Identification and characterization of a new Down syndrome model, Ts[Rb(12.1716)]2Cje, resulting from a spontaneous Robertsonian fusion between T(1716)65Dn and mouseChromosome 12

The segmental trisomy model, Ts65Dn, has been a valuable resource for the study of the molecular and developmental processes associated with the pathogenesis of Down syndrome. However, male infertility and poor transmission of the small marker chromosome, T(17¹⁶)65Dn, carrying the distal end of mouse Chromosome 16 (MMU16) are limiting factors in the efficient production of these animals for experimental purposes. We describe here the identification and preliminary characterization of mice, designated Ts[Rb(12.17¹⁶)]2Cje, carrying a chromosomal rearrangement of the Ts65Dn genome whereby the marker chromosome has been translocated to Chromosome 12 (MMU12) forming a Robertsonian chromosome. This stable rearrangement confers fertility in males and increases the frequency of transmitted segmental trisomy through the female germline. We confirm retention of a dosage imbalance of human Chromosome 21 (HSA21)-homologous genes from App to the telomere and expression levels similar to Ts65Dn within the triplicated region. In addition, we characterized the dendritic morphology of granule cells in the fascia dentata in Ts[Rb(12.17¹⁶)]2Cje and 2N control mice. Quantitative confocal microscopy revealed decreased spine density on the dendrites of dentate granule cells and significantly enlarged dendritic spines affecting the entire population in Ts[Rb(12.17¹⁶)]2Cje as compared to 2N controls. These findings document that the structural dendritic spine abnormalities are similar to those previously observed in Ts65Dn mice. We conclude that this new model of Down syndrome offers reproductive advantages without sacrificing the integrity of the Ts65Dn model.