Ultrastructure of bovine blastocysts following cryopreservation: Effect ofmethod of blastocyst production

The objective of this study was to describe the ultrastructure of blastocys ts derived by in vivo and in vitro methods and to investigate how the morph ology is affected by exposure to cryoprotectant (10% glycerol) or cryoprese rvation by conventional slow freezing. In vivo derived blastocysts were cha racterized by a narrow perivitelline space (PvS), a continuous cover of num erous slacked microvilli (MV) on the plasma membrane, a well-defined system of cell-to-cell coupling and a large population of round or elongated mito chondria with numerous transverse cristae. Exposure of these blastocysts to cryoprotectant was manifested by shrinkage of the blastocysts and swelling of the mitochondria. Cryopreservation resulted in further shrinkage, damag e to the MV, and accumulation of cellular debris, in comparison, the in vit ro matured (lVM)/in vitro fertilized (IVF) in vivo cultured blastocysts dis played a wider PvS; they appeared to possess less MV and all blastocysts di splayed some cellular debris in their PvS. There was also a decrease in the number of junctional contacts between the trophoblastic cells. The reactio n of these blastocysts to exposure to cryoprotectant was similar to that of the in vivo derived blastocysts. However, they appeared to be more suscept ible to cryopreservation. The totally in vitro produced (IVP) blastocysts d isplayed a wider PvS, no stacking of the MV, increased numbers of lipid dro plets and a further reduction in the junctional contacts between trophoblas tic cells. The IVP blastocysts sustained breakage of the zona pellucida on exposure to cryoprotectant and were extremely sensitive to cryopreservation , losing ail cell structure and organization. The findings of the present s tudy indicate that in vivo derived blastocysts possess certain structural c haracteristics that confer a greater tolerance on them to exposure to cryop rotectant and cryopreservation. (C) 2001 Wiley-Liss, Inc.