Short telomeres drive pessimistic judgment bias in zebrafish

The role of telomerase reverse transcriptase (TERT) has been widely investigated in the contexts of aging and age-related diseases. Interestingly, decreased telomerase activities (and accelerated telomere shortening) have also been reported in patients with emotion-related disorders, opening the possibility for subjective appraisal of stressful stimuli playing a key role in stress-driven telomere shortening. In fact, patients showing a pessimistic judgment bias have shorter telomeres. However, these evidences in humans are correlational and the causal inference of pessimism driving shortening of telomeres has not been established experimentally yet. We have developed and validated a judgment bias experimental paradigm to measure subjective evaluations of ambiguous stimuli in zebrafish. This behavioral assay allows classifying individuals in an optimistic-pessimistic dimension (i.e. from individuals that consistently evaluate ambiguous stimuli as negative to others that perceived them as positive). Using this behavioral paradigm we found that telomerase-deficient zebrafish (tert^−/−) were more pessimistic in response to ambiguous stimuli than WT zebrafish. The fact that individuals with constitutive shorter telomeres have pessimistic behaviors demonstrate for the first time in a vertebrate model a genetic basis of judgment bias.