Population genetic structure and demography analysis in palinurus elephas populations from atlantic and mediterranean waters

Report for the scientific sojourn at the University of Reading, United Kingdom, from January until May 2008. The main objectives have been firstly to infer population structure and parameters in demographic models using a total of 13 microsatellite loci for genotyping approximately 30 individuals per population in 10 Palinurus elephas populations both from Mediterranean and Atlantic waters. Secondly, developing statistical methods to identify discrepant loci, possibly under selection and implement those methods using the R software environment. It is important to consider that the calculation of the probability distribution of the demographic and mutational parameters for a full genetic data set is numerically difficult for complex demographic history (Stephens 2003). The Approximate Bayesian Computation (ABC), based on summary statistics to infer posterior distributions of variable parameters without explicit likelihood calculations, can surmount this difficulty. This would allow to gather information on different demographic prior values (i.e. effective population sizes, migration rate, microsatellite mutation rate, mutational processes) and assay the sensitivity of inferences to demographic priors by assuming different priors.

Parasitic diseases: opportunities and challenges in the 21st century

The opportunities and challenges for the study and control of parasitic diseases in the 21st century are both exciting and daunting. Based on the contributions from this field over the last part of the 20th century, we should expect new biologic concepts will continue to come from this discipline to enrich the general area of biomedical research. The general nature of such a broad category of infections is difficult to distill, but they often depend on well-orchestrated, complex life cycles and they often involve chronic, relatively well-balanced host/parasite relationships. Such characteristics force biological systems to their limits, and this may be why studies of these diseases have made fundamental contributions to molecular biology, cell biology and immunology. However, if these findings are to continue apace, parasitologists must capitalize on the new findings being generated though genomics, bioinformatics, proteomics, and genetic manipulations of both host and parasite. Furthermore, they must do so based on sound biological insights and the use of hypothesis-driven studies of these complex systems. A major challenge over the next century will be to capitalize on these new findings and translate them into successful, sustainable strategies for control, elimination and eradication of the parasitic diseases that pose major public health threats to the physical and cognitive development and health of so many people worldwide.

Paleoparasitology and the antiquity of human host-parasite relationships

Paleoparasitology may be developed as a new tool to parasite evolution studies. DNA sequences dated thousand years ago, recovered from archaeological material, means the possibility to study parasite-host relationship coevolution through time. Together with tracing parasite-host dispersion throughout the continents, paleoparasitology points to the interesting field of evolution at the molecular level. In this paper a brief history of paleoparasitology is traced, pointing to the new perspectives opened by the recent techniques introduced.

Genetic variability among populations of Lutzomyia (Psathyromyia) shannoni (Dyar 1929) (Diptera: Psychodidae: Phlebotominae) in Colombia

Polyacrylamide gel electrophoresis was used to elucidate genetic variation at 13 isozyme loci among forest populations of Lutzomyia shannoni from three widely separated locations in Colombia: Palambí (Nariño Department), Cimitarra (Santander Department) and Chinácota (Norte de Santander Department). These samples were compared with a laboratory colony originating from the Magdalena Valley in Central Colombia. The mean heterozygosity ranged from 16 to 22%, with 2.1 to 2.6 alleles detected per locus. Nei's genetic distances among populations were low, ranging from 0.011 to 0.049. The estimated number of migrants (Nm=3.8) based on Wright's F-Statistic, F ST, indicated low levels of gene flow among Lu. shannoni forest populations. This low level of migration indicates that the spread of stomatitis virus occurs via infected host, not by infected insect. In the colony sample of 79 individuals, the Gpi locus was homozygotic (0.62/0.62) in all females and heterozygotic (0.62/0.72) in all males. Although this phenomenon is probably a consequence of colonization, it indicates that Gpi is linked to a sex determining locus.

Usefulness of microsatellite typing in population genetic studies of Trypanosoma cruzi

Through microsatellite analysis of 53 monoclonal populations of Trypanosoma cruzi, we found a remarkable degree of genetic polymorphism with no single multilocus genotype being observed more than once. The microsatellite profile proved to be stable during 70 generations of the CL Brener clone in culture. The microsatellite profiling presented also high diagnostic sensitivity since DNA amplifications could be achieved with less than 100 fg DNA, corresponding to half parasite total DNA content. Based on these technical attributes the microsatellite assay turns out to be an important tool for direct typing T. cruzi in biological samples. By using this approach we were able to type T. cruzi in feces of artificially infected bugs and in single cells sorted by FACS. The microsatellites have shown to be excellent markers for T. cruzi phylogenetic reconstruction. We used maximum parsimony based on the minimum number of mutational steps to build an unrooted Wagner network, which confirms previous conclusions based on the analysis of the D7 domain of the LSU rDNA gene that T. cruzi is composed by two major groups. We also obtained evidence that strains belonging to rRNA group 2 are subdivided into two genetically distant clusters, and that one of these clusters is more related to rRNA group 1/2. These results suggest different origins for these strains.

Genetic markers from Biomphalaria tenagophila (Gastropoda: Pulmonata: Planorbidae) obtained by the double stringency polymerase chain reaction technique

Biomphalaria tenagophila, one of the intermediate hosts of the trematoda Schistosoma mansoni, is a simultaneous hermafrodite snail species. In order to analyse the genetic structure of these populations, we performed a double-stringency PCR technique to obtain genetic markers with microsatellites and arbitrary primers in a single reaction.

