Telomere repeat-binding factor 2 (TRF2) is critical for telomere integrity in dividing stem and somatic cells, and its role is essential for vertebrate early development because animals carrying a null terf2 mutation have early embryonic lethality due to an unknown molecular mechanism. Besides telomeric homeostasis by protecting telomere ends, it has been shown that TRF2 can interact with the neuronal gene-silencer repressor element 1-silencing transcription factor (REST), whose instability via TRF2 affects neuronal cell differentiation in vitro. However, the mechanism that couples TRF2-mediated features to cellular differentiation programs has yet to be elucidated in vivo. Loss of TRF2 in zebrafish embryos recapitulates key aspects of telomere attrition, including the DNA-damage response and cell-cycle arrest, as well as neurodegeneration. Intriguingly, TRF2-deficient animals develop similar but more severe neuromuscular defects observed in spinal muscular atrophy, a genetic disorder characterized by a loss of alpha motoneurons in the spinal cord. Using terf2 zebrafish embryos that carry the concurrent triple- or quadruple-defects of the rest, tert, tp53 and/or terf1 genes with the expression of the various transgenic reporter genes including the zebrabow system, we show motor axon-specific pathfinding/guidance abnormalities that could be linked to aberrant Wnt and Hedgehog pathways in parallel with telomere fusion/attrition. Our results show for the first time, in vivo, that TRF2 functions in motor axon development and suggest that terf2 mutation leads to early developmental senescence and motoneuron defects in both telomere-dependent and -independent manners.