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I dentification of Quantative Trait L oci (QTL) M odulating Scrapie Incubation Period In SHEEP

I dentification of Quantative Trait L oci (QTL) M odulating Scrapie Incubation Period In SHEEP. Introduction. Scrapie and BSE pose health problems in Livestock production But no treatment is still available. How can we fight scrapie disease ?

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I dentification of Quantative Trait L oci (QTL) M odulating Scrapie Incubation Period In SHEEP

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  1. Identification of Quantative Trait Loci (QTL) Modulating Scrapie Incubation Period In SHEEP Toulouse IWMGQSG dec 2003

  2. Introduction • Scrapie and BSE pose health problems in Livestock production But no treatment is still available How can we fightscrapie disease? In sheep, a genetic approach is used : selection on resistant PrP allele. Why is it useful to look for other loci than PrP in sheep? 1) To obtain other genes to select on resistance in sheep (and in cattle) 2) To better understand mechanisms of prion diseases Toulouse IWMGQSG dec 2003

  3. TAKE-HOME MESSAGE ORIGINAL DESIGN: Observation during 6 years of scrapie incubation period in 2 half sib families RESULTS: Detection of 2 QTL regions  PrP Toulouse IWMGQSG dec 2003

  4. PLAN EXPERIMENTAL DESIGN QTL DETECTION RESULTS CONCLUSION AND PERSPECTIVES Toulouse IWMGQSG dec 2003

  5. Experimental population=2 half sibs families • to detect the effect of other genes than PrP gene. We used animals which have a susceptible PrP genotype ARQ/VRQ sire1 VRQ/VRQ sire 2 VRQ/VRQ Birth in 1998 Birth in 1999 79 lambs ARQ/VRQ 71 lambs ARQ/VRQ Family 1 Family 2 Toulouse IWMGQSG dec 2003

  6. Genotyping of markers • First objective was to use results of published mouse studies to choose marker in sheep by comparive mapping. • There are now 5 mouse studies which allowed to detect a total of 14 chromosomal regions affecting scrapie incubation period BUT • Comparative mapping between mice and sheep = genome scan 121 molecular markers were typed Toulouse IWMGQSG dec 2003

  7. Scrapie resistance trait = Incubation period Histology Himmunohistochimistry Experimental Design? Assumption : scrapie infection occurs mostly during the lambing period. autopsy birth Clinical signs Infection Scrapie diagnosis If scrapie diagnosis is negative or unknown What happens? Toulouse IWMGQSG dec 2003

  8. Alive at the end of the experiment (n=7) Censored observations (20%) Uncensored observations (80%) MISSING DATA INCUBATION TIME How many animals are measured for incubation period? Clinical signs No Clinical signs Alive at the end of the experiment (n=7) Died at the farm (n=19) Scrapie (n=119) Other (n=5) Toulouse IWMGQSG dec 2003

  9. Distribution of incubation period Animals were observed during 6 years Incubation time(months) Hight Differences for distribution and mean of incubation period  Analyse independently each family Toulouse IWMGQSG dec 2003

  10. PLAN EXPERIMENTAL DESIGN QTL DETECTION RESULTS CONCLUSION AND PERSPECTIVES Toulouse IWMGQSG dec 2003

  11. What Kind of Methods were Used? INCUBATION TIME QTL detection  Interval mapping analysis: maximum likelihood method (QTLMAP software)  to estimate effect and position of the QTL Both families Family 1 Family 2 CH 3 CH 3 CH 3 & 18 Toulouse IWMGQSG dec 2003

  12. A QTL, detected on chromosome 3, affects incubation time in both families Likelihood profile of incubation period 5% chromosomal level Toulouse IWMGQSG dec 2003

  13. A QTL, detected on chromosome 18, affects incubation time in family 2 Likelihood profile of incubation period 1% chromosomal level 5% chromosomal level This region corresponds to mouse chromosomes 2 & 12 Toulouse IWMGQSG dec 2003

  14. PLAN EXPERIMENTAL DESIGN QTL DETECTION RESULTS CONCLUSION AND PERSPECTIVES Toulouse IWMGQSG dec 2003

  15. Conclusion • In sheep like in mice: other genes than PrP seem to have an effect on scrapie resistance. • In sheep, QTL controlling incubation period were detected on chromosome 3 and 18. • Marker densification began on chromosome 18. 16 markers were typed Toulouse IWMGQSG dec 2003

  16. In the FUTURE … • Confirmation of QTL with an interval mapping method using a survival Cox model Taking into account censored data • Maker densification to identify new resistant genes in the QTL regions • Confirmation of QTL in other populations with or without the same PrP genotype Toulouse IWMGQSG dec 2003

  17. Acknowledgements Toulouse IWMGQSG dec 2003

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