Modulation of Pleurodeles waltl DNA Polymerase mu Expression by Extreme Conditions Encountered during Spaceflight

DNA polymerase m is involved in DNA repair, V(D)J recombination and likely somatic hypermutation of immunoglobulin genes. Our previous studies demonstrated that spaceflight conditions affect immunoglobulin gene expression and somatic hypermutation frequency. Consequently, we questioned whether Polm expression could also be affected. To address this question, we characterized Polm of the Iberian ribbed newt Pleurodeles waltl and exposed embryos of that species to spaceflight conditions or to environmental modifications corresponding to those encountered in the International Space Station. We noted a robust expression of Polm mRNA during early ontogenesis and in the testis, suggesting that Polm is involved in genomic stability. Full-length Polm transcripts are 8–9 times more abundant in P. waltl than in humans and mice, thereby providing an explanation for the somatic hypermutation predilection of G and C bases in amphibians. Polm transcription decreases after 10 days of development in space and radiation seem primarily involved in this downregulation. However, space radiation, alone or in combination with a perturbation of the circadian rhythm, did not affect Polm protein levels and did not induce protein oxidation, showing the limited impact of radiation encountered during a 10-day stay in the International Space Station.