Abstract
Clinical applications of oocytes cryopreservation include preservation of future fertility of young cancer patients, substitution of embryo freezing to avoid associated legal and ethical issues, and delaying childbearing years. While the outcome of oocyte cryopreservation has recently been improved, currently used vitrification method still suffer from increased biosafety risk and handling issues while slow freezing techniques yield overall low success. Understanding better the mechanism of cryopreservation-induced injuries may lead to development of more reliable and safe methods for oocyte cryopreservation. Using the mouse model, a microarray study was conducted on oocyte cryopreservation to identify cryoinjuries to transcriptionally active genome. To this end, metaphase II (MII) oocytes were subjected to standard slow freezing, and then analyzed at the four-cell stage after embryonic genome activation. Non-frozen four-cell embryos served as controls. Differentially expressed genes were identified and validated using RT-PCR. Embryos produced from the cryopreserved oocytes displayed 200 upregulated and 105 downregulated genes, associated with the regulation of mitochondrial function, protein ubiquitination and maintenance, cellular response to stress and oxidative states, fatty acid and lipid regulation/metabolism, and cell cycle maintenance. These findings reveal previously unrecognized effects of standard slow oocyte freezing on embryonic gene expression, which can be used to guide improvement of oocyte cryopreservation methods.
Highlights
Successful oocyte cryopreservation is of interest to preserve future fertility of cancer patients undergoing chemo- and radiotherapy, to substitute embryo freezing toward avoiding associated legal and ethical issues, to prolong childbearing years, and to conserve endangered species
To study lasting cryoinjuries to active transcriptome, a total of 1,170 metaphase II (MII) oocytes were cryopreserved by widely used standard slow freezing
Of 753 frozen-thawed and intact oocytes, 493 were fertilized as assessed by cleavage to the two-cell stage and 310 of the two-cell embryos developed to the four-cell stage
Summary
Successful oocyte cryopreservation is of interest to preserve future fertility of cancer patients undergoing chemo- and radiotherapy, to substitute embryo freezing toward avoiding associated legal and ethical issues, to prolong childbearing years, and to conserve endangered species. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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