. Liver biopsy remains a reliable indicator of Cu accumulation and progressive liver disease in individual dogs. The microsatellite marker C04107 has a predictive value only when supported by a pedigree.

Animals↗
PubMed2000

Fine mapping of trypanosomiasis resistance loci in murine advanced intercross lines.

We have previously reported the results of genome-wide searches in two murine F(2) populations for QTLs that influence survival following Trypanosoma congolense infection. Three loci, Tir1, Tir2, and Tir3, were identified and mapped to mouse Chromosomes (Chrs) 17, 5, and 1 respectively, with confidence intervals (CIs) in the range 10-40 cM. The size of these CIs is to a large degree the consequence of limited numbers of recombination events in small chromosomal regions in F(2) populations. A number of population designs have been proposed to increase recombination levels in crosses, one of which is the advanced intercross line (AIL). Here we report fine mapping of Tir1, Tir2, and Tir3 in G6 populations of two independent murine AILs created by crossing the C57BL/6J strain with the A/J and BALB/cJ strains, respectively. Data were analyzed by two methods that gave equally informative and similar results. The three QTLs were confirmed in the A/J x C57BL/6J AIL and in the combined data set, but Tir2 was apparently lost from the BALB/cJ x C57BL/6J AIL. The reduction in CIs for the Tir loci ranged from 2.5 to more than ten-fold in G6 populations by comparison with CIs obtained previously in the equivalent F(2) generations. Mapping in the AILs also resolved the Tir3 locus into three trypanosomiasis resistance QTLs, revealing a degree of complexity not evident in extensive studies at the F(2) level.

Animals↗
PubMed2000

Evidence for genomic imprinting of the major QTL controlling susceptibility to trypanosomiasis in mice.

Inbred strains of laboratory mice exhibit marked differences in survival time following infection with Trypanosoma congolense, the principal cause of trypanosomiasis in African livestock. The difference in survival time between the relatively resistant C57BL/6 J and more susceptible BALB/c inbred strains has been attributed to three quantitative trait loci (QTLs), Tir1, Tir2 and Tir3. In order to determine whether there was a parent-of-origin effect on this trait, four backcross populations derived from the C57BL/6 J and BALB/c parental strains were bred and inoculated with T. congolense. The two populations with F1 fathers and BALB/c mothers had a significantly greater overall survival rate than the two populations with BALB/c fathers and F1 mothers. This pattern of inheritance suggested the involvement of imprinted genes. Genotyping with markers at the three QTLs controlling susceptibility revealed that the difference in survival time was consistent with genomic imprinting of the QTL of largest effect, Tir1.

Animals↗
PubMed1998

Report of the first workshop on the genetic map of bovine chromosome 1.

A report of the first workshop on the genetic map of bovine chromosome 1 (BTA1) is presented. Five laboratories contributed 31,962 informative meioses from 70 loci. Thirty-two loci which had been typed by at least two laboratories were used to construct a framework genetic map with a likelihood ratio support of at least 1000:1 for locus order. The resulting sex-averaged framework map contained 26 loci and spanned 163.6 CM. The lengths of the female and male maps were 159.5 CM and 165.3 CM, respectively, and there was evidence for an expansion in the telomeric one-third of the male map. Of the four cases where order for closely linked loci differed among the maps produced for each of the contributing laboratories, a consensus order was obtained for three in the framework map. The average genetic distance between framework loci on the sex-averaged map was 6.3 CM.

Animals↗
PubMed1997

A medium-density genetic linkage map of the bovine genome.

A cattle genetic linkage map was constructed which covers more than 95 percent of the bovine genome at medium density. Seven hundred and forty six DNA polymorphisms were genotyped in cattle families which comprise 347 individuals in full sibling pedigrees. Seven hundred and three of the loci are linked to at least one other locus. All linkage groups are assigned to chromosomes, and all are orientated with regards to the centromere. There is little overall difference in the lengths of the bull and cow linkage maps although there are individual differences between maps of chromosomes. One hundred and sixty polymorphisms are in or near genes, and the resultant genome-wide comparative analyses indicate that while there is greater conservation of synteny between cattle and humans compared with mice, the conservation of gene order between cattle and humans is much less than would be expected from the conservation of synteny. This map provides a basis for high-resolution mapping of the bovine genome with physical resources such as Yeast and Bacterial Artificial Chromosomes as well as providing the underpinning for the interpolation of information from the Human Genome Project.

Animals↗
PubMed1997

Sensitivity of segregation analysis to data structure and transformation: a case study of trypanotolerance in mice.

Sensitivity of segregation analysis for data structure and data transformation was studied using data from two trials in which mice were challenged at three months of age with a cloned isolate of Trypanosoma congolense and survival time was recorded. Data included records from three inbred strains (C57BL/6 (tolerant), A/J, and BALB/c (both susceptible)) and their crosses. Data were standardized and normalized using a modified power transformation. Segregation analysis was applied to both untransformed and transformed data to determine the genetic inheritance of trypanotolerance in these mice. Data from the two trials were analysed separately and combined. Four genetic models were compared; a one locus model, a polygenic model, a mixed model with common variance, and a mixed model with different variances for each major genotype. Even though the separate data sets and the combined data set all supported the hypothesis of a major gene (or a tightly linked cluster of genes) with different variances within each genotype, parameter estimates were highly sensitive to data transformation and several sets of parameter estimates gave similar likelihood values because of high dependency between parameters. Based on the results segregation analysis can be very sensitive to data structure in a crossbreeding design and to data transformation. Interpretation of the results can be misleading if the entire parameter space is not studied carefully.

