| Autor: |
Raadsma, H.W., Margawati, E.T., Spithill, T., Subandriyo, E., Estuningsih, E., Widjayanti, S., Piedrafita, D. |
| Jazyk: |
angličtina |
| Rok vydání: |
2002 |
| Předmět: |
|
| Zdroj: |
Second international symposium on Candidate Genes for Animal Health (C.G.A.H), Montpellier, France, August 16-18th 2002 : abstracts |
| Popis: |
Parasitism by fasciolosis affects cattle and buffalo production throughout the tropical regions in the world with and estimated economic impact of $US2billion/pa. In a unique research strategy we aim to exploit the extreme genetic resistance of the Indonesian Thin Tail (ITT) sheep to undertake molecular characterisation of a putative major gene for Fasciola gigantica (FGR) resistance in these sheep by a combined functional genomics and positional cloning approach, and through comparative mapping, identify homologous genes in cattle and buffalo for commercial application. The strategy for the immunological programme developed in parallel with the genome screen, is to provide function/identity of putative candidate genes through understanding the mechanisms of resistance determined by the FGR gene. This approach is now used in contemporary genome biology as a "functional genomics" approach for gene identification and isolation to open new avenues in genetic control or identification of new regulatory factors for control of internal parasites in ruminants. Our gene mapping approach uses 10 resource families which are a highly heterozygous cross between resistant (ITT) and susceptible (Merino) genotypes. These families are used to create 600 backcross progeny to obtain gene expression in a susceptible (Merino) background. All progeny are being phenotyped for expression of resistance by challenge with 300 viable Fasciola gigantica metacercaria. Following measurement of an extensive range of immunological and haernatological parameters during infection, all sheep are slaughtered at 16 weeks for assessment of parasite parameters (resistance). Preliminary segregation analysis in 400 progeny from 7 sires, supports the presence of a gene with large effect for resistance to F gigantica. A strong sex x major gene interaction was evident, in which males expressed the putative gene, whereas females did not in 4 out of the 5 families in which segregation was evident. The major gene effect was consistent for male progeny groups with approximately a 50% reduction in fluke burden (20-28 flukes). Genome analysis is undertaken in all progeny by a full genome scan using a panel of 85 highly polymorphic micro-satellite markers to obtain a chromosomal location of the putative major gene as the first step in a positional candidate cloning approach. A complete analysis of our first 3 families, revealed a putative QTL in males but not female progeny. Based on a functional assessment of the genetic mechanism for resistance, a fine mapping approach in extended families, and detailed comparative mapping to man, mouse and other ruminant systems, we intend to obtain a positional clone for all major candidate genes as potential FGR resistance genes. Through a novel in-vitro killing assay of juvenile Fasciola parasites, our in vitro studies have demonstrated the effector cells mediating killing of F. gigantica immature parasites include ITT macrophages and eosinophils and the molecular mechanism of killing involves superoxide radicals. Furthermore IgG2 responses correlated with susceptibility to infection. Results from our immunological approach, using in vitro and in vivo experimental approaches, collectively suggests Th1-like responses are associated with the susceptibility of Merino sheep to F. gigantica infection while, conversely, Th2-like responses are associated with the resistance of ITT sheep to F. gigantica infection. (Texte intégral) |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
|
