1. Figure 1: Breeding programme for generation of congenic mice
1.International Livestock Research Institute
2Wellcome Trust Project
Congenic mice models for the discovery of trypanotolerant genes in cattle
J.Wambugu1,2
M.Ogugo1,2
N.Nyamweya1,2
S.Kemp1,2
M.Agaba1,2
Introduction
Research at ILRI has revealed three regions ( QTL) on mouse chromosomes 1, 5, and 17 termed Tir3, 2, and 1 respectively, that are responsible for resistance to T.congolense infection in the laboratory mouse strain C57BL6. A breeding programme where the resistant C57BL were crossed ,backcrossed and intercrossed with the trypano-susceptible AJ mouse strain was undertaken. The aim of the programme was to develop three lines of congenic mice where each line carried only one of the three Tir resistant C57BL6 locus against a susceptible AJ strain genetic background. Subsequently the three lines were infected with T.congolense parasites.
Key findings
It was confirmed that the QTLs work independently of each other . The QTL Tir3 was lost in this work and mice of this line had same survival time with that of the control.
Further studies using the congenic mice approach will further clarify candidate genes in trypanotolerance in livestock.
Congenic mouse strains are valuable tools in the genetic analysis of disease resistance traits in livestock.
Method
C57BL/6 male mice were crossed with A/J females to produce an F1 population.. Specific polymorphic micro satellite markers ( Figure 1 ) were used to genotype this F1 population for selection at the three loci..
Only male mice that were heterozygous ( AC) at each respective locus were selected and backcrossed to A/J females. This was repeated up to the 9th generation while genotyping and selecting for the C57 haplotype at each generation interval.
The 9th generation congenic mice populations ( Tir1AC, Tir2AC and Tir3AC) were intercrossed to produce ( Tir1CC, Tir2CC, and Tir3CC) and Tir1AA, Tir1AA,Tir3AA).This population was infected with 104 T.Congolense parasites intraperitoneally.
Tir1AA, Tir2AA & Tir3AA mice strains acted as A/J controls. Survival data was collected over a period of 100 days.
AJ X C57BL6
F1 GENOTYPE
GENOTYPE
F1 ♂ X AJ ♀
AC AA AC
BC 1
AC ♂ X AJ ♀
AC AA AC
BC 2
Repeat until backcross 9 then intercross the BC9 and GENOTYPE
AC AA CC
CC X CC
AA X AA
CC CC CC
AA AA AA
Figure 1: Breeding programme for generation of congenic mice
These are the congenic strains
Results
Congenic strains of mice with respective single C57B/6 QTL loci against a background of A/J mice strain were successfully established for use in recombination experiments and microarray expression analysis for gene discovery.
Following infection with T.congolense parasites different survival times were evident for the three congenic mice strains that differed at only one QTL (Figure 2)
Expression analysis from challenged mice differing only at one QTL will allow dissection of the effects of each QTL.
Exceptional conservation of synteny can reflect important functional relationships between genes.
ILRI
I NTERNATIONAL LIVESTOCK RESEARCH INSTITUTE