Functional activity of mitochondria in native and devitrified Bos Taurus oocytes during in vitro maturation

Difficulties in developing an effective technology for vitrification of female gametes are connection with the features of the structure of oocytes, the sensitivity of cellular compartments to the action of ultralow temperatures, the toxicity of cryoprotectants. The aim of this study is to evaluate the effect of pre-treatment (before vitrification) of Bos Taurus oocytes with fluid of follicles (FF) d ≤3 mm on mitochondrial activity (MA) in thawed oocytes. MA was evaluated in: native oocytes; native oocytes treated with FF; devitrified oocytes; devitrified oocytes treated with FF (120 min, 37 ° C). The oocyte-cumulus complexes were vitrified in accordance with the method described by us earlier (Kuzmina T. Et al., Gen. & Breed. of Anim., 2014, № 4, p. 15-19). The devitrified oocytes were cultured in TC-199 medium with 20% fetal bovine serum, 50 ng / ml bovine prolactin (Sigma) together with 1x10⁶cells / ml of granulosa for 24 hours at 38.5 ° C in 5% CO₂ and 90% of humidity. Mitochondria were visualized with Mito Tracker Orange CMTMRos (MTOCMTMRos, Sigma). Indicators of MA were expressed in the levels fluorescence intensity of MTOCMTMRos (IFMTOCMTMRos, μA) and were estimated in the stages of diplotene, metaphase -I and II. Before cultivation the level of MA was significantly higher in native oocytes than in devitrified oocytes (337 ± 17.4 μA and 319 ± 16.8 μA vs. 87 ± 9.2 μA and 171 ± 14.5 μA, P <0.01). The level of MA have increased in metaphase I and II stages in devitrified oocytes at pre-treated oocytes with FF (131 ± 10.9 μA vs. 201 ± 8.7 μA and 109 ± 9.9 μA vs. 151 ± 12.8 μA, P <0.01). There were no differences in the level of MA in metaphase I and II stages native oocytes and oocytes that have pre-treatment by FF. The obtained results supplement data concerning to the functioning of cellular compartments (mitochondria) in female animals gametes at the influence of ultralow temperatures.

Bos Taurus, oocyte, in vitro maturation, mitochondria, vitrification, Bos Taurus

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