Cryopreservation of mouse oocytes: mutagenic effects in the embryo?

We have shown in previous studies that the complete cycle of cryopreservation and prefreezing manipulations increases the degeneration and decreases the fecundability of mouse oocytes. The present study confirms these results. Moreover, we show that the increase of polyploidy previously observed in one-cell zygotes derived from frozen-thawed oocytes persists during the early stages of embryonic development. Furthermore, embryos obtained from frozen oocytes or oocytes exposed to prefreezing manipulations show an increase in the frequency of sister chromatid exchanges. Since the estimation of sister chromatid exchange is a sensitive test of mutagenicity, this suggests that the complete cycle of cryopreservation might alter the oocyte and, more particularly, induce DNA damage.