Abstract
The objective of this study was to evaluate the effects of different maturation systems on oocyte resistance after vitrification and on the phospholipid profile of the oocyte plasma membrane (PM). Four different maturation systems were tested: 1) in vitro maturation using immature oocytes aspirated from slaughterhouse ovaries (CONT; n = 136); 2) in vitro maturation using immature oocytes obtained by ovum pick-up (OPU) from unstimulated heifers (IMA; n = 433); 3) in vitro maturation using immature oocytes obtained by OPU from stimulated heifers (FSH; n = 444); and 4) in vivo maturation using oocytes obtained from heifers stimulated 24 hours prior by an injection of GnRH (MII; n = 658). A sample of matured oocytes from each fresh group was analyzed by matrix associated laser desorption-ionization (MALDI-TOF) to determine their PM composition. Then, half of the matured oocytes from each group were vitrified/warmed (CONT VIT, IMA VIT, FSH VIT and MII VIT), while the other half were used as fresh controls. Afterwards, the eight groups underwent IVF and IVC, and blastocyst development was assessed at D2, D7 and D8. A chi-square test was used to compare embryo development between the groups. Corresponding phospholipid ion intensity was expressed in arbitrary units, and following principal components analyses (PCA) the data were distributed on a 3D graph. Oocytes obtained from superstimulated animals showed a greater rate of developmental (P<0.05) at D7 (MII = 62.4±17.5% and FSH = 58.8±16.1%) compared to those obtained from unstimulated animals (CONT = 37.9±8.5% and IMA = 50.6±14.4%). However, the maturation system did not affect the resistance of oocytes to vitrification because the blastocyst rate at D7 was similar (P>0.05) for all groups (CONT VIT = 2.8±3.5%, IMA VIT = 2.9±4.0%, FSH VIT = 4.3±7.2% and MII VIT = 3.6±7.2%). MALDI-TOF revealed that oocytes from all maturation groups had similar phospholipid contents, except for 760.6 ([PC (34:1) + H]+), which was more highly expressed in MII compared to FSH (P<0.05). The results suggest that although maturation systems improve embryonic development, they do not change the PM composition nor the resistance of bovine oocytes to vitrification.
Highlights
The ability to preserve female gametes is an integral part of assisted reproductive techniques (ARTs) and can have a significant impact on animal conservation programs, animal breeding programs, and human-assisted conception [1, 2].For animal production, oocyte cryopreservation is crucial for overcoming the logistical problems associated with the numbers of recovered oocytes, their transportation to the lab and the availability of recipients for the produced embryos
The main objective of this study was to compare the resistance of oocytes that had been maturated using different systems to vitrification and warming by evaluating blastocyst development and quality after in vitro fertilization (IVF) and culture (IVC)
A greater percentage (P
Summary
Oocyte cryopreservation is crucial for overcoming the logistical problems associated with the numbers of recovered oocytes, their transportation to the lab and the availability of recipients for the produced embryos These issues are of particular concern in large-scale commercial embryo production programs. Oocyte cryopreservation remains an ineffective technique for most domestic animals, due to the very low ability of cryopreserved oocytes from most species to undergo proper embryonic development This high sensitivity of oocytes to cryopreservation could be explained by their unique morphological characteristics such as cell size, cytoplasmic water volume and cytoskeletal organization [3,4,5,6,7,8,9,10]. Cryopreserved oocytes may suffer severe morphological and functional damage that can be exacerbated due to the high cytoplasmic lipid content and to the phospholipid composition of the membrane [11]
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