Segmentally trisomic Ts65Dn mice provide a postnatal model for Down syndrome. Cesium irradiation was used to produce a reciprocal translocation, T (16;17) 65Dn. One of the translocation chromosomes is a small marker chromosome, comprised of the centromere and proximal end of Chr 17 (~9.5Mb) and the distal end of mouse Chr 16 (~34Mb). Translocation heterozygous (T/+) females produced progeny trisomic for this small translocation product and a stock was established in which Ts65Dn mice are trisomic for the genes carried in the small translocation chromosome, symbolized Ts(1716)65Dn.
The precise locations of the Chr 16 and Chr 17 breakpoints are 84,351,351 bp and 9,426,822 bp, respectively. The Chr 16 segment contains about two thirds of the human Chr 21 homologues in the mouse, from mitochondrial ribosomal protein L39 (Mrpl39) gene to the distal telomere. These data were used to generate a PCR genotyping assay for Ts65Dn (Reinholdt et al., 2011), replacing the previous methods of chromosome analysis or qPCR. Northern and Western blotting, enzyme activity assays and reverse phase protein arrays (RPPA) demonstrate that some but not all genes in the translocation product are expressed at elevated levels in segmentally trisomic animals. RPPA shows a loss of correlation among some brain proteins (Ahmed et al., 2012).
Stock No. 001924 is the original trisomic Ts(1716)65Dn strain. However, Pde6brd1, the recessive retinal degeneration 1 mutation, is segregating in this stock; Pde6brd1 homozygotes are blind. Stock No. 005252 is an alternative strain, with a virtually identical genetic background except that it is wild-type for Pde6b, the result of continuous backcrossing to (C57BL/6JEiJ x C3Sn.BLiA-Pde6b+/DnJ)F1/J.
The Ts65Dn strains (001924 and 005252) are maintained by crossing Ts65Dn trisomic females to B6EiC3SnF1/J (001875) or (C57BL/6JEiJ x C3Sn.BLiA-Pde6b+/DnJ)F1/J (003647) males, respectively. Ts65Dn females generally breed well with an average litter size of 5-8 and the mothers take good care of their pups. The environment seems to have a profound effect on these mice. They are on a fourteen hour light and 10 hour dark cycle, mated as single pairs, with mates kept together throughout their six month breeding rotation, and noise is kept to a minimum. It is preferable to have them maintained and handled by one person. The diet is especially important, as malnourished mothers will not nurse their pups. Most facilities provide maintenance and breeding chows and Ts65Dn should be on the latter. Ts65Dn mice at The Jackson Laboratory are fed the LabDiet® 5K52/5K67 diet with a 6% fat content.
The incidence of trisomy varies among litters (ranging from 20-50%) with some females transmitting the trisomy more readily than others. Ts65Dn males are functionally sterile although the numbers of sperm vary from male to male. The recessive retinal degeneration 1 mutation (Pde6brd1) is segregating in the 001924 colony which results in blindness in homozygotes, whereas the 005252 colony is homozygous wild-type for Pde6b.
All progeny are genotyped by PCR or qPCR, see Protocols for details.