“Normal” Mice Have Normal Telomeres

In a recent article, Smoom et al. identified an important amino acid variation in the helicase RTEL1 of the Algerian mouse (Mus spretus). Since the latter has telomeres five times shorter than the laboratory mouse (belonging to the Mus musculus species), they introduced this variation in laboratory mice, in order to obtain an engineered strain with human-length telomeres. Succeeding in doing this, they established the “Telomouse” strain. Here I demonstrate that, in reality, Mus spretus does not show this variation: the key amino acid is conserved in all rodent species, which all have human-length telomeres (including wild Mus musculus species). This finding in no way compromises the value of the research of Smoom et al. and the utility of the Telomouse strain. Rather, it raises the question of how the telomere length of Mus musculus (as a species) should be considered and the important consequences it has on studies on inter-species comparison.