Comparison of sperm quality and DNA integrity in mouse sperm exposed to various cooling velocities and osmotic stress |
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Authors: | Cengiz Yildiz Napoleon Law Keith Jarvi |
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Institution: | a Physiology and Experimental Medicine Research Program, The Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8 b Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada M5G 1X8 c Department of Reproduction and Artificial Insemination, Faculty of Veterinary Medicine, University of Mustafa Kemal, Hatay, Turkey d Division of Urology, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada M5G 1X6 |
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Abstract: | The first objective was to compare sperm quality following conventional manual sperm freezing (cryovials held 1, 2, 3, and 4 cm, respectively, above liquid nitrogen (LN2) for 10 min, resulting in cooling velocities of approximately −14.9, −10.1, −6.6, and −5.1 °C/min, respectively), and cooling velocities of −5, −20, −40, and −100 °C/min in a programmed automated freezer, for sperm recovered from CD-1, B6129SF1, and C57BL/6NCrlBR mice. Furthermore, using these strains, as well as 129S/SvPaslco, and DBA/2NCrlBR mice, the second objective was to determine the effects on DNA integrity of sperm exposed to hyposmotic (1 mOsm/L) and hyperosmotic (2400 mOsm/L) solutions, compared to an isosmotic control (300 mOsm/L). For freezing above LN2 or in an automated freezer, 2 cm above LN2 and −100 °C/min, respectively, were optimal (P < 0.05-0.01), with no significant differences between these two approaches for post-thaw progressive motility, DNA integrity, and in vitro rates of fertilization and blastocyst formation. Both manual and automated freezing techniques increased post-thaw sperm DNA fragmentation (P < 0.01); the DNA integrity of post-thaw sperm was significantly affected by cooling velocity and strain background. Relative to isosmotic controls, a hyposmotic solution was more deleterious (P < 0.05-0.01) to sperm DNA integrity than a hyperosmotic solution for CD-1, B6129SF1, C57BL/6, and DBA mice (there were strain-dependent differences). In conclusion, optimization of freezing distance and cooling velocity (manual and automated freezing, respectively) were significant factors for efficient cryopreservation and re-derivation of mice from frozen-thawed sperm. Additionally, osmotically-driven volume changes in mouse sperm increased DNA fragmentation, with susceptibility affected by background strain. |
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Keywords: | Sperm Embryo Cryopreservation DNA integrity In vitro fertilization Mouse |
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