Animals↗
PubMed1997

Localization of genes controlling resistance to trypanosomiasis in mice.

Tsetse fly-transmitted trypanosomes (Trypanosoma spp.) cause "sleeping sickness' in man and have a serious impact on livestock-based agriculture in large areas of Africa. Multigene control of variation in susceptibility to trypanosomiasis is known to occur in mice, where the C57BI/6 (B6) strain is relatively resistant and the A/J (A) and Balb/c (B) strains are susceptible. Such resistance is also well described among several types of west African cattle. We report here the results of genome-wide scans for genes controlling this trait in the B6 mouse using crosses with two different susceptible strains. Regions on mouse chromosomes 5 and 17 were found to be important in determining resistance in both crosses while an additional region on chromosome 1 showed evidence of involvement in only one cross. We confirmed the size of the effect due to chromosome 17 in F3 intercross populations fixed for alternative parental chromosomes. The three loci are of large effect and account for most of the genetic variation in both F2 populations. We propose that they be designated Tir1, Tir2 and Tir3.

Animals↗
PubMed1996

Involvement of protein tyrosine kinases in regulation of endothelial cell organization by basement membrane proteins.

During capillary formation, endothelial cell migration and organization are critically dependent on surrounding basement membrane proteins. These proteins serve as a physical support and are likely to provide signals which regulate migration and organization of the cells. In this study the possible involvement of tyrosine kinase signalling pathways in basement membrane-induced organization of human endothelial cells is examined. Interaction of endothelial cells with reconstituted basement membrane Matrigel activates tyrosine phosphorylation of several proteins including focal adhesion kinase. Inhibition of this pathway with tyrosine kinase inhibitors impairs localization of paxillin to focal adhesions and organization of actin filaments, decreases motility and elongation of endothelial cells, and prevents their organization into cords or tubes on basement membrane. These data demonstrate that basement membrane-induced modulation of endothelial cell motility, shape, and organization is critically dependent on tyrosine kinase signalling pathway(s) involving cytoskeletal proteins.

Basement Membrane↗
PubMed1996

Polymorphism at the bovine tumor necrosis factor alpha locus and assignment to BTA 23.

We have identified four single-strand conformation variants of the bovine tumor necrosis factor alpha gene by analysis of PCR-amplified fragments. The variants are inherited in Mendelian fashion and are informative for linkage mapping. We have mapped the bovine gene to Chromosome (Chr) 23 in a panel of somatic cell hybrids and observed genetic linkage to the major histocompatibility complex (BoLA) genes and microsatellite markers on bovine Chr 23 in an international bovine reference family panel. The distribution of the alleles was determined in cattle of different breeds and of different geographical origins, which included trypano-susceptible and trypano-tolerant cattle.

Animals↗
PubMed1996

Genetic control of resistance to trypanosomiasis.

To map the genetic sources of trypanotolerance in mice, a linkage analysis of survival following trypanosome challenge was performed by selective genotyping in a large F2 population produced by crossing the resistant C57BL/6 and susceptible BALB/c inbred mouse lines. We report evidence of a chromosomal region of large effect, possibly comprising more than one resistance locus, on Chromosome 17; and of further loci on Chromosomes 1 and 5. Together, these genes can account for all of the difference between the mean parental phenotypes.

Animals↗
PubMed1995

Parasite strain specificity of bovine cytotoxic T cell responses to Theileria parva is determined primarily by immunodominance.

The parasite strain specificity of CTL responses to Theileria parva varies among cattle immunized with the same parasite stock. We have investigated the influence of class I MHC on the strain specificity of CTL responses to T. parva in 19 cattle of defined class I phenotype immunized with either of two T. parva populations, in which protection to subsequent reciprocal challenge correlated with CTL strain specificity. In the majority of animals the response was restricted by the products of one MHC haplotype and there was a consistent bias to some haplotypes in preference to others. In 10 of 13 cattle expressing the molecularly defined MHC specificities A10 and KN104 on one haplotype, the CTL response was restricted entirely by this haplotype, thus allowing a precise analysis of the MHC restriction specificities. The MHC restriction specificity and the parasite population used for immunization both influenced the strain specificity of the response. By examining responses in identical twins immunized with different parasites or in animals before and after challenge with heterologous parasites, animals that mounted a strain-specific response to primary infection were shown to be capable of responding to Ags shared by the two parasite populations. These findings indicate that the strain specificity of CTL responses to T. parva is not determined primarily by immune response genes that define the inherent capacity to respond, but rather is a consequence of the response in individual animals being biased toward a limited number of immunodominant peptide-MHC determinants.

Animals↗