View of Clinical Genetic Services in Northern Ireland - Equality Impact Assessment (PDF 306 KB)

Public Consultation on the Future Development of Clinical Genetic Services - Part II (Equality Impact Assessment)

Future Development of Clinical Genetic Services (PDF 284 KB)

Public Consultation on the Future Development of Clinical Genetic Services - Part I

Isoenzyme profiles of Trypanosoma cruzi stocks from different areas of Paraguay

Twenty one Trypanosoma cruzi stocks from humans, domiciliary triatomines and one sylvatic animal of different areas of Paraguay were subjected to isoenzyme analysis. Thirteen enzyme systems (15 loci in total) were studied. MN cl2 (clonets 39) and SO34 cl4 (clonets 20) were used as references. Relationships between stocks were depicted by an UPGMA dendrogram constructed using the Jaccard´s distances matrix. Among the Paraguayan stocks 14 zymodemes were identified (Par1 to Par14), Par 5 being the most frequent. Polymorphism rate and clonal diversity were 0.73 and 0.93, respectively. Average number of alleles per polymorphic locus was 2.5 (range 2-4). These measurements show a high diversity, which is confirmed by the dendrogram topology. All stocks belong to the same lineage, as MN cl2 reference strain (T. cruzi II). Moreover three distinct subgroups were identified and two of them correspond to Brazilian and Bolivian zymodemes, respectively. The third subgroup, the most common in Paraguay, is related to Tulahuen stock. The large geographical distribution of some zymodemes agrees with the hypothesis of clonality for T. cruzi populations. However sample size was not adequate to detect genetic recombination in any single locality.

Genetic variability in Brazilian populations of Biomphalaria straminea complex detected by simple sequence repeat anchored polymerase chain reaction amplification

Biomphalaria glabrata, B. tenagophila and B. straminea are intermediate hosts of Schistosoma mansoni, in Brazil. The latter is of epidemiological importance in the northwest of Brazil and, due to morphological similarities, has been grouped with B. intermedia and B. kuhniana in a complex named B. straminea. In the current work, we have standardized the simple sequence repeat anchored polymerase chain reaction (SSR-PCR) technique, using the primers (CA)8RY and K7, to study the genetic variability of these species. The similarity level was calculated using the Dice coefficient and genetic distance using the Nei and Li coefficient. The trees were obtained by the UPGMA and neighbor-joining methods. We have observed that the most related individuals belong to the same species and locality and that individuals from different localities, but of the same species, present clear heterogeneity. The trees generated using both methods showed similar topologies. The SSR-PCR technique was shown to be very efficient in intrapopulational and intraspecific studies of the B. straminea complex snails.

Quantification, self-renewal, and genetic tracing of FL1+ tumor-initiating cells in a large cohort of human gliomas.

Evidence has emerged that the initiation and growth of gliomas is sustained by a subpopulation of cancer-initiating cells (CICs). Because of the difficulty of using markers to tag CICs in gliomas, we have previously exploited more robust phenotypic characteristics, including a specific morphology and intrincic autofluorescence, to identify and isolate a subpopulation of glioma CICs, called FL1(+). The objective of this study was to further validate our method in a large cohort of human glioma and a mouse model of glioma. Seventy-four human gliomas of all grades and the GFAP-V(12)HA-ras B8 mouse model were analyzed for in vitro self-renewal capacity and their content of FL1(+). Nonneoplastic brain tissue and embryonic mouse brain were used as control. Genetic traceability along passages was assessed with microsatellite analysis. We found that FL1(+) cells from low-grade gliomas and from control nonneoplasic brain tissue show a lower level of autofluorescence and undergo a restricted number of cell divisions before dying in culture. In contrast, we found that FL1(+) cells derived from many but not all high-grade gliomas acquire high levels of autofluorescence and can be propagated in long-term cultures. Moreover, FL1(+) cells show a remarkable traceability over time in vitro and in vivo. Our results show that FL1(+) cells can be found in all specimens of a large cohort of human gliomas of different grades and in a model of genetically induced mouse glioma as well as nonneoplastic brain. However, their self-renewal capacity is variable and seems to be dependent on the tumor grade.

Differentiation and genetic analysis of Rhodnius prolixus and Rhodnius colombiensis by rDNA and RAPD amplification

Domiciliated Rhodnius prolixus and sylvatic R. colombiensis were analyzed in order to confirm their genetic divergence and verify the risk that the latter represents in the domiciliation process, and to provide tools for identifying the sources of possible reinfestation by triatomines in human dwellings allowing control programs to be undertaken. Comparison of random amplified polymorphic DNA amplification patterns and cluster analysis suggests reproductive discontinuity between the two species. The calculated statistical F value of 0.24 and effective migration rate of 0.6 individuals per generation are insufficient to maintain genetic homogeneity between them and confirm the absence of present genetic flow. R. colombiensis presents higher intrapopulation variability. Polymerase chain reaction of ribosomal DNA supports these findings. The low genetic flow between the two species implies that R. colombiensis do not represent an epidemiological risk for the domiciliary transmission of Trypanosoma cruzi in the Tolima Department. The lower variability of the domiciliated R. prolixus could result in greater susceptibility to the use of pesticides in control programs.